Ecosystem, or ecological system (from other Greekοἶκος - dwelling, residence and σύστημα - system) - a biological system consisting of a community of living organisms ( biocenosis), their habitats ( biotope), a system of connections that exchanges matter and energy between them. One of the basic concepts ecology.Ecosystem example - pond with those who live in it plants, fish, invertebrates, microorganisms, constituting the living component of the system, biocenosis. A pond as an ecosystem is characterized by bottom sediments of a certain composition, chemical composition ( ionic composition, concentration dissolved gases) and physical parameters ( water transparency, trend annual changes temperature), as well as certain indicators biological productivity, trophic status reservoir and specific conditions of this reservoir. Another example of an ecological system is deciduous Forest in central Russia with a certain composition of forest litter, characteristic of this type of forest soil and sustainable plant community, and, as a result, with strictly defined indicators microclimate(temperature, humidity, illumination) and corresponding to such environmental conditions complex of animal organisms. An important aspect that makes it possible to determine the types and boundaries of ecosystems is the trophic structure of the community and the ratio biomass producers, its consumers And biomass-destroying organisms, as well as indicators of productivity and metabolism and energy.
Ecosystem classification:
microecosystems(a lichen pillow, a drop of water from a lake, a drop of blood with cells, etc., Fig. 53);
mesoecosystems(pond, lake, steppe, etc.);
macroecosystems(continent, ocean);
global ecosystem(biosphere of the Earth), or ecosphere, integration of all ecosystems of the world.
39. Composition and structure of ecosystems. The spatial structure of the ecosystem.
The structure of ecosystems. Ecosystems consist of living and non-living components, called respectively biotic and abiotic. The totality of living organisms of the biotic component is called a community. The study of ecosystems includes, in particular, the elucidation and description of the close relationships that exist between the community and the abiotic component. It is useful to divide the biotic component into autotrophic and heterotrophic organisms. Thus, all living organisms will fall into one of two groups. Autotrophs synthesize the organic substances they need from simple inorganic substances and, with the exception of chemotrophic bacteria, do it through photosynthesis, using light as an energy source. Heterotrophs need a source of organic matter and (with the exception of some bacteria) use the chemical energy contained in the food they eat. Heterotrophs depend on autotrophs for their existence, and understanding this dependence is essential to understanding ecosystems. The non-living, or abiotic, component of an ecosystem mainly includes 1) soil or water and 2) climate. Soil and water contain a mixture of inorganic and organic substances. Soil properties depend on the parent rock on which it lies and from which it is partially formed. The concept of climate includes such parameters as illumination, temperature and humidity, which to a large extent determines the species composition of organisms successfully developing in a given ecosystem. For aquatic ecosystems, the degree of salinity is also very significant.
The composition of the ecosystem. The ecosystem includes living organisms (their totality is called biogeocenosis or biota of the ecosystem), and non-living (abiotic) factors - the atmosphere, water, nutrients, light and dead organic matter - detritus.
The spatial structure of most ecosystems is determined by the tiered arrangement of vegetation
ChapterII. Ecological systems
Topic 2. Concepts about ecosystems
2.1. General characteristics of the ecosystem
The term "ecosystem" was proposed by the English scientist - botanist - ecologist A. Tensley in 1935, although the idea of the relationship and unity of organisms and their habitat was expressed by ancient scientists. Only at the end of the last century, publications began to appear that included concepts identical to the term “ecosystem”, which came simultaneously in American, Western European and Russian scientific literature. So, the German scientist K. Mobius in 1877. introduced the term “biocenosis”, 10 years later the American biologist S. Ferbe published his classic work on the lake as an aquatic ecosystem. in his writings, he noted the unity of living organisms with the parent rock of soil transformation. Nature functions as an integral system, regardless of what kind of environment we are talking about - freshwater, marine, terrestrial and underground. But only in the middle of the 20th century was the general theory of systems developed, and the development of a new, quantitative direction in ecosystem ecology began. The founders of this direction were F. Khabchinson, R. Margalef, K. Watt, P. Petten, G. Odum.
Ecosystem - includes all organisms (biotic community) cooperatively functioning in a particular area, which interact with the physical environment in such a way that the flow of energy creates well-defined biotic structures and the circulation of substances between living and non-living parts.
2.2. Ecosystem Composition
The ecosystem includes living organisms (their totality can be called a biocenosis or ecosystem biota), non-living (abiotic) factors - the atmosphere, water, nutrients, light and dead organic matter - detritus.
All living organisms are divided into two groups according to the method of nutrition - autotrophs(from Greek words autos- myself and tropho- food) and heterotrophs(from the Greek word heteros - another).
Autotrophs use inorganic carbon and synthesize limited substances from inorganic, this is producers ecosystems. According to the source of energy, they, in turn, are also divided into two groups.
Photoautotrophs- solar energy is used for the synthesis of organic substances. These are green plants that have chlorophyll (and other pigments) and absorb sunlight. The process by which it is absorbed is called photosynthesis.
Chemoautotrophs- chemical energy is used for the synthesis of organic substances. These are sulfur bacteria and iron bacteria that obtain energy from the oxidation of sulfur and iron compounds. Chemoautotrophs play a significant role only in groundwater ecosystems. Their role in terrestrial ecosystems is relatively small.
Phytophages(herbivores). These include animals that feed on living plants. Among phytophages there are also small animals, such as aphids or grasshoppers, and giants, such as elephants. Phytophages are almost all agricultural animals: cows, horses, sheep, rabbits. There are phytophages among aquatic organisms, for example, grass carp, eating plants that overgrow irrigation canals. An important phytophage is the beaver. It feeds on tree branches, and from the trunks it builds dams that regulate the water regime of the territory.
Zoophages (predators, carnivores). Zoophages are varied. These are small animals that feed on amoebas, worms or crustaceans. And big ones, like a wolf. Predators that feed on smaller predators are called second-order predators. There are plants - predators (dew, pemphigus), which use insects as food.
Symbiotrophs.These are bacteria and fungi that feed on the root secretions of plants. Symbiotrophs are very important for the life of the ecosystem. Threads of fungi that entangle the roots of plants help the absorption of water and minerals. Bacteria, symbiotrophs absorb gaseous nitrogen from the atmosphere and bind it into compounds available to plants (ammonia, nitrates). This nitrogen is called biological (in contrast to the nitrogen of mineral fertilizers).
Symbiotrophs also include microorganisms (bacteria, unicellular animals) that live in the digestive tract of animals - phytophages and help them digest food. Animals such as cows, without the help of symbiotrophs, are not able to digest the grass they eat.
Detritivores organisms that feed on dead organic matter. These are centipedes, earthworms, dung beetles, crayfish, crabs, jackals and many others.
Some organisms eat both plants and animals and even detritus and are euryphages (omnivores) - bear, fox, pig, rat, chicken, crow, cockroach. Euryphage is also a man.
Reducers - organisms that, by their position in the ecosystem, are close to detritivores, since they also feed on dead organic matter. However, decomposers - bacteria and fungi - break down organic matter to mineral compounds, which return to the soil solution and are again used by plants.
Organic substances created by autotrophs serve as food and a source of energy for heterotrophs: consumers - phytophages eat plants, first-order predators - phytophages, second-order predators - second-order predators, etc. This sequence of organisms is called food chain, its links are located at different trophic levels (represent different trophic groups).
Reducers need time to process corpses. Therefore, in an ecosystem there is always detritus- stock of dead organic matter. Detritus is leaf litter on the surface of forest soil (remains 2-3 years), the trunk of a fallen tree (remains 5-10 years), soil humus (remains hundreds of years), deposits of organic matter on the bottom of the lake - sapropel - and peat in the swamp ( preserved for thousands of years). The longest lasting detritus are coal and oil.
Table 2.1.
Representatives of different trophic groups of some ecosystems.
Trophic Forest Pond Agricultural
land group
Producers Spruce, birch, pondweed, water lily, wheat, rye, potatoes,
Consumers - Elk, hare, Muskrat, thick - Man, cow, sheep, mouse,
phytophages lobik squirrel, daphnia vole, weevil, aphids
Consumers - Wolf, fox Seagull, perch, ide, Man, starling, divine
zoophagous ferret pike, catfish cow
Consumers - Beetle - dead - Perlovitsa, Larvae of beetles and flies,
detritophages voed, kivsyak, bloodworm, earthworm
rain daphnia
Table 2.1. examples of representatives of different trophic groups for some ecosystems are given.
2.3. Conditions for the functioning of the ecosystem
An ecosystem is a complex system. Complex systems have a number of properties, such as emergence, the principle of the necessary diversity of elements, stability, the principle of non-equilibrium, the type of metabolism or energy, and evolution.
Emergence (from the English emergence - unexpectedly emerging) of a system is the degree of irreducibility of the properties of the system to the properties of its constituent elements. The properties of the system depend not only on its constituent elements, but also on the characteristics of the interaction between them (for example, the phenomenon of synergy, when the interaction of some toxic compounds results in even more toxic substances).
The principle of the necessary diversity of elements comes down to the fact that any system cannot consist of exactly the same elements, moreover, the variety of elements that make up it is necessary condition functioning. The lower limit of diversity is equal to two, the upper one tends to infinity. The diversity and presence of different phase states of the substances that make up an ecosystem determine its heterogeneity.
Stability of a dynamic system and its ability to self-preservation depends on the predominance of internal interactions over external ones. If an external impact on a biological system exceeds the energy of its internal interactions, then this can cause irreversible changes or the death of the system. A stable or stationary state of a dynamic system is maintained by continuously performed external work, which requires the influx of energy, its transformation in the system and outflow from the system.
Non-equilibrium principle It boils down to the fact that systems functioning with the participation of living organisms are open, therefore, they are characterized by the inflow and outflow of energy and matter, which cannot be carried out in an equilibrium state. Consequently, any ecosystem is an open, dynamic, non-equilibrium system.
Table 2.2
Behavior of Systems in Equilibrium and Non-Equilibrium Regions
Non-equilibrium state Equilibrium state
The system “adapts” to external
conditions, changing its structure to another, strong perturbations are required
or changes in boundary conditions
Multiple Stationary One Stationary State
states
Sensitivity to fluctuations Insensitivity to fluctuations
(small influences lead to
big consequences, domestic
fluctuations become large)
All parts act in concert Molecules behave independently
Fundamental uncertainty System behavior is determined by linear dependencies
The concept of equilibrium is one of the main provisions in science. From the point of view of such a science as synergetics (from the Greek synergos - acting together; an interdisciplinary field of research on the processes of self-organization and self-disorganization in various systems, including living ones, for example, in populations), there are the following differences between equilibrium and non-equilibrium systems:
1. The system responds to external conditions.
2. The behavior of the system is random and does not depend on the initial conditions, but depends on the prehistory.
3. The influx of energy creates order in the system, therefore, its entropy decreases.
4. The system behaves as a whole.
The system can be in a state of equilibrium and non-equilibrium; however, its behavior differs significantly (Table 2.2).
In accordance with the second law of thermodynamics to an equilibrium state at -
all closed systems go, that is, systems that do not receive energy from outside. In the absence of energy access from the outside, the system tends to a state of equilibrium, in which the entropy is equal to zero. In the case when the system is in a non-equilibrium state, the conditions for the formation of new structures are created, for which the following is necessary: 1) openness of the system; 2) its non-equilibrium state; 3) the presence of fluctuations. The more complex the system, the more numerous are the types of fluctuations that can bring it into an unstable state. However, in complex systems, there are connections between parts that allow the system to maintain a stable state. The ratio between the stability provided by the relationship between the parts and the instability due to the presence of fluctuations determines the stability threshold of the system. If this threshold is exceeded, the system enters a critical state, which is called the bifurcation point. At this point, the system becomes unstable with respect to fluctuations and can move into a new state of stability. This position is of great importance in the evolution of ecosystems. At the bifurcation point, the system, as it were, oscillates between the choice of one of several paths of evolution.
The vast majority of systems in nature are open, exchanging energy, matter and information with the environment. The dominant role in natural processes belongs not to order, stability and balance, but to instability and non-equilibrium, that is, all systems fluctuate. At the bifurcation point, the system cannot withstand and collapses, and at this point in time it is impossible to predict what state it will be in: whether the state of the system will become chaotic or whether it will move to a new, more high level disorder.
The principle of balance in wildlife plays a huge role. A shift in equilibrium between species in one direction can lead to the extinction of both species. For example, the destruction of predators can lead to the destruction of prey, whose pressure on the environment can increase to such an extent that they do not have enough food. In nature, there is a huge number of equilibria that maintain the overall balance in nature.
Equilibrium in living nature is not static, but dynamic and represents a movement around the point of stability. If this point of stability does not change, then such a state is called homeostasis (from the Greek homoios - the same, serene and stasis - immobility, state). Homeostasis is the ability of an organism or system to maintain a stable (dynamic) balance in changing environmental conditions.
According to the principle of equilibrium, any natural system with the flow of energy passing through it tends to develop towards a steady state. Homeostasis, which exists in nature, is carried out automatically due to feedback mechanisms. Young systems with unstable connections, as a rule, are subject to sharp fluctuations and are less able to withstand external perturbations compared to mature systems, the components of which have had time to adapt to each other, that is, they have undergone evolutionary adaptations.
Natural equilibrium means that the ecosystem retains its stable state and some parameters unchanged, despite the influence of environmental factors. Since the ecosystem is an open system, its stable state means that the supply of matter and the flow of energy at the input and output are balanced.
Under the influence of external factors on the ecosystem, it moves from one state of equilibrium to another. This state is called stable equilibrium. According to numerous data, the ecological situation on our planet has not always been the same. Moreover, she experienced drastic changes in all her components. This can be illustrated by the appearance of oxygen in the atmosphere as an example. It is known that the ultraviolet radiation of the Sun, detrimental to living organisms, gave rise to chemical evolution, due to which amino acids arose. Under the influence of ultraviolet radiation, the processes of decomposition of water vapor led to the formation of oxygen and created a layer of ozone, which prevented the penetration of ultraviolet rays to the surface of the Earth. As long as there was no atmospheric oxygen, life could only develop under the protection of a layer of water, which was limited by the depth to which the sun's rays penetrated. Under the influence of selection pressure, photosynthetic organisms appeared that synthesized organic matter and oxygen. The first multicellular organisms appeared after the oxygen content in the atmosphere reached 3% of the current content. The formation of an atmosphere containing oxygen led to a new state of stable equilibrium. Thanks to the ability of green plants of aquatic ecosystems to produce oxygen in quantities exceeding their needs, conditions were created for the emergence of life on land and the rapid colonization of the entire surface of the Earth by organisms. This, in turn, created conditions under which the consumption and production of oxygen equalized and reached the level of 20%. Then fluctuations in the ratio of oxygen to carbon dioxide were observed, and probably at a certain stage of development there was an increase in the content of carbon dioxide in the atmosphere, which served as an impetus for the formation of fossil fuels. Further, the ratio of oxygen and carbon dioxide again came to an oscillatory stationary state. The rapid development of industry, the degradation and transformation of human ecosystems, the burning of fossil fuels and, as a result, the excessive production of carbon dioxide can again make this ratio unstable.
Therefore, balance is an integral element of the functioning of nature, which a person must reckon with as an objective law of nature, the meaning of which he is only beginning to realize.
According to the type of exchange of matter and energy with the environment, systems are classified as follows: 1) isolated systems (exchange is impossible); 2) closed systems (substance exchange is impossible, and energy exchange can occur in any form); 3) open systems (any exchange of matter and energy is possible).
Systems that are interconnected by flows of matter, energy and information are called dynamic. Any living system is a dynamic open system.
Principle of evolution: the emergence, existence and development of all ecosystems is due to evolution. Dynamic self-supporting systems evolve in the direction of complication and the emergence of a system hierarchy (the formation of subsystems). The evolution of any ecosystem leads to an increase in the total flow of energy passing through it. With an increase in the diversity and complexity of the system, evolution accelerates, which is expressed in a faster passage of steps equivalent in qualitative shifts (Akimova, Khaskin, 1998).
Without exception, all ecosystems and even the largest - the biosphere - are open, therefore, for their functioning, they must receive and give energy. For this reason, the concept of an ecosystem must take into account the existence of input and output energy flows that are interconnected and necessary for functioning and self-sustaining, that is, a real functioning ecosystem must have input and, in most cases, outflow paths for processed energy and substances.
The scale of changes in the input and output environment varies greatly and depends on:
The size of the system: the smaller it is, the more it depends on external influences;
Exchange rates: the more intense the exchange, the greater the inflow and outflow;
The balance of autotrophic and heterotrophic processes: the more this balance is disturbed, the greater should be the influx of energy from the outside;
Stages and degrees of system development: young systems differ from mature ones.
The energy of sunlight enters the ecosystem, where photoautotrophic organisms turn it into chemical energy used to synthesize organic compounds from inorganic ones. The flow of energy is directed in one direction: part of the incoming energy of the Sun is transformed by the community and goes to a qualitatively higher level, transforming into organic matter, which is a more concentrated form of energy than sunlight; most of the energy passes through the system and leaves it. In principle, energy can be stored and then released or exported, as shown in the diagram (Figure 2.1), but cannot be reused.
Unlike energy, the batteries and water needed for life can be reused. After the death of living organisms, organic substances decompose and again turn into inorganic compounds. Together, the ecosystem can be represented as a single whole, in which nutrients from the abiotic component are included in the biotic and vice versa, that is, there is a constant circulation of substances with the participation of living (biotic) and non-living (abiotic) components.
E C O S I S T E M A
Sun Energy _____ BIOTIC __ _ Thermal
Light COMPONENT energy
Energy flow
Nutrient cycling
Rice. 2.1 Functional diagram of the ecosystem
For the stable and long-term functioning of an ecosystem, feedbacks are especially important to ensure its autoregulation and self-development. Therefore, regardless of the type of system, its functioning is possible only in the presence of direct (mutual stimulation of the growth and development of organisms) or reverse (for example, inhibition of the development of a population as a result of pressure from a predator) links.
In self-regulating systems, which include ecosystems, an important role belongs to negative reverse connections. All mechanisms of physiological functions in any organism and maintaining the constancy of the internal environment and internal relationships of any self-regulating system are based on the principle of negative feedback.
Consider this provision on the example of self-purification of reservoirs. Let us assume that under the influence of external factors (the influx of fertile soil and nutrients into the reservoir), an increased development of phytoplankton began. This leads to an increase in the growth of zooplankton and a decrease in the concentration of minerals, which contributes to a more rapid grazing of phytoplankton and a decrease in its growth. After some time, there is a decrease in the reproduction of animals due to lack of food. A temporary increase in the biomass of hydrobionts leads to an increase in the mass of detritus, which, being food for bacteria, causes their increased reproduction. Bacteria, in turn, decompose detritus and thereby release nutrients. Thus, the cycle closes and conditions for the enhanced development of phytoplankton reappear in the reservoir. The system as a whole has a negative inverse sign.
Positive Feedback, on the contrary, do not contribute to regulation, but cause destabilization of systems, leading them either to oppression and death, or to acceleration of growth, which, as a rule, is followed by breakdown and destruction. For example, in any plant community, soil fertility, plant yield, the amount of dead plant residues and humus formed form a positive feedback loop. Such a system is in an unstable balance, since the loss of soil and nutrients as a result of erosion or the removal of part of the crop without compensating for the removal of nutrients gives impetus to a decrease in soil fertility and plant productivity. Our ancestors encountered this phenomenon in the era of slash-and-burn agriculture, when, as a result of the withdrawal of products without compensation for removal, soil fertility sharply decreased, which forced people to leave some plots and develop new ones.
In complex ecosystems, there is always a combination of the contours of both signs. If there are loops with a large number of connections, the rule is implemented, which says: with an even number of consecutive negative connections, the loop acquires positive feedback (minus and minus give a plus). However, the development and sustainable functioning of ecosystems is ultimately determined by the presence of feedback loops. To change the behavior of the system, it is important to add or remove links that could change the sign of the system.
Thus, the components of an ecosystem are the flow of energy, the circulation of substances, the biotic and abiotic components, and control feedback loops.
2.4. The role of the structural elements of the ecosystem in its functioning
Features of the flow of energy and biogenic elements in ecosystems are determined by producers, consumers and decomposers.
Producers(from lat. Producentis - producing, creating) are represented by autotrophic organisms, which, depending on the energy sources used for the synthesis of organic substances in the cell, are divided into two groups: phototrophs and chemotrophs.
Phototrophs include terrestrial green plants, algae, phototrophic bacteria capable of photosynthesis. The most important in the production of organic matter on the planet belongs to terrestrial green plants that use solar energy through the reaction of photosynthesis.
From a chemical point of view, the process of photosynthesis involves fixing some of the sunlight as potential or "bound" energy. The redox reactions of photosynthesis involving solar energy can be summarized by the following equation:
nCO2 + 2nH2O_solar energy_____________________(CH2O)n + nO2
In green plants, water is oxidized to release gaseous oxygen, and carbon dioxide is reduced to carbohydrates (CH2O)n to release water. Higher plants have different biochemical pathways for CO2 recovery, which is also important in ecology: the physiological and morphological characteristics of plants, their distribution, adaptability to various environmental conditions, and productivity are associated with this.
Most plants fix CO2 through the C3 pentophosphate pathway, or Calvin cycle. Some plants reduce carbon dioxide through the C4-dicarboxylic acid cycle. These plants have a specific morphological difference: they have large chloroplasts in the lining of the passing bundles (around the leaf veins).
Depending on which cycle the synthesis of organic compounds is carried out, and in accordance with the nature of the ongoing processes of photosynthesis, C3 or C4 plants are isolated.
I Opt II Opt III Opt
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Activity (growth) Temperature
Rice. 2.2 Dependence of changes in the intensity of photosynthesis in C3- and C4-plants on illumination and temperature (according to Yu. Odum, 1975): I - C3-plants; II - the range of existence of plants; III - C4 - plants.
Comparison of the response of C3 and C4 plants to light shows (Fig. 2.2) that C3 plants usually have the maximum intensity of photosynthesis at moderate light and temperature; high temperatures and light inhibit photosynthesis. C4 - plants are adapted to bright light and high temperature and under these conditions significantly outperform C3 plants. They also use water more efficiently: for the production of 1g. dry matter they need less than 400g. water, and C3 plants - from 400 to 1000g. In addition, C4 plants are also not inhibited by excess oxygen (unlike C3 plants).
C4 plants predominate among desert and steppe vegetation, in warm and tropical climates, in sparse forests, and also in the north, where light and temperature are low. Among them, plants of the cereal family (corn, sorghum) predominate, but there are also some others (for example, sugarcane).
Although the photosynthesis efficiency per unit leaf area is lower in C3 plants than in C4 plants, they account for the majority of photosynthetic production on Earth. This is apparently due to the better adaptability of plants with this type of photosynthesis to existence in mixed communities, where light, temperature, and other factors are closer to average values.
C3 plants also include the vast majority of plants from which a person receives food - rice, wheat, potatoes, vegetables. They grow mainly in the temperate zone of the northern hemisphere.
In contrast to green plants, inorganic sulfur compounds serve as an electron donor in purple and green sulfur bacteria during photosynthesis, and oxygen is not released:
CO2 + H2S ____light___________(CH2O)n + S
Cyanobacteria, like higher plants and algae, release molecular oxygen during photosynthesis.
Globally, the contribution of phototrophic microorganisms to the synthesis of organic matter is small. But they can live in conditions unfavorable for most green plants and play important role in the circulation of certain substances. For example, green and purple sulfur bacteria play a significant role in the sulfur cycle. Phototrophic microorganisms are found in sediments or waters - where little light penetrates. Bacterial photosynthesis can be beneficial in polluted and eutrophic waters. For this reason, interest in him is now increasing. But it cannot replace plant photosynthesis, on which the life of complex aerobic organisms on Earth depends.
Chemotrophs- microorganisms that assimilate organic compounds by chemosynthesis. The process of synthesis of organic matter is carried out due to the energy obtained by the oxidation of ammonia, hydrogen sulfide and other substances. Chemosynthetic organisms include sulfur bacteria (for example, Thiobacillus species that oxidize hydrogen sulfide), nitrifying bacteria (species of the genera Nitrosomonas, Nitrosospira, Nitrosococcus, converting ammonia into nitrites and then into nitrates), and others. Chemotrophs play a small role in the primary production of organic matter, but they are important in the circulation of chemical elements on the planet.
For the functioning of the ecosystem, not only the synthesis of organic matter is equally important, but also its decomposition, which is carried out by heterotrophs.
heterotrophic organisms- organisms that use organic substances synthesized by other organisms as energy and a source of nutrition. These include all animals, fungi, most bacteria, and non-chlorophyll land plants and algae. In ecosystems, heterotrophic organisms are divided into consumers and decomposers.
Consumers(from lat. Consumo - I consume) - consumers of organic matter produced by autotrophs. They are divided into consumers of the first order (herbivorous animals), second, third, etc. (predators).
decomposers(from Latin Reducentis - returning, restoring) - organisms that feed on dead organic matter and subject it to mineralization to more or less simple compounds, which are then used by producers. Decomposers are mainly bacteria and fungi. Depending on which organisms decompose organic matter and under what conditions, two processes are distinguished: respiration (aerobic and anaerobic) and fermentation.
Aerobic respiration proceeds in the presence of atmospheric oxygen, which serves as an electron acceptor (oxidizing agent).
Aerobic respiration can be compared to the reverse process of photosynthesis, that is, it is aimed at the decomposition of synthesized organic matter into carbon dioxide and water with the release of energy. With the help of this process, higher plants and many animal species receive energy to maintain the vital activity of building new cells of their own body. However, the process of aerobic respiration may not go to the end, and as a result of such incomplete respiration, organic compounds are formed that contain a certain amount of energy, which can later be used by other organisms.
Anaerobic respiration serves as the basis for the vital activity of mainly saprophytes (bacteria, yeast, mold fungi, protozoa), although this process can also occur in some tissues of higher plants. For example, methane bacteria decompose organic compounds, producing methane (CH4) by reducing organic carbon.
Fermentation- the process of anaerobic enzymatic breakdown of organic matter by various microorganisms, in which the released energy is used for the biosynthesis of various vital amino acids and proteins. During fermentation, the oxidizable organic compound itself serves as an oxidizing agent (electron acceptor).
An example of fermentation is the processes that take place with the participation of yeast. They are of practical value to humans, participate in the processes of soil formation (decomposition of plant residues).
Many groups of bacteria are capable of both aerobic and anaerobic respiration, but the end products of these two reactions are different and the amount of energy released during anaerobic respiration is much less.
Despite the fact that anaerobic saprophages play an inconspicuous role in the community, they are important for the ecosystem, since they are the only ones capable of respiration in oxygen-free soil layers and underwater sediments deprived of light. They intercept energy and substances, which then diffuse upward and become available to aerobes.
Reduced organic and inorganic compounds synthesized by microorganisms under anaerobic conditions serve as a carbon reserve for fixing energy in the process of photosynthesis. Later, under aerobic conditions, these reduced compounds are used as a substrate by aerobic chemolithotrophs and heterotrophs. Consequently, anaerobic and aerobic organisms are closely interconnected and functionally complement each other.
In terms of species diversity, heterotrophs are significantly superior to autotrophs and can exist in a wide variety of conditions. Together, heterotrophs are able to decompose all substances synthesized by autotrophs, including many compounds synthesized by humans using various technologies. Their role in the biosphere is to decompose the synthesized organic matter into simpler compounds, thereby supporting the circulation of chemical elements in nature.
A common feature of all ecosystems is the interaction of autotrophic and heterotrophic components. Organisms involved in various cycle processes are separated in space: autotrophic processes are most active in the upper layer, where sunlight penetrates, heterotrophic processes occur in the lower layer, where organic matter accumulates in soils and sediments.
It should be noted that the main functions of the ecosystem components partially do not coincide in time. This is due to the fact that there is a certain time gap between the production of organic matter by autotrophic organisms and its consumption by heterotrophs. For example, the main process in the forest canopy is photosynthesis. After photosynthesis of organic matter, only a small part of it
The composition of the ecosystem includes living organisms (their totality is called biocenosis, or biota, ecosystems), factors inanimate nature(abiotic) - atmosphere, water, nutrients, light and dead organic matter - detritus.
All living organisms are divided into two groups according to the method of nutrition (according to the functional role) - autotrophs (from the Greek words autos - itself and tropho - nutrition) and heterotrophs (from the Greek word heteros - another).
Autotrophs.
These organisms use inorganic carbon for the synthesis of organic matter; these are the producers of the ecosystem. According to the energy source used, they, in turn, are also divided into two groups.
Photoautotrophs use light. These are green plants, cyanobacteria, as well as many colored bacteria that have chlorophyll (and other pigments) and absorb solar energy. The process by which it is digested is called photosynthesis.
Chemoautotrophs use the chemical energy of the oxidation of inorganic substances (sulfur, hydrogen sulfide, ammonia, iron, etc.). These are sulfur bacteria, hydrogen bacteria, iron bacteria, nitrifying bacteria, etc. Chemoautotrophs play leading role in groundwater ecosystems, as well as in special ecosystems of rift zones of the ocean floor, where hydrogen sulfide is released from plate faults, which is oxidized by sulfur bacteria. Nitrifying bacteria play an important role in terrestrial ecosystems.
Heterotrophs. These organisms feed on ready-made organic substances that are synthesized by producers, and together with these substances they receive energy. Heterotrophs in the ecosystem are consumers (from the Latin word consumo - I consume), consuming organic matter, and decomposers, decomposing it into simple compounds. There are several consumer groups.
Phytophages (herbivores). These include animals that feed on living plants. Among phytophages there are both small organisms, such as aphids or grasshoppers, and giants, such as elephants. Almost all agricultural animals are phytophages: cow, horse, sheep, rabbit. The main phytophages in aquatic ecosystems are microscopic organisms of herbivorous plankton that feed on algae. There are also large phytophages in these ecosystems, for example, grass carp, eating plants that overgrow irrigation canals. An important phytophage is the beaver. It feeds on tree branches, and from the trunks it builds dams that regulate the water regime of the territory.
Zoophages (predators, carnivores). Zoophages are very diverse. These are small animals that feed on amoebas, worms or crustaceans. And big ones, like a wolf. Predators that feed on smaller predators are called second-order predators. Filter-feeding zoophages are widespread in aquatic ecosystems, this group includes microscopic crustaceans and whales. Filter feeders play a huge role in the self-purification of polluted waters (Fig. 30). Only planktonic marine copepods from the genus Calanus are able to filter the waters of the entire World Ocean in a few years!
There are predatory plants (dew, pemphigus) that use insects as food. True, their way of feeding differs from animal predators. They “catch” small insects, but do not swallow them, but “digest” them, releasing enzymes on their surface. There are also predators among soil fungi that "catch" microscopic round nematode worms.
Symbiotrophs. These are bacteria and fungi that feed on the root secretions of plants. Symbiotrophs are very important for the life of the ecosystem. Threads of fungi that entangle the roots of plants help the absorption of water and minerals. Symbiotrophic bacteria absorb gaseous nitrogen from the atmosphere and bind it into compounds available to plants (ammonia, nitrates). This nitrogen is called biological (in contrast to the nitrogen of mineral fertilizers).
Symbiotrophs also include microorganisms (bacteria, unicellular animals) that live in the digestive tract of phytophagous animals and help them digest food. Animals such as cows, without the help of symbiotrophs, are not able to digest the grass they eat.
Detritophages are organisms that feed on dead organic matter. These are centipedes, earthworms, dung beetles, crayfish, crabs, jackals and many others. A significant diversity of detritivorous species is associated with the soil. There are numerous detritophages that destroy wood (Fig. 31).
Organisms that feed on feces are called coprophages. Some organisms eat both plants and animals and even detritus and are euryphages (omnivores) - bear, fox, pig, rat, chicken, crow, cockroaches. Euryphage is also a man.
Decomposers are organisms that, by their position in the ecosystem, are close to detritophages, since they also feed on dead organic matter. However, decomposers - bacteria and fungi - break down organic matter to mineral compounds, which return to the soil solution and are again used by plants.
Decomposers need time to process dead organic matter. Therefore, in the ecosystem there is always a reserve of this substance - detritus. Detritus is leaf litter on the surface of forest soil (remains for 2–3 years), the trunk of a fallen tree (remains for 5–10 years), soil humus (remains for hundreds of years), deposits of organic matter on the bottom of the lake - sapropel and peat in the swamp (remains thousands years). The longest lasting detritus are coal and oil.
Producers, phytophages, predators are connected in the process of ecosystem "work", that is, the assimilation and expenditure of energy in the production of organic matter and, as it were, participate in the "relay race" of energy transfer. The number of the relay participant is his trophic level. The first trophic level - producers, the second - phytophages, the third - predators of the first order, the fourth - predators of the second order. In some ecosystems, for example in a lake, the number of trophic levels can reach 5-6.
On fig. 32 shows the structure of the ecosystem, which is based on plants - photoautotrophs, and in table. 1 shows examples of representatives of different trophic groups for some ecosystems.
Table 1
Representatives of different trophic groups in some ecosystems
Trophic group Ecosystem Forest Reservoir Agricultural land Producers Spruce, birch, pine Algae, pondweed, water lily, duckweed Wheat, rye, potatoes, thistle Thistle plant-eating consumers Elk, hare, squirrel, gypsy moth, aphid
muskrat, silver carp Human, cow, sheep, mouse, vole, weevil, aphid Consumers-zoophages Wolf, fox, polecat, woodpecker, ants Cyclops crustaceans, gull, perch, ide, pike, catfish Human, starling, ladybug Consumers-detritophages Dead-eater beetle, kivsyak, earthworm Perlovitsa, bloodworm, daphnia Larvae of beetles and flies earthworm
test questions
1. In what ecosystems do chemoautotrophs play an important role?
With the population approach, the ecologist sets the task of finding out the reasons that explain the distribution of populations in space, their size, dynamics, and other features. With the ecosystem approach, the researcher faces a more difficult task - to study the processes of transformation of matter and energy flows in the ecosystem, which occur with the participation of organisms.
Chapter 10 Ecosystem Concept
R. Lindeman (Lindeman, 1942) considered an ecosystem as "... a system of physico-chemical-biological processes occurring within a certain spatio-temporal unit of any rank." Despite this functional orientation of the ecosystem approach, great importance has the study of the species composition of ecosystems and their spatial and temporal structure. These external signs reveal the essence of the processes of transformation of matter and energy.
10.1. Ecosystem Definition
The concept of "ecosystem" was proposed by A. Tensley in 1935, however, as A.M. Gilyarov, “... there is no clear generally accepted definition of an ecosystem, but it is usually considered that it is a collection of different organisms living together, as well as physical and chemical components of the environment that are necessary for their existence or are products of their vital activity” (1990, p. 5).
To date, there are two understandings of the ecosystem: narrow and broad.
With a narrow (traditional) understanding as ecosystems, only such sets of organisms and environmental conditions are considered in which there is a self-regulation regime. With this understanding, ecosystems include natural forests, lakes, swamps, seas, etc. If these ecosystems are disturbed (of course, up to a certain limit), then they will restore themselves, if not in the previous composition, then, in any case, close to the previous one. The narrow scope of the concept of an ecosystem is primary and is rooted in the ideas of A. Tansley.
In a broad sense (Odum, 1986), ecosystems include any combination of interacting organisms and their habitat conditions, regardless of whether they have a self-regulation mechanism or not. In this case, a city, an agricultural farm, a forest plantation, a spacecraft cabin, etc. can be considered as an ecosystem. The textbook takes a broad understanding of the ecosystem as more convenient.
The ecosystem has no territorial rank. Ecosystems can include an anthill, a ravine, a lake, a mountain range, the Pacific Ocean, the Eurasian continent, and the biosphere. It is possible to build a hierarchy of ecosystems: within a large ecosystem, ecosystems of lower ranks can be distinguished. For example, within the boundaries of the urban ecosystem, ecosystems of a residential area, a forest park, and large enterprises are distinguished.
We should specifically dwell on the relationship between the concepts of "ecosystem", "biogeocenosis" and "landscape". They have a "parallel circulation" in science and their scope overlaps. The concept of "biogeocenosis" in 1942 was proposed by V.N. Sukachev initially, as opposed to the concept of "ecosystem", which, in accordance with the mentality of science of that time, was considered bourgeois. However, over time, it became obvious that the concept of "biogeocenosis" cannot replace the concept of "ecosystem". If an ecosystem is a non-ranking concept, then a biogeocenosis has a certain rank: it is a homogeneous area of a terrestrial (but not aquatic!) ecosystem, the boundaries of which are drawn along the boundaries of a phytocenosis, which acts as a marker of this unit.
The geographical landscape also corresponds to an ecosystem of a certain rank - a fairly large homogeneous geographical unity (with one type of relief and climate, a regular combination of soils and vegetation), within which more fractional ecosystem units are distinguished - tracts ("sublandscapes") and facies (corresponding to biogeocenoses).
A certain rank of the ecosystem is the concept of "natural-territorial complex" (NTC) widely used in Russian geography.
test questions1. What distinguishes the ecosystem approach in ecology from the population approach?
2. Tell us about the narrow and broad interpretation of the concept of "ecosystem".
3. What is the ratio of the volumes of the concepts "ecosystem", "biogeocenosis", "geographical landscape", "tract", "facies", "PTK"?
10.2. Functional blocks of the ecosystem
Despite the fact that there can be thousands of species in an ecosystem, according to their functional role, these species can be combined into a limited number of functional types - producers, consumers, and decomposers, which ALavoisier distinguished (without using these terms). These types are textbooks and therefore we confine ourselves to their brief description.
Producers are autotrophs, i.e. organisms that synthesize organic substances from inorganic carbon.
Plants are photoautotrophic producers. In addition, cyanobacteria also play an important role in the ocean. Photoautotrophs carry out photosynthesis from carbon dioxide and water with the release of oxygen using solar energy. This diverse group of organisms includes giants like sequoia and eucalyptus, and microscopic planktonic algae, which are the main producers of aquatic ecosystems. Cyanobacteria are also capable of fixing atmospheric nitrogen. There are also photoautotrophic producers that carry out photosynthesis without oxygen release (purple bacteria), but their overall contribution to the biological production of the ecosystem is small.
Producers - chemoautotrophs(sulfur bacteria, methanobacteria, iron bacteria, nitrifying bacteria, etc.) for the synthesis of organic substances use the chemical energy of the oxidation of inorganic compounds. These organisms are producers of ecosystems in hydrothermal oases, formed in the so-called rift zones of the ocean - areas of fracture of the earth's crust, hydrogen sulfide is released from cracks formed between plates, and in groundwater ecosystems. They play an important role in the biogeochemical transformation of the earth's crust (they live in groundwater at a depth of 3-5 km). This group also includes soil nitrifying bacteria that oxidize ammonium and nitrite.
Consumers - these are organisms that use ready-made organic matter in a living or dead state. This block includes the following functional groups.
Phytophages - herbivorous organisms. This diverse group in terrestrial ecosystems includes taxa ranging from insects (such as termites, which are the main phytophages in rainforests) to large mammals like elk, giraffe and elephant. In aquatic ecosystems, the main phytophages are small zooplankton organisms (the so-called herbivorous plankton).
Zoophages - predators. Like phytophages, zoophages range from large (lion, wolf) to microscopic (zooplankton crustaceans). Predators are divided into typical predators that kill the prey (for example, a wolf or a falcon), and predators with a pasture type of food, which, without killing the prey, use it for a long time (for example, gadflies, horseflies).
Symbiotrophs - microorganisms (fungi, bacteria, unicellular protozoa) that are associated with mutually beneficial cooperation with plants or animals (mycorrhiza fungi, nodule bacteria of legumes, bacteria and protozoa (amoebas) of the digestive tract of mammals, including humans). They feed on intravital secretions of organisms (in plants) or participate in digestion (in animals).
Detritivores- These are animals that feed on detritus (dead tissues of plants and animals or excrement). The diversity of these organisms was discussed in section 8.7.
decomposers(destructors) are bacteria and fungi that, during their vital activity, convert organic residues into inorganic substances, ensuring the return of the elements contained in them to the soil solution or to water (in aquatic ecosystems), from where they are re-consumed by plants. Thanks to reducers, most of the carbon dioxide consumed in the process of photosynthesis returns to the atmosphere, and methane is also formed during the anaerobic decomposition of organic matter under conditions of high humidity.
The division of organisms that feed on dead organic matter (saprotrophs) into detritivores and decomposers is conditional. So, up to 40% of the bacteria of aquatic ecosystems that form bacterial plankton are eaten in a living state, i.e. are not decomposers, but detritivores. They do not supply resources for plants, but are themselves a food resource for consumers of the next trophic level (i.e., detrital food chains start from them).
Animals-detritophages, crushing organic residues, facilitate the "work" of decomposers and thereby participate in the process of decomposition of organic matter. Finally, any detritophage is also a “predator”, because, according to M. Bigon, “it feeds on dry biscuits smeared with peanut butter” (consumes dead organic matter along with living bacteria that have settled on it).
test questions1. Describe the main functional types of organisms that make up the ecosystem.
2. Tell us about the diversity of consumers.
3. What is the difference between typical predators and pasture predators?
3. What is the conditionality of the division of detritivores and decomposers, detritivores and predators?
10.3. Ecosystem classification
With a wide scope of the concept of "ecosystem", it becomes generic, within which several types (types) of ecosystems are established, differing in the source of energy and functional structure, as well as in the contribution of humans to their organization (Table 9).
Table 9 Ecosystem classification
According to the type of energy supply and carbon source, ecosystems are divided into autotrophic And heterotrophic. The composition of autotrophic ecosystems includes producers that provide matter and energy to the heterotrophic biota of the ecosystem. There are no producers in the composition of heterotrophic ecosystems, or they play an insignificant role, and organic substances enter them from outside. Thus, the existence of heterotrophic ecosystems always depends on the activity of autotrophic ecosystems, since there can be no other organic matter than that produced by organisms of autotrophic ecosystems. This organic matter can be detritus, representing the biological products of not only modern ecosystems, but also ecosystems that existed in the distant past (coal, oil, gas).
However, this division is rather arbitrary. There are autotrophic-heterotrophic ecosystems. In these ecosystems, along with solar energy and inorganic carbon used by producers, a significant role is played by energy fixed in “ready” organic matter coming from outside (for example, ecosystems of small forest lakes into which leaves and other forest detritus fall; lakes into which organic matter comes in with effluents).
The division of ecosystems into natural And artificial (anthropogenic), man-made is also relative. For example, an intensively used pasture is both natural and artificial: grazing-resistant species have been selected from a natural meadow or steppe ecosystem, but under the influence of human activities. Man even influences protected ecosystems, which receive their share of acid rain and other pollutants that are transported in the atmosphere over long distances.
test questions1. Explain the content of the main approach for classifying ecosystems by energy source and human role.
2. Give examples of ecosystems that represent the transition from natural to anthropogenic.
3. Give examples of natural heterotrophic ecosystems.
4. Describe the diversity of anthropogenic ecosystems.
5. Give examples of ecosystems that represent the transition from autotrophic to heterotrophic.
10.4. Energy in an ecosystem. food chains
The basis of the "work" of the ecosystem is made up of two related processes: the circulation of substances, which is carried out due to the activities of producers, consumers and decomposers, and the flow of energy through it coming from outside. Energy is used once and is spent on "untwisting" the circulation of substances. The cycles of substances in a particular ecosystem and the biosphere are of a similar nature, and therefore we will consider them in Chapter 13. In this section, we will get acquainted with the patterns of energy flow through an ecosystem.
Physicists define energy as the ability to do work or heat exchange between two objects that have different temperatures. Energy is the basis of the “work” of any ecosystem in which synthesis and multiple transformations of substances take place.
The main source of energy is the Sun. Even heterotrophic ecosystems use solar energy, albeit through an intermediary, which is an autotrophic ecosystem that supplies organic matter for it. Y. Odum (1986) even defined ecology as a science that "... studies the relationship between light and ecological systems and ways of converting energy within an ecosystem" (p. 106).
The flow of solar energy constantly flows through photoautotrophic organisms, and when energy is transferred from one organism to another in food chains, it is dissipated in the form of heat. No more than 2% of the solar energy coming to Earth is absorbed by the ecosystem (in experimental cultures of marine planktonic algae, it was possible to achieve a level of solar energy fixation of 3.5%). Most of the energy is used for transpiration, reflected by leaves, and used to heat the atmosphere, water and soil (see 2.2.2).
The sequence of organisms in which each previous organism serves as food for the next one is called food chain. Each link in this chain is trophic level(plants, phytophages, predators of the 1st order, predators of the 2nd order, etc.).
There are two types of food chains: pasture (autotrophic), in which plants act as the first link ( grass - cow - man; grass - hare - fox; phytoplankton - zooplankton - perch - pike, etc.), and detrital (heterotrophic), in which the first link is represented by dead organic matter, which feeds on detritophage (fallen leaf - earthworm - starling - falcon).
The number of links in food chains can be from one or two to five or six. Food chains in aquatic ecosystems tend to be longer than in terrestrial ones.
Since most organisms have a broad diet (i.e., they can eat organisms of different species), in real ecosystems, food chains do not function, but food webs. For this reason, the food chain is a simplified expression of the trophic relationships in an ecosystem.
The efficiency of energy transfer along the food chain depends on two indicators:
1. from the completeness of grazing (the proportion of organisms of the previous trophic level that were eaten alive);
2. on the efficiency of energy assimilation (the specific share of energy that has passed to the next trophic level in terms of each unit of biomass eaten).
The completeness of grazing and the efficiency of energy assimilation increase with an increase in the trophic level and vary depending on the type of ecosystem.
Thus, in the forest ecosystem, phytophages consume less than 10% of plant production (the rest goes to detritophages), and up to 30% in the steppe. In aquatic ecosystems, the grazing of phytoplankton by herbivorous zooplankton is even higher, up to 40%. This explains the main colors of the Earth in satellite images: forests are green precisely because phytophages eat little phytomass, and the ocean is blue because phytophages eat a lot of phytoplankton (Polis, 1999).
When assessing the energy absorption coefficient in food chains, the “Lindemann number” is often used: on average, 10% of energy is transferred from one trophic level to another, and 90% is dissipated. However, this "number" oversimplifies and even distorts the real picture. The "Law of 10%" is valid only when energy moves from the first trophic level to the second, and even then not in all cases. The efficiency of energy assimilation in the next links of the food chain - from phytophages to zoophages or to predators of higher orders - can reach 60%.
The high efficiency of energy absorption in the "carnivorous" links of food chains explains the relatively small amount of excrement of predators and the limited composition of saprotrophs (decomposers, coprophages) that feed on them. The main fauna of coprophages is associated with the excrement of herbivorous animals. By the way, everyone knows from personal experience that with predation the efficiency of energy absorption is higher than with phytophagy: a vegetarian dinner of vegetables or potatoes is large in volume, but low in calories, and a relatively small steak will satisfy hunger and provide a feeling of satiety for a long time.
Thus, in the food chain at each next trophic level, the relative amount of energy transferred increases, since both the consumption of living biomass and its assimilation increase simultaneously (the proportion of biomass that returns to the ecosystem with excrement decreases).
The behavior of energy is subject to the action of the first and second laws of thermodynamics.
The first law (conservation of energy) - about the preservation of its quantity during the transition from one form to another. Energy cannot appear in an ecosystem by itself; it enters it from the outside with sunlight or as a result of chemical reactions and is absorbed by producers. Further, it will be partly used by consumers and symbiotrophs, "serving" plants, partly by decomposers, which decompose dead parts of plants, and partly spent on respiration. If we sum up all these fractions of the energy consumption, assimilated by plants in a photoautotrophic ecosystem, then the sum will be equal to the potential energy accumulated during photosynthesis.
The second law is about the inevitability of energy dissipation(i.e., reducing its “quality”) when moving from one form to another. In accordance with this law, energy is lost during its transfer through food chains. In the most general form, these losses reflect the "Lindemann number".
test questions1. What is energy?
2. How much solar energy can an ecosystem absorb?
3. What is a food chain?
4. What is a trophic level?
5. Give examples of grazing and detrital food chains.
6. What is the number of links in food chains in terrestrial and aquatic ecosystems?
7. What is the difference between the concepts of "food chain" and "food web"?
8. To what extent does the completeness of grazing of organisms change at different trophic levels and in different ecosystems?
9. How does the efficiency of energy absorption by organisms change with an increase in their trophic level?
10. Illustrate the operation of the laws of thermodynamics in the "work" of the ecosystem.
10.5. Detritus in the ecosystem
Detritus- dead organic matter, temporarily excluded from the biological cycle of nutrients. The retention time of detritus can be short (corpses and excrement of animals in a warm climate are processed by fly larvae in a few days, leaves in the forest - in a few months, tree trunks - in a few years) or very long (humus, sapropel, peat, coal, oil) .
Detritus is a reservoir of nutrients in an ecosystem, a necessary component of its normal functioning. As already noted, there are special organisms - detritophages that feed on detritus.
Consider the main types of detritus.
Humus - dark-colored soil organic matter, which is formed as a result of biochemical decomposition of plant and animal residues and accumulates in the upper (humus) soil horizon. Most of the humus (85-90%) is represented by humic substances proper - humin, fulvic acids, humic acids, etc., the rest - by less decomposed plant and animal remains. The carbon content in humus is about 50%. The amount of humus is maintained by two oppositely directed microbiological processes - humification (the anaerobic process of converting animal and plant remains into humus) and mineralization (the aerobic process of breaking down humus into simple organic and mineral compounds). In the soils of natural ecosystems, these processes are in balance, and the humus content in the soil is maintained constant. Humus is the basis of soil fertility.
With human intervention (for example, when plowing the soil), mineralization processes begin to predominate, which leads to a decrease in the humus content and the release of carbon dioxide into the atmosphere, which makes a significant contribution to the enhancement of the greenhouse effect (see 13.2.1).
Different types of soils differ in humus content and thickness of the humus horizon. Chernozems are the richest in humus, its content in these soils can reach 10% (in the past in some regions of the Russian Federation and Ukraine it reached 16%), and the thickness of the humus horizon is 1 m. Podzolic and chestnut soils are the poorest in humus. The thickness of their humus horizon is 5–15 cm, and the humus content is 1–2%. The transitional position between podzolic soils and chernozems is occupied by gray forest soils, and between chernozems and chestnut soils, dark chestnut soils. In the chestnut brown desert soils located to the south, the humus content is less than 1%. The soils of wet habitats are very rich in humus - meadow and wet meadow.
In different types of soils, humus differs in mobility: the humus of chernozems is most difficult to mineralize (V.V. Dokuchaev called chernozems a “stingy knight” for this), and most easily in the soils of tropical rainforests. The stock of humus in tropical soils is small (the thickness of the humus horizon is several centimeters, and the content of humus in it is no more than 4%), nevertheless, due to the rapid circulation of substances, these ecosystems provide high biological production (see 10.6).
Forest floor - a layer of detritus on the surface of forest soil, formed mainly by fallen leaves and tree twigs. Litter plays an important role in the life of the forest ecosystem. The litter contains a significant number of detritivorous species, as well as decomposers, represented mainly by fungi. The litter absorbs moisture from rains and melting snow, which reduces surface water runoff, and in mountain forests reduces the likelihood of soil erosion. The litter acts as a filter that retains substances contained in the water (fertilizer residues, pesticides, heavy metals, etc.). For this reason, the water of forest springs is always quite clean. In terms of its role in the ecosystem, it is close to the forest floor rag- dry shoots of plants in the steppe (steppe felt).
The ratio of the mass of the forest floor (or rags in grass communities) to the annual fall of leaves and branches serves as an indicator of the detritus decomposition rate. The higher this index, the lower the intensity of the circulation of substances. The stock of litter (t/ha) and the index of its decomposition rate (years) are: 44 (50) in tundra, 14 (10–17) in taiga, 14 (3–4) in deciduous forests, and 3 (3) in savanna 1), in the steppe - 3 (2), in tropical rainforests - 3 (0.1).
Peat - these are poorly decomposed plant remains that accumulate in the swamp ecosystem. Under a microscope, it is not difficult to identify the plant remains of the species that formed the peat. Bogs of different types form peat of varying degrees of richness in mineral and organic substances. The peat of low-lying bogs is the richest in minerals, the peat of raised bogs is the poorest.
Bottom sediments(sapropel) - sediments at the bottom of continental water bodies, which consist of organic residues mixed with mineral sediments. Unlike humus, which is constantly involved in the cycle of substances in the ecosystem, bottom sediments are a rather conservative formation, only their uppermost part, a layer no more than 5 cm thick, participates in the cycle, and the rest of the detritus is practically excluded from the cycle. This, by the way, explains the phenomenon of self-purification of water bodies: pollutants, having fallen to the bottom with dead plankton, are buried there and are not involved in the circulation. Significant accumulation of organic matter at the bottom of lakes occurs only where an anaerobic zone is created, in which bacteria consume all oxygen and the rate of mineralization of organic matter decreases sharply. The more productive the ecosystem is, the more likely it is that an oxygen deficiency will occur in water (see 11.1).
At the bottom of reservoirs created on rivers heavily polluted by cities and industrial enterprises, huge masses of toxic precipitation are “conserved”, which, by the way, serves as the main argument against the liquidation of these reservoirs.
test questions1. What role does detritus play in an ecosystem?
2. List the main forms of detritus.
3. How does the humus content change in different soils?
4. What is the functional role of the litter in the forest ecosystem?
5. What factors contribute to the accumulation of bottom sediments?
10.6. Biological products and biomass stock
Biological products - the rate of accumulation of biomass in an ecosystem, which reflects the ability of organisms to produce organic matter in the course of their life activity.
Biological production is measured by the amount of organic matter created per unit of time per unit area (t/ha/year, kg/sq. m/year, g/sq. m/day, etc.).
Distinguish primary(created by plants and other autotrophs) and secondary(created by heterotrophs) biological products. The composition of primary products varies gross(i.e. total production of photosynthesis) and clean biological products - "profit" that remains in plants after the costs of respiration and the release of organic matter from the roots into the soil (these substances are used by symbiotrophs) and phytoplankton algae into the water (these substances are absorbed by bacteria).
The ratio of gross and net primary biological production depends on the favorable environmental conditions: the better the conditions, the lower the cost of breathing and the maintenance of "service personnel". Under favorable conditions, net production can be up to 50% of the gross, in unfavorable conditions - 5-10% (Rakhmankulova, 2002).
R. Whittaker (1980) divides ecosystems into four classes according to primary biological production (in dry matter):
- very high (over 2 kg / m 2 per year). Such production is typical for tropical rainforests, coral reefs, geothermal "oases" of deep ocean rift zones, floodplains - high and dense reed beds in the Volga, Don and Ural deltas;
- high (1–2 kg / m 2 per year). These are linden-oak forests, coastal thickets of cattail or reeds on the lake, crops of corn and perennial grasses, if irrigation and mineral fertilizers are used;
- moderate (0.25–1 kg / m 2 per year). The predominant part of agricultural crops, pine and birch forests, hay meadows and steppes, lakes overgrown with aquatic plants, "sea meadows" of algae;
- low (less than 0.25 kg / m 2 per year). These are deserts of a hot climate, arctic deserts of the islands of the Arctic Ocean, tundra, semi-deserts of the Caspian Sea, steppe pastures trampled down by cattle with low and sparse herbage, stony steppes. Most of the marine ecosystems in the pelagic zone have the same low production (see 11.2).
The average biological production of the Earth's ecosystems does not exceed 0.3 kg/m 2 per year, since the planet is dominated by low-productive ecosystems of deserts and oceans.
Biomass - this is the stock (quantity) of living organic matter (plants, animals, fungi, bacteria), the "capital" of the ecosystem, which is divided into phytomass (mass of plants), zoomass (mass of animals), microbial mass. The average biomass per unit land area is 0.5 kg/ha.
The main chemical element in biomass is carbon, 1 g of organic carbon corresponds to an average of 2.4 g of dry biomass. In biomass, for every 100 parts of carbon, there are 15 parts of nitrogen and 1 part of phosphorus. However, the ratio of carbon and nitrogen differs in the biomass of animals and plants, which explains their different quality as a food resource (see 2.2.1).
In addition to carbon, nitrogen and phosphorus, biomass contains a lot of oxygen, hydrogen and sulfur. (Remember the word "CHNOPS", see 2.2.1.)
Since the life span of different organisms is different, the biomass can be more than annual production (in forests - 50 times, in the steppe - 3-5 times), equal to it (in communities of cultivated annual plants) or less (in aquatic ecosystems dominated by short-lived plankton organisms that give several generations per year).
Typically, plant biomass is greater than animal biomass, although there are exceptions to this rule. For example, in water bodies, the mass of zooplankton can be greater than the mass of phytoplankton, since the life of phytoplankton algae is shorter than the life of zooplankton organisms (up to 4 generations of algae can change during the life of a plankton crustacean).
The ratio of the biomass of different trophic levels is reflected in ecological pyramids. Biomass pyramids of terrestrial ecosystems always have a wide base and narrow with increasing trophic levels. Pyramids of the biomass of aquatic ecosystems can be shaped like a spinning top (Fig. 20): the maximum biomass is concentrated in the average trophic level of zooplankton, whose organisms live longer than unicellular phytoplankton algae. At higher levels of nekton (fish), a decrease in biomass also occurs.
Rice. 20. Ecological pyramids of biomass of terrestrial and aquatic ecosystems.
In the structure of biomass, the biomass of the aboveground and underground parts of the ecosystem is distinguished. In most ecosystems, the underground plant biomass exceeds the aboveground one, and in meadow communities 3–10 times, in steppe communities 30–50 times, in desert communities 50–100 times. The exception is forests, where above-ground biomass significantly exceeds below-ground biomass. The underground biomass of animals is always many times greater than the aboveground biomass. In agrocenoses, aboveground and belowground biomass can be approximately equal, while in forests, aboveground biomass exceeds belowground.
The cycle of organic matter in the biosphere occurs on average for 4 years. In different ecosystems, this indicator varies greatly: in aquatic ecosystems, the cycle occurs 1000–2000 times faster than in the forest.
test questions1. What are primary and secondary biological products?
2. How does the value of primary and secondary biological production differ in different ecosystems?
3. To what extent does the biological production of different ecosystems change?
4. What is the average value of the biological production of the Earth's ecosystems?
5. Compare the concepts of "biological products" and "biomass".
6. How does the ratio of biological products and biomass change in different ecosystems?
7. What is the average chemical composition of the planet's biomass?
8. What is an ecological pyramid? What variants of ecological pyramids do you know?
9. Compare the ecological pyramids of terrestrial and aquatic ecosystems.
10. How fast is the cycle of biomass in different ecosystems?
10.7. Composition of biota (biodiversity) of an ecosystem
Despite the fact that for an ecologist, an ecosystem is primarily a functional phenomenon, which is assessed by the intensity of the energy flow flowing through it, the nature of the cycles of substances, the magnitude of biological production (primary and secondary), an important role is played by the study of biota - the living population of the ecosystem, which ultimately reflects its function.
The biota of most ecosystems has a complex composition, represented by a large number of different taxa. For example, the biota of terrestrial ecosystems includes plants (lower and higher), a huge variety of animal species, fungi and bacteria. In principle, this diversity can be taken into account, but no one has ever done this. To carry out a complete inventory of the biota of only one ecosystem, it will be necessary to involve several dozen specialists in various taxa of plants (mosses, spore vascular, gymnosperms, flowering plants), fungi, lichens, animals (different groups of protozoa, insects, birds, mammals, etc.) .), bacteria. The result of the work of such a scientific team will be very expensive, and its scientific significance will be low (since it will be nothing more than an illustration representing just one of the ecosystems). The cost of studying many ecosystems to identify common patterns in the relationship of biodiversity with environmental conditions will be unrealistically high.
Usually, the biodiversity of an ecosystem is determined approximately by the number of plant species included in it, i.e. according to the species richness of plant communities. In different ecosystems, the number of heterotrophic species associated with one plant species increases from several tens to several hundreds. Despite the fact that such "gross" data are very approximate, the principle "diversity breeds diversity" is fundamental for the overall quantitative assessment of the biota of ecosystems.
However, the question of the regularities in the formation of the species richness of plant communities, on the basis of which the composition of heterotrophs (consumers and decomposers) is “estimated”, cannot be unambiguously resolved. R. Whittaker (1980) wrote that species richness is the most difficult to predict characteristic of a plant community.
The main factors that affect the species richness of different plant communities and, accordingly, ecosystems are as follows.
1. "Pool", i.e. the potential stock of species in a given area, the total richness of the flora from which species can be selected to form a particular community.
2. Favorable conditions for the growth of plants that form a phytocenosis (“environmental sieve”).
3. Variability of environmental regimes. With changing environmental conditions (primarily moisture), species richness increases. This explains the very high species richness of the northern steppes (more than 100 plant species per 1 m2).
4. The presence of a violet plant. When it appears, the species richness decreases sharply. An example of this is beech forests, almost devoid of ground cover, and species-poor reed communities in river deltas.
5. Mode of violations. A moderate disturbance regime prevents the strengthening of the role of violets and thus contributes to an increase in species richness (the hypothesis of “high species richness with moderate disturbances”).
6. Carousels (van der Maarel and Sykes, 1993) are small-scale cyclic changes in communities during which several species with similar competitive ability alternately occupy the same ecological niche. “Roundabouts” are most evident in forest communities: when certain tree species fall out, “windows” are formed with their own specific species composition.
7. Time (age of the ecosystem). In order for the community to gather all the species that can potentially grow in it, a certain time is needed. This is a universal factor that operates in any community, but in different "biological time".
All of the above factors in the formation of species richness interact, which explains the complexity of predicting species richness, which R. Whittaker wrote about. He singled out the main geographic latitudinal and altitudinal gradients of species diversity, which increases from high to low latitudes and from high mountains to plains.
IN modern world there is a tendency to reduce the species richness of ecosystems due to the increasing influence of humans on them. Therefore, the existence of many species is threatened.
test questions1. Why is it difficult to obtain data on the complete composition of the biota of different ecosystems?
2. How can you roughly estimate the biological diversity of an ecosystem?
3. What factors influence the biological diversity of plant communities and ecosystems?
10.8. The relationship of biodiversity with the functional parameters of the ecosystem
For the problem of biodiversity protection, the question of its connection with the functional characteristics of ecosystems is important. There is an opinion that the number of species in ecosystems is "redundant", since the number of functional roles is limited and is always greater than the number of their performers. All plants, for example, are phototrophic producers, although they work differently because they have different ecological niches (see 9.2). However, several species can occupy one niche. For example, the disappearance of the scalloped chestnut in American broadleaf forests (see 8.5) has had little effect on the functional parameters of these ecosystems: the chestnut niche has been occupied by other species of broadleaf trees that contribute to primary biological production in the same way as the chestnut. In the floodplains of the European part of Russia, the disappeared elm was replaced by other tree species.
Almost any plant can be consumed by various phytophages, and the diet of most phytophages, in turn, is broad, i.e. they can feed on different species.
All this ultimately gave rise to the opinion of technocratic ecologists (especially American Cornucopians, from cornu-copio - cornucopia) that the number of species is redundant and with the loss of even 1/3 biodiversity there will be no ecological catastrophe.
There is no direct connection between the biodiversity of ecosystems and their productivity (Gilyarov, 1996). In different ecosystems, these relationships are different: there are low-species highly productive ecosystems (reed beds in the deltas of southern rivers) and multi-species low-productive ones (alvar meadows on carbonate soils in Sweden and Estonia).
There is no direct connection between the biodiversity of ecosystems and their sustainability, i.e. the ability to maintain and restore ecological balance under the influence of disturbing factors on the ecosystem. There are stable ecosystems with a small number of species and unstable ones with a large number of species. Thus, on the islands of the Pacific Ocean, prone to frequent hurricanes, the stability of ecosystems is achieved due to a relatively small number of species. At the same time, many biodiversity-rich tropical rainforest ecosystems are proving fragile and slow to recover even after minor disturbances.
All that has been said about the “redundancy” of species that may exist in some ecosystems does not remove the problem of biodiversity protection, since it has a “self-sufficient” value (see 4.6).
test questions1. What is meant by "redundancy" of the species richness of an ecosystem?
2. How are biological diversity and the biological production of an ecosystem related?
3. How are biodiversity and ecosystem resilience related?
1. A variety of views on understanding the scope of an ecosystem.
2. Significance of detritus feeders in the life of an ecosystem.
3. Biological "energetics" of ecosystems.
4. Factors determining biological products and biomass of ecosystems.
5. Why is it important to protect the biological diversity of ecosystems?
Chapter 11
The diversity of ecosystems is very large, and therefore we will consider several examples that are sufficient to illustrate the operation of the two basic laws of life in any ecosystem - the circulation of substances and the one-time use of energy that constantly enters the ecosystem from the outside.
Among natural autotrophic ecosystems, let us consider phototrophic ecosystems of forests and freshwater bodies, seas, as well as chemotrophic ecosystems of "black smokers". We will discuss the features of natural heterotrophic ecosystems using the example of deep-sea "dark" benthic ecosystems in oceans and caves.
Among anthropogenic ecosystems, let us briefly characterize the principles of functioning of agricultural and urban ecosystems. A more detailed consideration of anthropogenic ecosystems is a special task of the sciences of applied ecology - agroecology and urban ecology.
In conclusion, the chapter will consider the system of biomes of the world - the largest units of classification of ecosystems, which are distinguished on the scale of thousands and tens of thousands of square kilometers.
11.1. Phototrophic natural ecosystems: forest and lake
The scheme of “work” of a photoautotrophic ecosystem using sunlight as an energy source and carbon dioxide as a carbon source is well known. Their functional blocks were discussed in Section 10.2. Let us focus on the differences between terrestrial and freshwater ecosystems, which, despite the general scheme of work, differ in many parameters: the nature of limiting factors, the rate of circulation of substances, the length of food chains, the efficiency of energy transfer in these chains, and, finally, the ratio of biological products and biomass (Table . 10).
Table 10 Comparison of the main features of phototrophic freshwater and terrestrial ecosystems
It is obvious from the table that there are three main differences in the functioning of freshwater and terrestrial ecosystems:
– the carbon cycle in the ecosystem of the reservoir proceeds quickly - in just a few months, while in the steppe ecosystem it is 3–5 years, and in forests - tens of years;
- the biomass of producers in the aquatic ecosystem is always less than their biological production for the entire growing season. In terrestrial ecosystems, on the contrary, biomass is greater than production (in the forest - 50 times, in the meadow and in the steppe - 2–5 times);
– the biomass of planktonic animals is greater than the biomass of plants (algae). In terrestrial ecosystems, the biomass of plants is always greater than the biomass of phytophages, and the biomass of phytophages is greater than the biomass of zoophages.
In addition, aquatic ecosystems are more dynamic than terrestrial ones. They change during the day - zooplankton gathers closer to the surface of the reservoir at night, and during the period when the water is translucent by the sun and warms up, it sinks into the depths. The nature of ecosystems changes with the seasons. In the second half of summer, with a high content of nutrients, the lakes “bloom” - microscopic unicellular algae and cyanobacteria massively develop there. By autumn, the biological production of phytoplankton decreases, and macrophytes sink to the bottom.
Ecosystems of lakes change from year to year, depending on the climate and, accordingly, the amount of water that enters the lake in spring and summer (and on its quality, i.e. the content of mineral nutrition elements, organic substances, solid mineral particles, etc.). ). In dry years, the lakes become shallow, the composition of the fish population is depleted in case of kills.
In conclusion, we note that the classes of terrestrial and freshwater ecosystems are internally heterogeneous. In desert ecosystems, the accumulation of detritus is negligible and biological production is low due to water deficiency and high plant respiration costs, while in tundra ecosystems, with relatively low biological production, a large amount of detritus accumulates, since the activity of decomposers and detritivores slows down due to a lack of heat.
Ecosystems of oligotrophic and eutrophic lakes function differently in many respects. In oligotrophic ecosystems, the circulation of substances proceeds mainly in the photic layer, since planktonic consumers simultaneously play the role of decomposers: the phosphorus released by them is immediately absorbed by algae. The intensity of the "nutritional rain" from the photic layer to the darkened near-bottom part is low. In a eutrophic ecosystem, on the contrary, a significant part of phytoplankton is not assimilated by zooplankton, settles to the bottom and serves as food for benthic detritophages. At the same time, excess batteries are buried in sapropel, which causes the process of deeutrophication of the reservoir.
test questions1. List the main differences between terrestrial and freshwater ecosystems.
2. How do the functional parameters of desert and tundra ecosystems differ?
3. What is the main difference between the functioning of ecosystems of oligotrophic and eutrophic lakes?
11.2. Phototrophic ecosystems of the ocean
Ecosystems of the oceans occupy more than 70% of the Earth's area. With the exception of inland seas (large lakes - the Caspian, Azov), these ecosystems communicate with each other. The average depth of the ocean is 3700 m, and life is found throughout the depth, there are no lifeless zones in the ocean. Chemical composition sea water includes 4 main cations (sodium, magnesium, calcium, potassium) and 5 anions (chloride, sulfate, bicarbonate, carbonate, bromide).
In the coastal (it is called the non-retic) zone of the oceans, mineral nutrition elements coming from the land play a certain role. However, in the vast area of the open ocean, ecosystems function only at the expense of carbon and nitrogen, which are assimilated from the atmosphere. The cycles of substances in them are not tied to a specific territory: substances can be carried by sea currents over very long distances.
Currents carry warm and cold masses of water and thus, through its temperature, affect the conditions of life in the ocean. Warm water is carried by the Gulf Stream and the North Atlantic Current, cold water is carried by the California Current (for this reason, fogs are very frequent on the coast of California). In addition to surface wind currents, there are also deep-water movements of water masses. Thanks to the currents in marine ecosystems, there is never a lack of oxygen.
The rise of deep, nutrient-rich waters to the surface of the ocean is called upwelling. It occurs in some places of the World Ocean as a result of a complex interaction of different currents. There are five upwelling regions: Peru-Chile, Oregon-California, Southwest African, Northwest African, Arabian.
In the upwelling zone, as a rule, high biological production is observed, and it is characterized by shortened food chains, with diatoms predominating in phytoplankton, and diatoms predominating in nekton. - herring fish. Fishing is carried out in these areas.
The Peruvian-Chilean upwelling near the western coast of South America (near the Atacama Desert with an average annual rainfall of 10-50 mm and extremely poor vegetation) is associated with the massive development of anchovies, which feed on coastal seabirds - cormorants, pelicans, etc. On the intensity of the formation of secondary biological products in this area can be judged from the following data: 5 million birds annually eat up to 1000 tons of anchovies (in some years the number of birds increases to 27 million individuals). However, such a high consumption of fish by birds does not prevent the annual catch of 10-12 million tons of anchovies, although in some years the catch drops sharply (up to 2 million tons).
Periodic (every few years) increase in the temperature of the surface waters of the Pacific Ocean off the coast of Ecuador and Peru is called El Niño - Southern Oscillation (ENSO). The duration of ENSO is from 6-8 months to 3 years, on average 1-1.5 years. ENSO most often falls on the Christmas holidays (end of December), and therefore the fishermen of the west coast of South America associated it with the name of Jesus in infancy . Each warming of the water sharply reduces the fish productivity of the ocean. Between ENYUK there is a cooling of the water, called by the Peruvians "La Niña" (in translation - a girl).
There are several areas - ocean zones (Fig. 21).
Rice. 21. Zoning scheme of marine ecosystems.
Littoral - coastal zone freed from water at low tide. Under these conditions, flowering plants that are resistant to flooding and salinity grow - sea plantain, triostrennik, sea aster. Zostera and phyllopos-padix settle at the lower border of the littoral and can live permanently in the water. The animal population of the littoral is represented by a large number of specimens of gammarus, littorina mollusks, and mussels.
continental shelf - a zone along the coast to a depth of 200 (rarely 400) m. Underwater thickets of kelp, reaching 16 m in length, are associated with this area. These thickets are inhabited by various crustaceans, mollusks, and nematodes. They eat kelp sea urchins. (In the North Pacific, sea otters feed on sea urchins.) Fishing is associated with this zone. sea fish(herring, cod, flounder, pollock, hake, etc.), crustaceans (crabs, shrimps, lobsters) and mollusks (squid).
Pelagial - the water column of the rest of the ocean. This is the most extensive geographical area of the planet, occupying about 70% of the area of the World Ocean, it is a "desert" with a biomass of 1-2 g/m.
Depending on the depth, four vertical layers of the ocean are distinguished:
– photic – the light part of the ocean, where photosynthetic organisms live (microscopic algae and cyanobacteria, brown and red algae are added to them in the coastal shelf), which form the primary biological product. The thickness of this layer is largely determined by geographic latitude. In the equatorial region, vertically incident sun rays penetrate a water column of 250 m, and in the White Sea the same rays, but incident at an acute angle, can illuminate no more than 25 m. water 10 times;
- aphotic - deeper, a vast "dark" layer of the ocean, which is home to a variety of heterotrophs, including many fish;
- abyssal(benthal) - the near-bottom region of the aphotic layer of the pelagial (“eternal night”), where protozoa from the order of foraminifers are common (up to 0.5 million copies per 1 m 2) and nematodes - very small roundworms (0.5-1 mm length). Of the large organisms, sea urchins, sea cucumbers, sea lilies and sponges are found, but not more than one specimen per 1 m.
– ultrabyssal – deep-sea trenches at a depth of more than 8 thousand m, where a column of water weighing more than 1 ton presses for every 1 cm 2 of the surface. However, there is life in this part of the ocean - holothurians, starfish, bivalve mollusks, various crustaceans live.
Food chains in oceanic ecosystems, as in freshwater, usually consist of 6 links, the last link is represented by nekton - fish, mammals and mollusks. About 10% of biological products in the "nutrient rain" fall into the dark depths of the ocean, including only 0.03-0.05% buried in sediments, the rest is consumed by heterotrophs. Production increases with sea waves, which contribute to the enrichment of water with oxygen.
Coral reefs, estuaries (estuaries, coastal areas where rivers flow) and upwelling zones have the highest biological production. The zone of the continental shelf is moderately productive.
test questions1. Tell us about the "horizontal" zoning of the ocean.
2. What "vertical" zones are different in the ocean?
3. How many links make up the food chains of ecosystems in the photic layer of the ocean.
4. What role do currents play in the life of ocean ecosystems?
5. List the main upwelling areas.
11.3. Chemoautotrophic ecosystems of rift zones
In rift zones (places of faults in the lithosphere plates) of the underwater ridge of the Pacific Ocean, hot waters saturated with hydrogen sulfide, sulfides of iron, zinc, copper and other heavy metals are emitted from rock crevices. In these areas in the 70s. In the 20th century, chemoautotrophic ecosystems were discovered, which were called deep-sea geothermal "oases". The temperature of the "geysers" reaches 300°C, but the hot waters do not boil due to high pressure. The salts contained in hot water, upon contact with cold sea water, precipitate and form cone-shaped formations up to 15 m high, which are called "black smokers". At the bases of "black smokers" an "oasis" is formed.
The producers of these ecosystems are sulfur bacteria that form clusters - bacterial mats. Due to symbiosis with them, the most important organisms of this ecosystem also live - vestimentifera - representatives of the pogonophora type (worms 1–2.2 m long, enclosed in long white tubes of a chitin-like substance, see 8.6). In these ecosystems, in addition, there are many species of predatory animals (crabs, mollusks, some deep-sea fish).
Later, similar "oases" were discovered in other oceans. The biological production of "oases" exceeds the production of typical benthic heterotrophic ecosystems by tens of thousands of times (see 11.2). The biomass of vestimentifer alone can reach 10–15 kg/m.
However, the ecosystems of "oases" do not exist for long and are destroyed after the activity of underwater geysers ceases.
In addition to the "oases", there are also geothermal "fields", which are found along the Central Atlantic Ridge, stretching from Iceland to the equator. They cover directly the ridge and the raised areas of the bottom surrounding it, the width of the "fields" can reach 75 km. The temperature of the waters rising from the crevices is from 50 to 300°C. The life of ecosystems of "fields", unlike "oases", is represented only by bacteria. The composition of bacteria and the productivity of these ecosystems have not yet been studied, but it is obvious that it is much higher than that of typical abyssal ecosystems.
To date, more than 40 "fields" have been explored, and especially carefully - the "Lost City", located 15 km from the main ridge of the Central Atlantic Ridge (30 o N) at a depth of 700-800 m. irregularly shaped formations resemble fairy-tale castles 60-80 m high.
test questions1. What are the conditions in the deep ocean rift zones?
2. Tell us about the ecosystems of "black smokers".
3. What are geothermal fields and where are they common?
11.4. Heterotrophic and autotrophic-heterotrophic natural ecosystems
Heterotrophic ecosystems exist due to the input of organic matter from outside, i.e. dependent on autotrophic ecosystems. Such relationships can be considered as “commensalism at the ecosystem level”: ecosystems supplying organic matter do not suffer significantly from these supplies, while heterotrophic ecosystems receiving organic matter benefit.
Ecosystems of deep oceans are heterotrophic, in which organisms live on a meager "nutritional rain" from the remains of plankton and nekton organisms and pellets - excrement of crustaceans packed in special shells. Organic matter falling out of the light layer of the ocean is gradually eaten up as it sinks into the deeper layers, and mere crumbs get to a depth of 4-5 km, where some mollusks, crustaceans and even fish live in pitch darkness. As a result, the biological production of such ecosystems is extremely low, and the biomass reserve is fractions of a gram per 1 m3.
Even lower is the biological production and biomass of tick communities on eternal snows, which live on organic residues blown from below from populated vertical mountain belts.
Dark cave ecosystems are typically heterotrophic. The entry of organic matter into them is associated either with the excrement of bats, which fly out of caves at night to hunt, or with organic matter, which is brought into the cave by the current of water from illuminated areas (Birshtein, 1985). The population of such ecosystems may include beetles, arachnids, wood lice and centipedes. The second trophic level (predators) in cave ecosystems, as a rule, is not expressed, but decomposers are abundant.
There are transitional types of ecosystems from autotrophic to heterotrophic, such as shaded forest water bodies, where the main source of organic matter is tree leaf litter, but there are also some autotrophic plankton organisms. Y. Odum (1996) describes an autotrophic-heterotrophic mangrove ecosystem in estuaries, where the main food chain is detrital, which is opened by numerous detritivores feeding on falling leaves. In addition to detritus feeders, such ecosystems contain at least two trophic levels of predatory fish.
test questions1. Describe the benthic ecosystems of the deep ocean.
2. Due to what sources of matter and energy do dark cave ecosystems function?
3. Give examples of natural autotrophic and heterotrophic ecosystems.
11.5. agricultural ecosystems
Agricultural ecosystems (agro-ecosystems) occupy about 1/3 of the land area, while 10% is arable land, and the rest is natural fodder land. Agroecosystems are photoautotrophic - they have the same basic scheme of functioning with the transfer of energy along the chain "producers - consumers - decomposers" as natural terrestrial ecosystems. Their difference lies in the fact that the composition, structure and function are controlled not by natural mechanisms of self-organization, but by a person. As Y. Odum (1986) writes, a person stands at the top of the ecological pyramid and strives to straighten food chains in such a way as to obtain the maximum amount of primary (crop) and secondary (livestock) products of the required quality (Odum, 1986).
In addition, agroecosystems are much more open than natural ecosystems: with crop and livestock products, nutrients are outflow from them. A certain amount of nutrients is also lost due to leaching into ground and surface waters, as well as erosion - washing away or blowing off fine earth from the fields, which is the most nutritious part of the soil.
Rice. 22. Agricultural ecosystem management scheme (according to Mirkin, Khaziakhmetov, 2000).
In order to manage the agroecosystem (Fig. 22), a person spends anthropogenic energy - on tillage and irrigation, on the production and application of fertilizers and chemical plant protection products, on heating livestock buildings in winter, etc. The amount of anthropogenic energy expended depends on the chosen management strategy. Agriculture can be intensive (high energy input), extensive (low energy input) or trade-off (moderate energy input). A compromise strategy is the most appropriate, as it allows you to combine a sufficiently high yield of agricultural products with the preservation of environmental conditions and energy savings.
However, even with an intensive management strategy, the share of anthropogenic energy in the energy budget of the ecosystem is no more than 1%. The main source of energy for the "work" of the agroecosystem is the Sun.
Man controls almost all parameters of the agroecosystem:
- the composition of producers (replaces natural plant communities with artificial sowing of agricultural plants and planting fruit trees);
- the composition of consumers (replaces natural phytophages with livestock);
- the ratio of energy flows along the main food chains "plant - man" and "plant - livestock - man" (specializes the economy in the production of crop or livestock products or an equal ratio of both);
- the level of primary biological production (improving conditions for plant development through tillage, fertilizers and irrigation).
Man manages the agroecosystem through biological intermediaries, which include cultivated plants, farm animals, soil biota and all other organisms inhabiting the agroecosystem (entomophage insects and pollinators, birds, hayfields and pastures, etc.). Intermediaries play the role of biological amplifiers that allow reducing the cost of anthropogenic energy.
Methods for managing the agroecosystem have been improved over ten thousand years of the history of agriculture (powerful agricultural machinery, mineral fertilizers, pesticides, growth stimulants, etc. have appeared), but management options are still limited today by a number of environmental and biological conditions:
- agro-resources - climate (precipitation and duration of the warm period), the nature of soils and topography. The composition of species and varieties of cultivated plants and species and breeds of agricultural animals depends on these conditions;
- the potential for the formation of primary biological products - the upper limit of the efficiency of photosynthesis, which in most cases does not exceed 1% of the incoming solar energy (in especially productive crops in a warm climate on fertilizer and irrigation - up to 2%);
- the maximum possible share of economically valuable fractions in the crop - cotton fiber, tubers, root crops, grain, etc. (for example, grain can be no more than 40% of all biological products, although the wheat of the Mexicane variety, bred by the “father” of the green revolution N. Berloug, managed to bring the share of grain to 60%);
– the inevitable dissipation of energy during its transition from the first trophic level to the second (when fattening livestock): to obtain 1 kg of secondary biological products when fattening broilers, pigs and cows, it is necessary to spend (in terms of grain) 2, 4 and 6 kg of feed;
- the fertility of farm animals: the upper limits of egg production of chickens, the number of offspring in cows and pigs, etc. are limited.
Biological constraints cannot be overcome, although the impact of resource constraints can be weakened with an intensive management strategy (high doses of fertilizers, irrigation, creation of protected ground, terracing of slopes). However, as the experience of the green revolution of the 60s showed. In the 20th century, when super-yielding varieties came to the fields, high energy investments led to the destruction of agricultural resources - soil, depletion of water resources and its pollution, and a decrease in biodiversity. Thus, high energy costs for the management of the agroecosystem are ecologically unjustified. In addition, energy itself is scarce, as energy resources are limited, and the production and transportation of energy are accompanied by environmental pollution.
For this reason, with an environmentally oriented management of the agroecosystem and moderate costs of anthropogenic energy, obtaining a sufficiently large amount of high quality agricultural products does not reduce the stability of the agroecosystem (i.e., ensures the conservation of its agricultural resources).
In order to farm in accordance with these requirements, a person is forced to limit:
- the share of arable land (especially under profitable but soil-destroying crops - sunflower, corn, rice), while maintaining part of the agroecosystem under perennial grass communities of fodder lands or under forest (natural or forest plantations);
- intervention in the life of the soil during its cultivation (use not dump plows, but rippers) and doses of mineral fertilizers and chemical plant protection products;
- number of livestock.
In addition, for the environmentally oriented management of agro-ecosystems, it must:
– cultivate species and varieties of cultivated plants and breed farm animals that require less anthropogenic energy (drought-resistant species that do not require irrigation, such as sorghum; horses that are kept on pastures all year round, etc.);
- use eco-friendly crop rotations with perennial grasses and green manure (their green mass is not harvested, but plowed into the soil as a fertilizer) to restore soil fertility;
– to cultivate polycultures and variety mixtures, i.e. mixtures of cultivated plants that use agricultural resources more fully and require less plant protection costs;
– disperse livestock throughout the agroecosystem (keep them on small farms) to facilitate the application of manure to the fields.
Agro-ecosystems that are created in accordance with these principles are called self-sustaining (sustainable). They provide the maximum possible similarity with natural ecosystems.
Unfortunately, at present the share of sustainable agro-ecosystems in the world (and especially in Russia) is small. Under the influence of agriculture, the destruction of soils continues, the hydrological and hydrochemical characteristics of agricultural landscapes are disturbed, and biological diversity is declining.
test questions1. What land area of the planet is occupied by agroecosystems?
2. How do agroecosystems differ from natural photoautotrophic ecosystems?
3. What is the share of anthropogenic energy spent on the management of the agroecosystem in the energy budget of the latter?
4. List the main parameters of the agroecosystem that are controlled by humans.
5. What biological mediators do humans use to manage an agroecosystem?
6. List the resource constraints in the management of the agroecosystem.
7. Tell us about biological constraints in agroecosystem management.
8. What is a compromise agroecosystem management system, what are its environmental and economic benefits?
9. What parameters characterize a sustainable agroecosystem?
11.6. urban ecosystems
Urban ecosystems (territories of cities and their population) are heterotrophic anthropogenic ecosystems. However, unlike agricultural ecosystems, they do not have elements of self-regulation. Attributing cities to ecosystems is rather conditional; rather, they are “anti-ecosystems”, which are characterized by three features:
- dependence, i.e. the need for a constant supply of resources and energy;
– disequilibrium, i.e. the impossibility of achieving ecological balance;
– accumulation of solid matter due to the excess of its import into the city over export (approximately 10:1). In the past, this led to an increase in the surface level of the city (the formation of a cultural layer, which in old cities reaches several meters), and today it leads to an increase in the area of landfills for storing domestic and industrial waste.
The tasks of environmentally oriented management of urban ecosystems, in contrast to the management of agroecosystems, which is carried out using intermediary organisms, are purely technological, related to the improvement of production technologies for industrial enterprises, the greening of public utilities and transport.
By improving production and vehicles and developing the public urban transport system (the latter is especially important, since cars contribute from 50 to 90% of urban air pollution), the quality of the urban atmosphere and water is improving.
Technologically, the problems of reducing the energy consumption of cities are also solved by dispersing installations for generating energy (from carbon energy carriers, solar collectors, etc.), its more economical use in public utilities (replacing incandescent lamps with cold glow lamps, thermal insulation of walls, the use of economical household appliances etc.) and industrial enterprises. Similarly, engineering issues are water consumption and, accordingly, the treatment of polluted effluents, reducing the amount, storage and processing of municipal solid waste.
Each citizen works from 1 to 3 hectares of agricultural land (including 0.5 hectares of arable land). Accordingly, the ecological task is the economical use of food products and the prevention of their spoilage.
If a person cannot make the urban environment balanced, then he must do everything possible to limit the detrimental impact of cities on the natural and agricultural ecosystems that surround them.
Cities must remain within their established boundaries and grow upwards first, making room for green spaces, which are the most effective and versatile means of improving the urban environment. Green spaces improve the microclimate, reduce chemical pollution of the atmosphere, reduce the level of physical pollution (primarily noise) and have a beneficial effect on the psychological state of citizens. According to environmental standards, one citizen should have 50 m 2 of green space within the city and 300 m 2 in suburban forests.
test questions1. List the main features of urban ecosystems.
3. What is ecocity?
4. In what direction should modern cities be greened?
11.7. Biomes
Biome - it is the highest unit of ecosystem classification. According to Y. Odum (1986), this is a large regional or subcontinental biosystem characterized by some basic type of vegetation or other landscape feature. The biomes of terrestrial ecosystems are formed under the influence of a complex of environmental conditions, primarily climate. In terms of volume, "biome" coincides with the geographical concept of "natural zone".
The most important land biomes:
- tundra (arctic and alpine) - treeless territories located to the north (or above) of the forest belt;
- taiga - coniferous forests of the temperate zone;
- deciduous (broad-leaved) forests of the temperate zone;
- steppes of the temperate zone (they have two pauses in the growing season - in winter and in the second half of summer during a drought);
- tropical steppes and savannahs (vegetate all year round, but during the drought period their biological production drops sharply);
- deserts – ecosystems under severe drought stress with annual precipitation less than 200 mm;
- semi-evergreen seasonal rainforests ("winter-green" forests that shed their leaves in summer);
- tropical rainforests (vegetate all year round and are the most productive ecosystems on Earth).
The biomes of aquatic ecosystems are determined primarily by the salinity of the water, the content of nutrients in it, oxygen and temperature, and the speed of the current.
Thus, freshwater ecosystems are divided into stagnant and flowing water biomes. Ecosystems of stagnant waters are more diverse, since in this case the limits of changes in the conditions that determine the composition of biota and its products are wider - the depth of the reservoir, the chemical composition of water, the degree of overgrowth of the reservoir. In the biomes of flowing waters, the flow velocity plays an important role, and the composition of the biota on rifts and reaches is different.
Among the ecosystems of sea coasts, there are biomes of seaside rocky coasts, which are rather poor in nutrients, and estuaries (estuaries) - mudflats rich in nutrients at the confluence of rivers.
Among the pelagic ecosystems of the ocean, biomes of photic (autotrophic) communities of the upper layer of waters (surface pelagic communities) and marine deep-sea pelagic heterotrophic communities are distinguished.
As biomes, benthic communities of the continental shelf, coral reefs (highly productive communities of tropical seas), and chemoautotrophic communities of hydrothermal oases are considered.
Biological production and biomass of ecosystems of different biomes differ significantly (Table 11).
Table 11 Biological production and biomass of the world's major biomes (in dry matter, Whittaker, 1980)
test questions
1. What is a biome?
2. List the main land biomes.
3. What biomes stand out in the oceans?
4. By what principle are biomes of continental water bodies separated?
Topics of reports at seminars1. Diversity of terrestrial ecosystems.
2. Diversity of freshwater ecosystems.
3. Ecosystems of the oceans.
4. Features of agricultural ecosystems.
5. Environmental problems urban ecosystems.
Chapter 12 Ecosystem Dynamics
Ecosystems are constantly changing, and in different "biological time" and different "biological space". At the same time, at any point in the ecosystem, under the influence of a variety of causes, changes occur simultaneously, overlapping each other. The situation is reminiscent of the trajectory of a molecule in a flask of a laboratory stirrer, in which a mixture of soil and water is stirred up. The molecule performs Brownian motion, together with the flask - oscillatory, "shaking" in the stirrer, moves along with the planet when it rotates around its axis and flies around the sun, traveling in the galaxy along with solar system, etc. In addition, this complex trend of changing the position of a molecule can include its movements due to the rise and fall of the land level, local fluctuations in the soil surface due to the passage of heavy equipment, etc.
For this reason, in order to understand the general patterns of ecosystem dynamics, it is necessary to dissect all the components of changes under the influence of various factors and consider them separately in different "biological space" and in different "biological time".
One important preliminary remark should be made. We have already noted that it is not possible to completely recalculate all the species that make up the ecosystem with real time costs. That is why ecologists understand ecosystems as primarily functional phenomena, evaluate their productivity, cycles of substances, patterns of energy transfer along food chains, etc. For the same reason, no one has ever tried to study the dynamics of ecosystems, taking into account all the species that make up them. Most often, the dynamics of terrestrial ecosystems is judged by the change in the state of its autotrophic block - the totality of plant communities (or one plant community), a priori believing that these changes also induce the restructuring of the entire heterotrophic biota of the ecosystem in accordance with the principle "diversity generates diversity". In this case, the connection of heterotrophic biota with plants can be direct - they feed on these plants and indirect - the composition of the plant community reflects the state of environmental conditions that affect the composition of consumers and decomposers (soil moisture, oxygen content in water, environmental reaction, etc.) .
The dynamics of ecosystems is usually studied according to the scheme:
a) identification of the dynamics of plant communities with the allocation of stages of this dynamics as a kind of "outline" for studying changes in the heterotrophic components of the ecosystem;
b) study of the dynamics of heterotrophic biota. At the same time, the dynamics of either the most important species (rare or resource species for the purpose of their protection or rational use) or large taxonomic groups - birds, fish, mammals, individual groups of insects - is studied.
The dynamics of plant communities is one of the most developed sections modern science about vegetation (Mirkin et al., 2000). That is why, considering the dynamics of ecosystems, we will largely rely on the theoretical developments of this science.
12.1. Classification of ecosystem changes
All changes can be divided into two large classes, however, also connected by a smooth transition: cyclical dynamics and vectorized (directed) changes.
Cyclical changes - these are changes in the composition, structure and functions of the ecosystem around a certain average value corresponding to the state of ecological balance. With ecological balance in an ecosystem:
- the composition of species remains constant (although some of them are periodically dormant or absent as a result of migration);
- the production of autotrophs is completely processed by heterotrophs (the total production of the biocenosis is equal to its total respiration), although some of it may temporarily turn into detritus;
- the cycles of substances are closed: how much of an element is consumed by organisms, so much is returned back to the environment.
If a certain amount of substances left the ecosystem (due to “background” soil erosion, subsoil runoff, due to denitrification, evaporation, etc.), then it is compensated by the influx of substances into the ecosystem from outside (the process of leaching of parent rocks, biological nitrogen fixation, precipitation falls, etc.).
Directed(vectorized) changes - these are changes in the composition and functional parameters of the ecosystem. By their nature, they can be divided into three main types.
Violations - abrupt changes in the composition and function of the ecosystem under the influence of an external factor - during an earthquake, mudflow, fire, flood, plowing, deforestation, oil spill, etc. Different disturbances cover different biological spaces: from a few square meters (spill of a small amount of oil, cutting down of one or several trees) to tens of square kilometers (large fires).
Depending on the factor that caused the violation, and the characteristics (stability) of the ecosystem, the result may be different. So different that it is difficult to make any generalizations about the response of ecosystems to disturbances.
Autogenous successions - gradual changes in the ecosystem under the influence of the vital activity of its biota, in which the composition of species and the functional parameters of the ecosystem change in the direction of the formation of a steady state in equilibrium with the climate - the climax. Depending on whether biological production, biomass stock, species richness increase or decrease during successions, they are divided into progressive And regressive.
There are three variants of autogenous successions:
– primary autotrophic. These successions start from zero, i.e. in conditions where there was practically no life, which, in the course of succession, develops a new space;
– secondary autotrophic(recovery). These successions begin after the complete or partial destruction of the ecosystem under the influence of disturbances or after the termination of the process of allogeneic successions discussed below. As a rule, secondary successions proceed faster than primary ones, since some reserve of “life remains” remains from the destroyed primary ecosystem - plant seeds and their vegetative organs in the soil, moss and fungal spores, resting stages of soil animals, etc. ;
Allogeneic succession - changes in ecosystems under the influence of an external factor in relation to them. These successions continue as long as an external factor is in effect. As soon as its action ceases, secondary restorative succession will begin.
The evolution of ecosystems. These changes are also gradual, like successions, but differ in the result - new ensembles of species arise, which have not yet been in nature. Such changes in ecosystems can be natural and anthropogenic. Natural evolution takes place on a geological time scale. She's almost completely overwhelmed at the moment. anthropogenic evolution ecosystems.
Like successions, the evolution of ecosystems can be not only progressive accompanied by their complication (enrichment of species composition), but also regressive at which the biota composition of the ecosystem is depleted. Regressive, as a rule, is the anthropogenic evolution of ecosystems.
Let us consider the listed variants of ecosystem dynamics in more detail.
test questions1. What are the common features of cyclic changes in ecosystems?
2. List the main forms of directed changes in ecosystems.
3. What is the difference between progressive and regressive changes in ecosystems?
12.2. Cyclical changes in ecosystems
Cyclic changes in ecosystems are very diverse, they can be caused by abiogenic causes (first of all, changes in conditions in the daily, annual and multi-year (multi-annual)) and biogenic - fluctuations in the density of populations of "key" species. Cyclic dynamics proceeds on different scales of "biological time" and "biological space".
Diurnal Changes are most evident in aquatic ecosystems, where during the period of maximum illumination, zooplankton disperses throughout the water column, but in the evening, when illumination decreases, it concentrates near the surface. Diurnal changes are associated with biorhythms (see 4.4.2): in the life of diurnal and nocturnal animals, in the closing of flowers at night, in the change in the position of the leaf blades of many tree species. In the nut-bearing lotus, which forms “fields” in the Astrakhan Reserve, at night the leaves lie on the surface of the water, like a water lily or a water lily, but during the day they rise several centimeters above it, which dramatically changes the living conditions of the population of the surface of the reservoir, which can live in the daytime under a lotus leaf umbrella.
In the daily rhythm, the functional parameters of the ecosystem also change - the intensity of photosynthesis and the processing of primary biological products into secondary ones. Only in the soil inhabited by an armada of protozoa and invertebrates does life slow down slightly at night.
Seasonal changes. The seasonal rhythms of organisms are well known. The life cycles of most living organisms are associated with the seasons of the year (flowering and fruiting of plants, breeding by animals, etc.). The inhabitants of the ecosystem are well adapted to the change of seasons: plants shed their leaves for the winter, warm-blooded animals "warm up", increasing the layer of fat and the density of their coat, hibernate or migrate to more favorable conditions (birds), change "camouflage robes" (hares become white), etc. Depending on the season of the year, the functional parameters of the ecosystem also differ significantly. In temperate latitudes in winter, production and respiration are sharply reduced, although in tropical forests the seasonality of the "work" of the ecosystem is practically absent. In the steppes, the life of ecosystems slows down twice - in winter and in the second half of summer during the period of moisture deficiency.
Seasonal dynamics is clearly manifested in aquatic ecosystems. In the first half of summer, the water is saturated with mineral nutrients and phytoplankton species multiply rapidly (according to the exponential curve). Their abundance decreases by the middle of summer as a result of grazing by zooplankton. By autumn, macrophytes sink to the bottom. Eutrophicated reservoirs “bloom” in the second half of summer (mass development of cyanobacteria occurs).
Long-term (multi-annual) changes. They are even more varied. Under the influence of climatic features of the year (temperature dynamics, precipitation, floods in floodplain ecosystems), the value of primary and secondary biological production changes. In addition, some species survive climatically unfavorable years in a dormant state (in a year of drought, no more than one third of plant species develop in meadow communities, and the rest pass into a state of dormancy - seeds, “sleeping” underground organs, etc.). Changes in the composition of the animal population can be no less significant. This is how locust migrations are generated by droughts.
An example of long-term changes in ecosystems caused by biotic causes is the dynamics of the steppe ecosystems of Mongolia under the influence of outbreaks of Brandt's vole, a mouse-like rodent, which is a "key" species. With the mass development of voles, the composition of the plant community changes dramatically: instead of feather grasses, the leaves of which are eaten by rodents, shoots of other grasses develop from underground rhizomes, especially raptor (Elymus chinensis). However, after the peak of abundance, a decrease in the density of the rodent population begins. And after a few years, feather grass populations are also restored, and rhizomatous grasses go into their former state of “semi-rest” and “prepare” for a new outbreak of rodent abundance. Phase fluctuations "Elymus chinensis - Stipa krilovii" - salient feature Mongolian steppes, which was described by prominent researchers A.A. Yunatov and E.M. Lavrenko.
In European broad-leaved forests in some years, the gypsy moth develops massively. Its caterpillars almost completely eat the foliage of trees, which improves the conditions for the life of ground cover plants (illumination, provision with mineral nutrients due to caterpillar excrement). As a result, the biological production of trees drops sharply, but the production of herbs and, accordingly, the phytophages associated with them, increases.
Wild boars constantly search through forest areas in search of food. On pores with an area of several tens of meters, ruderal plants grow, however, within 4-5 years, the ground cover is restored and, as a result, the cyclic dynamics of the entire biota. Naturally, the “plowing” of a forest area by wild boars dramatically changes the life of the entire soil cenosis. The activity of aerobic bacteria and animals that prefer the conditions of loose and well-aerated soils is activated.
The cycles caused by the activity of beavers are longer: after they dam the river, an intensive restructuring of the ecosystem takes place over the course of several years and the role of moisture-loving plants and their companions increases. Tree species that are resistant to flooding and flooding generally die. However, for 10-20 years of using this territory, beavers eat away the plants that serve as a food base for them (primarily alder) and change their place of residence. There is a rather rapid destruction of the “hydromeliorated” ecosystem and the restoration of the former one. This cycle continues for about 100 years.
On a scale of decades, there are reversible changes in the forests of the Far East associated with the biological cycles of bamboo species from the genus Sasa, which are key in these ecosystems. Bamboos growing in the undergrowth inhibit tree regeneration. But they are monocrabs (that is, they bear fruit only once and then die), and after the death of the next generation of bamboo, tree populations are actively renewed for several years until its next growth.
In the broad-leaved forests of Eastern Europe, as a result of the loss of individual trees (from old age or under the influence of the wind), "windows" are formed. In “windows” several tens of meters in size, communities of explerents (ruderal grasses, alder, birch) are formed, which after several decades are replaced by the “main” species of this type of forest. Rainforest researchers have called these successive groups "dryads" and "nomads". The dynamics of "dryads" and "nomads" corresponds to one of the models of ecosystem stability: stability on a large scale of biological space is made up of instabilities on its small scale.
In general, any cyclic changes in ecosystems are a reflection of their plasticity, i.e. adaptability of composition, structure and function to fluctuations in environmental conditions and life cycles of "key" species.
test questions1. List options for cyclic changes in ecosystems.
2. Give examples of daily changes in ecosystems.
3. Give examples of seasonal changes in ecosystems.
4. For what reasons do year-to-year changes in ecosystems occur, give examples of them.
12.3. Primary autogenous successions and climax
Primary autogenous successions of overgrowing of substrates formed after the melting of the glacier on Novaya Zemlya were described by the Russian scientist K. Baer at the beginning of the 19th century (Trass, 1976). Nevertheless, the concept of primary autogenous succession, as a result of which the ecosystem passes into an ecologically balanced state, most appropriate to the climate, is associated with the name of the outstanding American ecologist F. Clements. This equilibrium state was called menopause. Ecosystems of stages of succession on the way to climax Clements called serial.
Clements believed that in any geographic area with one type of climate, there is only one type of ecosystem (monoclimax) that is most suited to that climate. For example, in Eastern Europe in the taiga biome it is a spruce forest, in the broad-leaved forest biome it is a linden-oak forest, in the steppe biome it is a forb-feather grass steppe. All other types of ecosystems "tend" to move into this type, i.e. there is a process of convergence (levelling) of the composition of ecosystems of one region: soils are formed on the rocks; lakes overgrow, turning into swamps, which dry up over time; there is a grinding of mineral particles (sands turn into loams); drier habitats become wetter due to the accumulation of organic matter, which is able to retain rain and snow water.
In addition, Clements singled out many different types of communities (and their corresponding ecosystems), which, as a result of the action of some external factor, “get stuck” at a certain stage of succession and cannot pass into climax, i.e. are chronically serial. For example, a subclimax is a river floodplain ecosystem that does not transition to a climax due to regular floods. Disklimax is an ecosystem that does not go into climax as a result of the action of a factor that violates it (for example, intensively used pasture).
During the succession of ecosystems that form the climax, productivity and biomass, species richness, and structural complexity increase (soils are formed, plants of different life forms appear - trees, shrubs, grasses, which forms additional niches for heterotrophs). The role of various mechanisms of coexistence is increasing - differentiation of ecological niches, mutualism, co-adaptation between predators and their prey, etc. The conditions for the life of plants and species of heterotrophic biota improve during such succession, and the sequence of species in the course of succession is strictly determined by the laws of "ontogenesis" of ecosystems.
Ecologists who developed a functional view of the ecosystem (A. Lotka, G. Odum, R. Pinkerton, R. Margalef) emphasized that as we approach the climax, the energy flow shifts from productivity to respiration (Lotka even spoke of the “law of maximum biological energy "). Yu. Odum (1986) emphasized that in the course of succession, as it approaches the climax, the ratio of production (P) and respiration (R) is equalized, i.e. in the climax ecosystem Р=R. All production that is formed during the year is spent on respiration, and therefore there is no further increase in biomass. The ratio of biomass to production (B/P) increases until there is a maximum of biomass per unit of energy flow for a given climate (this maximum will differ in the zones of taiga, deciduous forests, steppes, deserts, etc.).
As we approach the climax, the cycles of nutrients become more and more closed and slow, and the proportion of nutrients that are fixed in living organisms and detritus (including soil humus) increases.
In the course of succession, “relay races” of representatives of flora, fauna, fungi, microorganisms occur, and in most cases, types of r-strategy are replaced by types of K-strategy (according to MacArthur and Wilson) or (according to Ramensky and Grime) types of strategy R - types of strategies C, S and various transitional secondary types (CS, CR, RS, CRS). Thus, juveniles are replaced by perennials, and grasses by trees, which leads to an increase in biological production due to a more complete use of resources.
Clements' work will forever remain a classic of ecology and a cornerstone of the theory of ecosystem dynamics. Nevertheless, the ideas formulated by him in the course of the further development of ecology have undergone significant changes:
1. A. Tansley and A. Nicholson have shown that in one region, not one, but several climaxes can form, i.e. ecosystems that are formed during successions of overgrowth of rocks, lakes, sands, loess-like loams, etc., will be different. The concept of monoclimax thus developed into the concept polyclimax. R. Whittaker, developing these ideas, formulated the concept of "climax-continuum". He believed that different polyclimax ecosystems are connected with each other by smooth transitions, and for this reason, each point has its own climax.
2. Menopause is not necessarily the most productive and rich in species ecosystem. As a rule, “pre-climax” serial ecosystems are distinguished by the highest species richness and productivity.
3. Succession is not a rigidly determined, "programmed" process, similar to the ontogeny of an organism, but has a stochastic character. Regularities of successions can be revealed only by generalizing (averaging) the results of observations of several specific successions occurring under the same conditions. In specific successional sequences, the arrival of species into succession and departure from it can occur in different order. Moreover, some species may participate in one particular succession and not participate in another. We have already said that functional "roles" in any ecosystem are always much smaller than the number of their possible "performers" (see 10.8).
test questions1. Tell us about the ideas of F. Clements on the issue of ecosystem dynamics.
2. List the functional parameters of the climax ecosystem.
3. Species with what types of strategies are presented at different stages of autogenous succession?
4. What provisions of F. Clements' concept of ecological succession and climax have been revised?
12.4. Autogenous succession models
F. Clements believed that all successions in the development of ecosystems in the direction of climax obey one model: conditions for the life of biota improve, and therefore the biological production and species richness of the ecosystem increase. Modern ecologists distinguish at least three models of successions (Connell and Slayter, 1977):
- favored model. Corresponds to the concept of Clements' succession: productivity and species richness increase during succession up to the climax stage. A classic example of such a succession is the overgrowth of rocks, where the stages of cyanobacteria and algae, scale lichens, fruticose lichens and mosses, grasses, shrubs and trees successively replace each other;
- model of tolerance. In the course of succession, conditions worsen, for example, the transition of a lowland bog to a raised bog, during which the conditions for mineral nutrition deteriorate, and therefore productivity and species richness decrease. The conditions for the life of the biota also worsen during succession on rich substrates: the first settler plants get more resources of mineral nutrition and light than the second and third, which must provide themselves with resources in the face of increasing competition;
is the inhibition model. In the course of succession, a "key" species (or guild of key species) appears that blocks further changes. As a result, succession stops and it does not reach the climax stage. For example, on forest fires in Scotland, cuckoo flax blocks the settlement of trees, in the deserts of Central Asia, the settlement of shrubs and saxaul is prevented by the crust, which is formed by cyanobacteria, algae and some mosses. Prairie restoration North America is blocked by the growth of alien European annual grasses, primarily Bromus tectorum.
In the course of succession, the favored model may be replaced by the model of tolerance: at the first stages, conditions improve, and as they approach the climax, they worsen.
An illustrative example of succession with a change in pattern is the formation of vegetation during the release of the coast of the fiord from ice in Alaska (Chapin et al., 1994). There are four stages of the process:
– pioneer (up to 20 years). The surface of the substrate is covered with a "black crust" of nitrogen-fixing cyanobacteria, horsetail gametophytes (Equisetum variegatum), lichens, liverworts, against which there are scattered grasses, Dryas drummondii shrub, individual specimens of willow, poplar (Populus trichocarpa), spruce (Picea sitchensis) and alder (Alnus sinuata);
- Dryas stage (between 20 and 30 years). The entire surface is covered with a carpet of shrubs, in which single specimens of willows, poplars, firs and alders are scattered;
- alder stage (between 50 and 100 years);
- spruce stage (after 100 years).
In the course of succession, soil is formed, which is enriched with organic matter and nitrogen, and the change of plant species goes towards increasing their height and life expectancy, which corresponds to the favorable model. However, at the same time, the level of competition for light and soil resources increases (especially at the spruce stage), the conditions for survival of seedlings deteriorate, and the probability of seed death increases, which corresponds to the tolerance model. change of models occurs at the fourth stage.
The replacement of the model of favored environment with the model of tolerance is also characteristic of the succession of ecosystems in warm climates. Thus, during the overgrowth of lava flows, at the first stages, the conditions are improved due to legumes (especially from the Lupinus r.), which contribute to the enrichment of the substrate with nitrogen, and later they worsen, as competition intensifies.
Despite the fact that autogenous successions proceed spontaneously according to their inherent internal laws, a person, knowing these laws, can influence the rate of succession. So, to accelerate the self-overgrowing of waste rock dumps, their surface is covered with a thin layer of peat or soil, which contains plant seeds. In addition, the overgrowing process can be accelerated by sowing meadow grass seeds or planting shrubs and trees.
test questions1. What is the difference between successions proceeding in accordance with the models of favor and tolerance?
2. Give examples of successions proceeding according to the inhibition model.
3. Give examples of successions with changing models.
12.5. Heterotrophic successions
The driving force behind autotrophic successions is solar energy, which is assimilated by producer plants and transferred through food chains to consumers and decomposers. However, just as there are heterotrophic ecosystems, heterotrophic successions are also possible (they are also called degradation ones). These successions occur during the decomposition of dead organic matter (detritus): an animal carcass, cow dung "cakes", a fallen tree trunk, forest floor, etc. In heterotrophic successions, there is a "relay race" of biota, which is represented by invertebrates, fungi and bacteria.
Heterotrophic succession in fallen pine needles lasts about 10 years (Bigon et al., 1989). Since the fallen needles are constantly covered with new layers of litter, the study of the forest litter from its upper boundary to the soil makes it possible to judge the change in biota over time. Succession occurs gradually, however, it can be divided into three stages:
- the first. It lasts about 6 months, during which the first stage of decomposition of the needles takes place. However, up to 50% of live pine needles are already affected by the Coniosporium fungus, which opens this succession. After the needles fall, this fungus quickly disappears, and Fusicoccum and Pullularia settle on it. At the end of the stage, Desmazierella develops en masse;
- the second. Lasts two years. In addition to Desmazierella, the participants in the succession include Sympodiella and Helicoma, to which soil mites are added;
- the third. The longest, which lasts 7 years. The main destructors of needles are soil animals - springtails, mites and oligochaetes-enchytreids. The needles are compressed, after which the intensity of decomposition decreases sharply and succession enters the stage of "climax".
Another example is the succession of the composition of xylophagous insects involved in the decomposition of wood. Five stages of this succession are distinguished (Kashkarov, 1944) with their population of detritivores: living wood, weakened wood, dead whole tree, partially decomposed wood, completely decomposed wood.
Heterotrophic succession can be demonstrated in an experiment on hay solution, where at first a lush culture of various bacteria blooms, which, when pond water is added, are replaced by protozoa of the genera Hypotricha, Amoeba, Vorticella. After the resources are exhausted, succession stops, and the organisms participating in it go into a dormant state.
test questions1. What successions are called heterotrophic?
2. Give an example of heterotrophic succession.
3. What experiment can illustrate heterotrophic succession?
12.6. Secondary autogenous (restorative) successions
Restorative successions by their nature do not differ much from primary ones, but, as noted, they occur in ecosystems that are partially or completely disturbed by external influences (usually by human activity). They usually proceed faster than the primary ones, their speed is affected by the degree of preservation of the ecosystem and the availability of sources of diasporas for its restoration.
A classic example of such a succession is the restoration of a steppe or forest on the site of an abandoned arable land. Approximately 150 years ago, the main systems of agriculture in Russia were fallow-shifting and slash-and-burn (respectively, in the steppe and forest zones). A piece of land was used as arable land for 5-10 years, after which it was abandoned, because the soil was depleted and weeds developed abundantly, representing the first stage of restorative succession already under the canopy of a cultivated plant. Man did not know how to control weeds in the absence of tractors and pesticides.
Gradually, on an abandoned field, through the stages of field (segetal) weeds, which dominated in the first year, and ruderal species that grew in the next 3-5 years, a steppe herbage was formed or a forest grew. During this succession, soil fertility was restored, and weeds were replaced by more powerful ruderal, meadow, and forest species. Accordingly, the fauna was also enriched.
The restoration of vegetation on the fallows took a long time - at least 25 years. Man has learned to speed up this process. J. Curtis in the twenties of the last century restored the prairies much faster due to "artificial seed rain" - a mixture of seeds collected on the remaining sections of the prairie. Restoration of meadows by sowing a mixture of seeds collected in natural grassland communities is practiced today in England.
The Stavropol botanist D. Dzybov developed an economical method for accelerating restorative succession by seeding hay from a virgin steppe area onto plowed soil. Seeds fall into the soil, and the succession of the steppe restoration accelerates sharply: by the fifth year, up to 80% of plant species of the virgin steppe already exist in such an “agrosteppe”. Nitrogen fertilizers were used to accelerate the recovery successions of Alaskan tundra ecosystems disturbed by oil extraction.
Restorative successions actively proceed not only on fallows, but also in crops of perennial grasses. This allows the use of old-growth crops of perennial grasses to increase the biological diversity of agricultural ecosystems.
It goes without saying that the entire heterotrophic biota of the ecosystem changes in the course of restorative successions. The literature provides data on changes in the fauna of birds, rodents, and insects.
The succession of bird population composition has been studied in the US prairies (Odum, 1986). The number of species of nesting birds varied from 15 to 239, and at different stages of succession, the composition of the bird population changed significantly:
– at the first stage (the first three years), when herbaceous plants dominated, the number of bird species varied from 15 to 40 species, with the common sparrow and meadow troupial dominating;
- at the second stage - shrubs, which lasted 22 years, the avifauna increased to 136 species, and the most massive were: American warbler, bunting, yellow-breasted warbler;
- at the third stage - the pine forest, which represented 35-100 years of succession, the avifauna was the richest and reached 239 species. The most massive were woodweed, tonagra, tyrant, yellow-fronted verion;
- at the final stage - oak-hickory forest, which is formed 150-200 years after the abandonment of arable land, the diversity of the bird population has decreased to 228 species. The American cuckoo, two more tree species and the green tyrant are added to the pine forest species.
M.N. Kerzina (1956). So the restoration of the spruce forest (Kostroma region) was accompanied by a change in the fauna of rodents and insects. At the stage of an open felling area (1–2 years after felling), the rodent fauna was represented by species of the genus Microtus, which were replaced by typical forest rodent species of the genus Clethrionomys during forest restoration, and at the middle stage of succession these species combined. The dynamics of insects also had a similar character (Table 12). In general, the entomofauna was depleted due to a sharp decrease in the number of cicadas, the number of individuals of other groups decreased, excluding spiders, the number of which increased.
Table 12 Population dynamics of the main groups of insects during the restoration of spruce, spruce-fir and pine forests (per 100 net sweeps; after M.N. Kerzina, 1956)
A common variant of secondary restorative succession is post-pasture demutation. With a decrease in pasture load, the process of restoration of tall grasses affected by grazing begins: meadow fescue, team hedgehog and awnless brome - in meadows and feather grass - in the steppes. Pasture patients (plantain, dandelion, goose cinquefoil, creeping clover in the meadow; Austrian wormwood and fescue in the steppe), in the absence of strong grazing, lose their competitive advantages and sharply reduce abundance.
Secondary restorative successions include a change in the aquatic ecosystem as a result of deeutrophication after the supply of nutrients to the ecosystem with runoff has ceased. Such successions were studied on Lake Washington by the prominent American ecologist T. Edmondson (1998). In the course of the described succession, abundantly multiplying cyanobacteria are gradually replaced by green and diatom algae and, in parallel, the biodiversity of zooplankton and nekton (fish) increases. Excess nutrients absorbed by planktonic organisms, after their death, settle to the bottom of the reservoir and are buried in sapropel.
After a decrease in the content of nutrients, the aquatic ecosystem is restored. Birds carry seeds of aquatic plants and fish eggs.
test questions1. What successions are classified as secondary autogenous (restorative)?
2. Describe the restorative succession of a plant community using a specific example.
3. Give examples of changes in the heterotrophic biota of an ecosystem in the course of restorative succession.
4. How do successions of deeutrophication of aquatic ecosystems proceed?
12.7. Allogeneic successions
Allogeneic successions are caused by factors external to ecosystems. Such successions most often occur as a result of human influence, although natural allogeneic changes are also possible. Their example is the change in the composition of the floodplain ecosystem as a result of the meandering of the river and the deepening of the base of the channel erosion by it. As a result, the level of the floodplain rises, while the duration of flooding and the amount of silt decrease. As a result, communities of willow, poplar, elm and linden-oak forests successively replace each other in the floodplain ecosystems of the temperate zone, and the composition of herbaceous species changes completely. The composition of heterotrophic biota also changes, as plant communities provide them with an appropriate food base. In addition, the composition of the plant community reflects the duration of flooding during the flood period, which largely determines the possibility of survival of various species of insects, birds, soil fauna, etc.
The most common example of allogeneic succession is the change in grassland ecosystems (meadows and steppes) under the influence of grazing. With high pasture loads, species richness, biological production, and biomass decrease, and changes in the composition of the plant community and the fauna accompanying it occur: tall and well-eaten plants are replaced by stunted and poorly eaten plants (the latter can also be tall, such as, for example, thistle species - the genus Carduus). In steppe ecosystems, the stages of pasture digression are distinguished: feather grass, fescue (with Festuca valesiaca or F. pseudovina), wormwood with Artemisia austriaca dominating. At the final stages of such a succession, ruderalization occurs and annuals develop massively, which use breaks between grazing cycles and conditions of weakened competition with perennials that are oppressed by grazing for rapid growth.
Today, an extremely common and undesirable process of changing aquatic ecosystems is their eutrophication - a change as a result of the influx of a large number of mineral nutrients, primarily phosphorus. The main cause of eutrophication is the washout of fertilizers from fields, as well as runoff from livestock farms.
In the course of succession, diatoms die first, followed by green algae, which are replaced by cyanobacteria. Some strains of cyanobacteria release toxic substances into the water that cause the death of many organisms. When sinking to the bottom, they are decomposed by decomposers, which requires a large amount of oxygen. As a result, in such an oxygen-depleted water body, most species of fish and macrophytes die (primarily those demanding clean water, such as salvinia, frog watercress, highlander amphibian). At the same time, hornwort, cattail broadleaf and duckweed can withstand a fairly high level of pollution and survive in such a eutrophicated ecosystem. A bad smell is felt around the eutrophicated reservoir, brown foam containing dead plankton accumulates in shallow water.
If the amount of runoff is limited or has already been stopped, the aquatic ecosystem itself can cope with pollution - the process of deeutrophication will occur, described in the previous section. Macrophytes that actively assimilate nutrients can successfully resist eutrophication.
However, the self-cleaning capacity of aquatic ecosystems is limited, and therefore if runoff flows for a long time and in large quantities, they die.
Eutrophication should be distinguished from the poisoning of aquatic ecosystems by industrial and domestic effluents that contain toxic substances, such as heavy metals. If the supply of toxicants is limited, then the ecosystem can cope with them: toxic substances will enter the organisms of its inhabitants, and after their death they will be buried at the bottom. At the bottom of the reservoirs of the Kuibyshev, Volgograd and other reservoirs, a multi-meter layer of toxic sediments has accumulated, formed in the process of self-purification.
However, if a significant amount of toxic substances comes in, and even more so if they come in regularly, the aquatic ecosystem will not be able to recover.
Another example of allogeneic succession is the change in the composition of ecosystems under the influence of radiation. They were studied by R. Whittaker and G. Woodwell (Whittaker, Woodwell, 1972) at the radiation test site on. Long (USA). With an increase in the dose of radiation (a source of gamma radiation was used), a succession occurred, which was, as it were, a mirror image of the succession of overgrowing rocks described by F. Clements: first, trees died, then shrubs, grasses, mosses, and at the highest doses of radiation, only soil algae remained. . In the Chernobyl region, after the accident, succession passed the first stage: in the forests located near the nuclear power plant, the forest stand dried up (however, after a few years, it began to recover intensively).
As a rule, allogeneic successions are accompanied by a decrease in productivity and biodiversity, although these parameters may increase in the early stages of succession. Grass communities with moderate grazing, forests with some influence from campers, or aquatic ecosystems with light eutrophication have a richer species composition than the same communities without external influences.
In some cases, during allogeneic succession, production increases, but species richness decreases. This is observed when meadows change under the influence of mineral fertilizers: the number of species in communities decreases by 2-2.5 times. The reason for this is the intensification of competition with an increase in the level of resource provision. So much damage to the species composition of European mountain meadows on poor soils was caused by measures to improve them by applying mineral fertilizers. Similarly, a decrease in species richness can be accompanied by an increase in biological production during eutrophication of water bodies.
test questions1. Tell us about changes in ecosystems under the influence of intensive grazing.
2. What changes occur in aquatic ecosystems during eutrophication?
3. How do high doses of radiation affect ecosystems?
12.8. natural evolution of ecosystems
The difference between the evolution of ecosystems and successions lies in the fact that in the course of evolution new combinations of species appear and new mechanisms for their coexistence are developed. The result of natural evolution is the diversity of ecosystems, which was discussed in Chapter 11. Unlike organisms, ecosystems and their biota as a whole do not evolve. The evolution of ecosystems proceeds as a grid-like process, which consists of more or less independent evolution of the species that make up them (Whittaker, 1980).
For organisms of the same trophic level, the main mechanism of evolution is diversification, i.e. increased dissimilarity of species - evolution is not “towards”, but “from”, which allows species to occupy different ecological niches and coexist stably in the community. The principle of dividing ecological niches softens competition and can be supplemented by the already considered mechanisms of mutual (as in family groups of animals) or unilateral favoring (as in nurse plants and their wards).
Co-adaptation of the “plant-phytophage” and “predator-prey” relationships often have a diffuse (collective) character: it is not individual species (species A–species B) that adapt to each other, but entire guilds (“teams”). For example, in the savannah, "teams" of herbs and herbivores, woody plants and twig-eaters adapt to each other. Of course, adaptation in this case does not mean mutual assistance, but a decrease in the intensity of antagonistic relations.
test questions1. What role does species diversification play in ecosystem evolution?
2. Tell us about the role of species unification for their coexistence.
3. What is diffuse coadaptation?
12.9. anthropogenic evolution of ecosystems
The natural evolution of ecosystems takes place on a millennium scale, at present it is suppressed by anthropogenic evolution associated with human activities. The biological time of anthropogenic evolution has a scale of decades and centuries.
Anthropogenic evolution of ecosystems is divided into two large classes (according to the type of processes): purposeful and spontaneous. In the first case, a person forms new types of artificial ecosystems. The result of this evolution are all agro-ecosystems, garden and park ensembles, sea gardens of brown algae, oyster farms, etc. However, "unplanned" processes are always added to the "planned" evolution - spontaneous species are introduced, for example, weed plant species and phytophagous insects into agrocenoses. A person seeks to suppress these "unplanned" processes, but this turns out to be practically impossible.
The spontaneous anthropogenic evolution of ecosystems plays a greater role than the purposeful one. It is more diverse and, as a rule, has a regressive character: it leads to a decrease in biological diversity, and sometimes productivity.
The basis of spontaneous anthropogenic evolution is the appearance in ecosystems of species that are unintentionally (rarely intentionally) introduced by humans from other areas. The scale of this process is so great that it took on the character of the "great migration" and "homogenization" of the biosphere under the influence of man (Lodge, 1993). Alien species are called adventitious (Kornas, 1978, 1990), and the process of introduction (invasion) of adventitious species into ecosystems is called adventivization.
The reason for the dispersal of adventitious species is the anthropogenic disruption of the processes of self-regulation of ecosystems in the absence of antagonist species (Elton, 1960), as in the North American prickly pear in Australia and the Amazonian water hyacinth in Africa and Asia, or, on the contrary, when a pathogen species appears, to which the local the host species is not immune, as in the stories of the death of Castanea dentata and the destruction of African savannahs by cowdisease virus (see 8.5).
"Ecological explosions" cause the introduction of species that turn out to be key. More often, such "explosions" do not occur at all, since the adventitious species does not displace native species from the community at all, or if it displaces, then it assumes the functional role of the displaced species.
In the process of anthropogenic evolution, some species of local flora and fauna, which turned out to be pre-adapted to the regime of increasing anthropogenic loads, may also increase. In the past, they were associated with places of local natural disturbances - mountain mudflows, burrows, trampled areas of ecosystems near watering places, rookeries of large phytophages, such as bison or bison, etc.
The result of the anthropogenic evolution of ecosystems, in addition, is:
– destruction of species or reduction of their genetic diversity (the number of pages in the Red Data Books in all countries increases year by year);
- displacement of the boundaries of natural zones - the development of the process of desertification in the steppe zone, the displacement of forests by grassy vegetation near the southern border of their distribution;
– the emergence of new ecosystems that are resistant to human influence (for example, ecosystems of downtrodden pastures with depleted species richness);
– formation of new communities on anthropogenic substrates during their natural overgrowth or reclamation.
However, the basis of anthropogenic evolution today, of course, is the process of dispersal of alien species, called adventivization. This issue is so relevant that it is specifically considered in the next section.
test questions1. What is the difference between purposeful and spontaneous varieties of anthropogenic evolution of ecosystems?
2. Give examples of "environmental explosions" during the anthropogenic evolution of ecosystems.
3. What are the results of the anthropogenic evolution of ecosystems?
12.10. The scale of the adventivization process of the biosphere
Adventitious species include representatives of almost all groups of the organic world, although adventitious plant species are the most studied.
Plants were settled by man during any migrations (nomadic camps, military campaigns, trade routes, etc.). However, the migration of plants from mainland to mainland became especially active after the discovery of America by Columbus. At the same time, the flow of plants from the Old World to the New World turned out to be more powerful than in the opposite direction. There are phenomena of "Africanization" of the American savannas (White, 1977) and "Europeanization" of the Mediterranean communities of California (Noe and Zedler, 2001). The first episode was associated with an increase in the flow of diasporas from Africa with hay, on which black slaves slept in the holds, and the simultaneous destruction of the grass layer of the savannas under the influence of cattle. Under these conditions, African grasses Hypperhenia ruta, Panicum maximum, Brachiaria mutica became widespread. In California, most species from natural annual grasslands have been replaced by European Bromus mollis and Lolium multiflorum.
To date, the pattern of adventitization of floras on different continents is as follows (Lonsdale, 1999): North America - 19%, Australia - 17%, South America - 13%, Europe - 9%, Africa - 7%, Asia - 7%. Maximum share of S.v. identified in agricultural and urban ecosystems - 31%, followed by temperate forests, in the flora of which the share of Z.v. reaches 22%. The biome of Mediterranean sclerophyte shrubs also contains a lot of Z.v. - 17%. This indicator sharply decreases in alpine vegetation (11%), in savannahs (8%) and deserts (6%). Adventive species are found in the flora of any reserve, except for Antarctica (where there are no plants at all).
Among the adventitious species are most of the weed species that were transported from area to area with cultivated plants, as well as many ruderal plants that spread when natural ecosystems were disturbed by humans. In the south-east of the European part of Russia, aggressive ruderal species from the genera Ambrosia and Cyclachene are rapidly settling, which form pure thickets.
Aquatic adventive species are especially easy to disperse. IN last years in many reservoirs of the tropical and subtropical zones, water hyacinth and importunate salvinia have massively settled. They cause significant economic damage, especially in Africa, Southeast Asia and Australia. In the irrigation canals of Europe, the Canadian elodea causes great harm, and in the reservoirs of Canada, the European urut has grown there. In the irrigation systems of the United States, the African plant alligator grass delivers a lot of trouble. In Australia, rice fields are overgrown with chicken millet introduced from Asia.
ecosystem mediterranean sea the tropical alga Caulerpa, which releases potent toxins into the water, causes damage (apparently, Caulerpa was introduced with ballast water, although it is possible that aquarists were the perpetrators of its settlement).
The picture of the distribution of adventitious animal species is less complete. Among them there are many dangerous species that, due to the lack of natural enemies that control their numbers, can cause significant damage to ecosystems. The effects of rabbit naturalization in Australia are well known.
In recent years, the ecosystems of the Black, Azov and Caspian Seas have been suffering from ctenophores, an invertebrate animal introduced with ship ballast water. The comb jelly eats eggs and juveniles of fish.
The ecosystems of the North American Great Lakes are being altered by the European perch, which is a voracious eater of juvenile native fish species. Great damage to these ecosystems (as well as to ships and industrial enterprises) is caused by exotic species mollusks (in particular, zebra mussel, which was brought from Europe). Rapidly multiplying, they clog water pipes and stick around the bottoms of ships.
In Lake Issykkul, a low-value aggressive species of Eleotris fish, brought from the Far East, has recently appeared, and the Far Eastern rotan, eating juvenile fish, has long settled along the rivers and lakes of the Moscow region. In recent years, he settled in the upper Volga (already registered near the city of Saratov).
In general, the process of adventivization of ecosystems became especially active after 1950 due to the rapid development of vehicles, and after 1970 due to the development of market and economic globalization processes. After 2030, adventivization is predicted to increase due to climate warming (di Castri, 1990). However, climate warming may affect different biomes differently. Tundra ecosystems, for example, have a high buffering capacity, and therefore, with climate warming, their invasive potential may remain the same due to the fact that the ratio between species in communities will change: the role of vascular plants will increase, while the role of spore plants will decrease.
An analysis of the consequences of anthropogenic evolution shows that man should be careful when introducing a species from one area to another, and more cautious in cases where unintentional introduction of species may occur, and take action against already spread invasive species if they adversely affect natural ecosystems.
test questions1. What historical event is considered as the beginning of intensive adventivization of flora and fauna?
2. Tell us about the Africanization of the American savannas and the Europeanization of the grasslands of California.
3. Give a general picture of the current level of flora adventivization on a global scale.
4. Give examples of the detrimental impact on ecosystems of adventitious animal species.
5. What factors will contribute to the process of anthropogenic homogenization of the biosphere in the future?
Topics of reports at seminars1. The importance of the cyclical dynamics of ecosystems for maintaining their sustainability.
2. Development of F. Clements' views on the nature of ecological succession.
3. Opportunities to use the potential of restorative successions for the conservation of ecosystems.
4. Allogeneic successions as a factor in the destruction of the biosphere.
5. Natural and anthropogenic branches of ecosystem evolution: comparison and assessment of the contribution to biosphere change.
Chapter 13
When considering ecosystems, we talked about the flows of energy and matter. To characterize the process of energy transformation, we cited the “Lindemann law” (the 10% rule) and discussed deviations from this law, but the patterns of cyclic circulation of substances have not yet been discussed. This was done deliberately: with the spatial uncertainty (ranklessness) of ecosystems, it is impossible to talk about the cycles of substances within one ecosystem. For this reason, we consider the circulation of substances only in the largest ecosystem - the biosphere.
The origins of ideas about the biosphere go to the works of A. Lavoisier, J.B. Lamarck and BUT. Humboldt (see 1.1), however, the term "biosphere" was proposed by the Austrian scientist E. Suess in 1875. With this term, he designated one of the shells of the Earth - the space in which there is life. The holistic doctrine of the biosphere was created by the Russian scientist V.I. Vernadsky (1926), who substantiated the geological transformative role of living organisms. They are the main geological force that created the biosphere and maintains its state at the present time. Close to the concept of "biosphere" is the concept of "gay" (from the Greek. Gaia - the goddess of the Earth), which in the 70s. of our century was proposed by the English scientist J. Lovelock.
13.1. Biosphere as a shell of the Earth
In addition to the biosphere, Suess identified three more shells - atmosphere, hydrosphere And lithosphere.
Atmosphere- the outermost gaseous shell of the Earth, it extends to a height of 100 km. The main components of the atmosphere are nitrogen (78%), oxygen (20.95%), argon (0.93%), carbon dioxide (0.03%). The atmosphere is partly a product of the vital activity of organisms, since atmospheric oxygen is the result of the activity of photosynthetic organisms - cyanobacteria and plants. At an altitude of 20-45 km, the ozone layer is located, the ozone content in it is approximately 10 times higher than in the atmosphere near the Earth's surface. This layer protects the surface of the planet from excess ultraviolet rays that adversely affect living organisms.
Between the atmosphere and the earth's surface there is a constant exchange of heat, moisture and chemical elements.
The state of the atmosphere is affected by human economic activity, due to which methane, nitrogen oxides and other gases appeared in it, causing atmospheric processes - the greenhouse effect, the destruction of the ozone layer, acid rain, smog.
Hydrosphere turns out to be not a continuous shell: the seas and oceans cover the Earth only by 2/3, the rest is occupied by land. On land, the hydrosphere is represented in fragments - lakes, rivers, groundwater (Table 13).
Table 13 Distribution of water masses in the Earth's hydrosphere (according to Lvovich, 1986)
The hydrosphere is 94% represented by the salty waters of the oceans and seas, and the contribution of rivers to the planet's water budget is 10 times less than the amount of water vapor in the atmosphere. Three-quarters of fresh water is inaccessible to organisms, as it is conserved in the glaciers of the mountains and the polar caps of the Arctic and Antarctica.
The hydrosphere is experiencing an ever-increasing influence of human economic activity, which leads to a violation of the biospheric water cycle considered below (acceleration of the melting of glaciers, a decrease in the amount of liquid fresh water and an increase in vaporous water as a result of evaporation from reclaimed agroecosystems.
Lithosphere- this is the upper solid shell of the Earth, the thickness of which is 50-200 km. The top layer of the lithosphere is called the earth's crust. The substances that make up the lithosphere are partly formed due to the activity of organisms, and this is not only peat, coal, oil shale, but also the much more common calcium carbonate formed from mollusks and other marine animals. A completely special environment is the soil (see 2.6), located on the border of the lithosphere and atmosphere.
At present, man has the strongest technogenic influence on the lithosphere, especially due to the development of erosion processes, an increase in solid runoff, the burning of fossil fuels and the creation of engineering structures. Artificial (technogenic) soils already cover more than 55% of the Earth's land area, and in a number of urban areas (Europe, Japan, Hong Kong, etc.) they cover 95-100% of the territory and their thickness reaches several tens of meters. The total area covered by all types of engineering structures (buildings, roads, reservoirs, canals, etc.) in 2000 reached 1/6 of the land area.
The biosphere covers the entire hydrosphere, part of the atmosphere and part of the lithosphere. Its upper boundary is located at an altitude of 6 km above sea level, the lower one is at a depth of 15 km in the Earth's crust (bacteria in oil waters live at such a depth) and 11 km in the ocean. Compared to the diameter of the Earth (13,000 km), the biosphere is a thin film on its surface. However, the main life in the biosphere is concentrated within much narrower limits, covering only a few tens of meters on the continents, in the atmosphere and in the ocean (Table 14).
Table 14 The structure of the biomass of the biosphere (dry matter)
In the biosphere there is a cycle of all substances, i.e. their repeated participation in the processes of synthesis and destruction of organic matter. Virtually all chemical elements, however, the most important for the biosphere are the cycles of water, oxygen, carbon, nitrogen, phosphorus.
test questions1. With the names of which scientists is the birth and development of the concept of the biosphere associated?
2. Name the shells of the Earth, which were identified by E. Suess.
3. Tell us about the composition of the atmosphere.
4. What is the structure of the hydrosphere?
5. Describe the scale of technogenic disturbances of the lithosphere by man.
6. Name the upper and lower boundaries of the biosphere.
13.2. The main cycles of substances in the biosphere
The most important characteristic of the biosphere is the cycles of substances occurring in it, which are due to biogenic and abiogenic causes. Currently, they are disturbed by human economic activity, which leads to a violation of the biosphere and can have serious consequences for future generations of earthlings. Consider the cycles of the most important nutrients - carbon, oxygen, nitrogen, water.
13.2.1. The carbon cycle
This is one of the most important biospheric cycles, since carbon is the basis of organic matter. The role of carbon dioxide is especially great in the cycle (Fig. 23).
Rice. 23. Carbon cycle in the biosphere.
The reserves of "living" carbon in the composition of land and ocean organisms are, according to various sources, 550-750 Gt (1 Gt equals 1 billion tons), with 99.5% of this amount concentrated on land, the rest in the ocean. In addition, the ocean contains up to 700 Gt of dissolved organic matter.
The reserves of inorganic carbon are much larger. Above every square meter of land and ocean is 1 kg of atmospheric carbon, and under each square meter of ocean at a depth of 4 km - 100 kg of carbon in the form of carbonates and bicarbonates. Even more carbon reserves are in sedimentary rocks - limestone contains carbonates, shale contains kerogens, etc.
Approximately 1/3 of the "live" carbon (about 200 Gt) circulates, i.e. annually assimilated by organisms in the process of photosynthesis and returned back to the atmosphere, and the contribution of the ocean and land to this process is approximately the same. Although ocean biomass is much smaller than land biomass, its biological production is generated by many generations of short-lived algae (the ratio of biomass to biological production in the ocean is about the same as in a freshwater ecosystem, see 11.1).
Up to 50% (according to some sources - up to 90%) of carbon in the form of dioxide is returned to the atmosphere by soil decomposer microorganisms. Bacteria and fungi contribute equally to this process. The return of carbon dioxide during the respiration of all other organisms is thus less than during the activity of decomposers.
Some bacteria, in addition to carbon dioxide, form methane. The release of methane from the soil increases with waterlogging, when anaerobic conditions are created that are favorable for the activity of methane-forming bacteria. For this reason, the release of methane from forest soil sharply increases if the forest stand is cut down and, due to a decrease in transpiration, its waterlogging occurs. A lot of methane is emitted by rice fields and livestock.
Currently, there is a violation of the carbon cycle due to the burning of a significant amount of fossil carbonaceous energy carriers, as well as during the dehumification of arable soils and the drainage of marshes. In general, the content of carbon dioxide in the atmosphere increases by 0.6% annually. The content of methane increases even faster - by 1-2%. These gases are the main contributors to the increased greenhouse effect, which is 50% dependent on carbon dioxide and 33% on methane.
The consequences of the increased greenhouse effect for the biosphere are unclear, the most likely forecast is climate warming. However, since the "machines" of climate are sea currents, as a result of their change during the melting of glaciers, a significant cooling is possible in a number of areas (including in Europe as a result of a change in the Gulf Stream). Under the influence of changes in the concentration of carbon dioxide, major natural disasters (floods, droughts, etc.) are significantly more frequent.
The given data characterize the biogenic carbon cycle. The cycle also involves geochemical processes, in which there is an exchange of atmospheric carbon and carbon contained in rocks. However, there are no data on the rate of these processes. It is only believed that their intensity has changed in the history of the planet and the greenhouse effect that is observed today has repeatedly manifested itself in the past with the intensification of geochemical processes with the release of carbon dioxide and the weakening of the processes that “pulled” it out of the atmosphere.
In order to bring the carbon cycle back into balance, it is necessary to increase the area of forests and reduce the emission of gases from the combustion of carbonaceous energy carriers.
test questions1. What is the ratio of the amount of "living" carbon on land and in the ocean?
2. What is the ratio of the amount of "dead" carbon in the atmosphere and in the ocean?
3. What proportion of "living" carbon is annually involved in the cycle?
4. What proportion of carbon is returned to the atmosphere by decomposers of terrestrial ecosystems?
5. List the factors that disrupt the carbon cycle.
6. What are the consequences of an increase in the greenhouse effect?
13.2.2. The water cycle
Water evaporates not only from the surface of reservoirs and soils, but also from living organisms, whose tissues are 70% water (Fig. 24). A large amount of water (about 1/3 of all precipitation water) is evaporated by plants, especially trees: they spend from 200 to 700 liters of water to create 1 kg of organic matter in different areas.
Rice. 24. Water cycle in the biosphere.
Different fractions of water in the hydrosphere participate in the cycle in different ways and at different rates. Thus, the complete renewal of water in the composition of glaciers occurs in 8 thousand years, groundwater - in 5 thousand years, the ocean - in 3 thousand years, soil - in 1 year. Atmospheric vapors and river waters are completely renewed in 10-12 days.
Before the development of civilization, the water cycle was balanced, but in recent decades, human intervention has disrupted this cycle. In particular, the evaporation of water from forests decreases due to the reduction in their area, and, on the contrary, evaporation from the soil surface increases during the irrigation of agricultural crops. Evaporation of water from the surface of the ocean is reduced due to the appearance of a large part of the oil film on it. Climate warming caused by the greenhouse effect affects the water cycle. With the strengthening of these tendencies, significant changes in the cycle can occur, which are dangerous for the biosphere.
The ocean plays an important role in the annual water balance of the biosphere (Table 15). Evaporation from its surface is about twice as much as from the land surface.
Table 15 The annual water balance of the Earth (according to Lvovich, 1986)
test questions
1. How much does the ocean contribute to the evaporation of water?
2. What contribution do plants make to water evaporation?
3. How fast is the circulation of different fractions of water?
4. Tell us about the reasons for the violation of the water cycle.
13.2.3. nitrogen cycle
The circulation of nitrogen in the biosphere proceeds according to the following scheme (Fig. 25):
– conversion of inert nitrogen of the atmosphere into forms accessible to plants (biological nitrogen fixation, formation of ammonia during lightning discharges, production of nitrogen fertilizers at factories),
- absorption of nitrogen by plants,
- the transfer of part of the nitrogen from plants to animal tissues,
– accumulation of nitrogen in detritus,
– decomposition of detritus by decomposer microorganisms up to the reduction of molecular nitrogen, which is returned to the atmosphere
Rice. 25. Nitrogen cycle in the biosphere.
In marine ecosystems, nitrogen fixers are cyanobacteria that fix nitrogen into ammonia, which is absorbed by phytoplankton.
Currently, due to a decrease in the share of natural ecosystems, biological nitrogen fixation has become less than industrial nitrogen fixation (90-130 and 140 million tons per year, respectively), and by 2020, an increase in industrial nitrogen fixation by 60% is expected. Up to half of the nitrogen applied to the fields is washed into groundwater, lakes, rivers and causes eutrophication of water bodies.
A significant amount of nitrogen in the form of nitrogen oxides enters the atmosphere, and then into the soil and water bodies as a result of its pollution by industry and transport (acid rain). This nitrogen was withdrawn from the atmosphere by the ecosystems of the geological past and for a long time was "deposited" in coal, gas, oil, when burned, it returns to the circulation. For example, in the United States, 20-50 kg/ha of nitrogen falls with atmospheric precipitation per year, and in some areas the emission reaches 115 kg/ha.
The amount of nitrogen emission of 10-30 kg/ha per year is considered environmentally safe. At higher loads, significant changes occur in ecosystems: soils become acidified, nutrients are leached into deep horizons, forest stands may dry out and the mass development of alien nitrophilic species is possible. In addition, the high content of nitrogen in plants grown on nitrogen-contaminated soils increases their palatability, which can lead to the loss of even dominant species from plant communities. So, in some wastelands of Western Europe, after the nitrogen content increased in the heather, the heather beetle multiplied en masse (its number reached 2000 specimens per 1 m 2). The beetle almost completely ate this shrub out of the communities. The same changes in the composition of communities polluted by industrial nitrogen were noted in California.
However, acid rain does not always have a detrimental effect on ecosystems. The ecosystems of the steppe zone, where soils have a slightly alkaline reaction, not only do not suffer from acid rain, but even increase their productivity due to additional nitrogen.
Restoration of the natural nitrogen cycle is possible by reducing the production of nitrogen fertilizers, a sharp reduction in industrial emissions of nitrogen oxides into the atmosphere and expanding the area under legumes, which are symbiotically associated with nitrogen-fixing bacteria.
test questions1. List the main stages of the nitrogen cycle.
2. Through what channels does atmospheric nitrogen enter ecosystems?
3. What contribution does technogenic nitrogen make to the cycle?
4. Tell us about the contribution to the nitrogen cycle of burning nitrogen-containing energy carriers.
5. What should be done to normalize the nitrogen cycle?
13.2.4. Oxygen cycle
Atmospheric oxygen is of biogenic origin and its circulation in the biosphere is carried out by replenishing reserves in the atmosphere as a result of plant photosynthesis and absorption during the respiration of organisms and fuel combustion in the human economy (Fig. 26). In addition, a certain amount of oxygen is formed in the upper layers of the atmosphere during the dissociation of water and the destruction of ozone under the action of ultraviolet radiation, and part of the oxygen is spent on oxidative processes in the earth's crust, during volcanic eruptions, etc.
Rice. 26. Oxygen cycle in the biosphere.
This cycle is very complex, since oxygen enters into various reactions and is part of a very large number of organic and inorganic compounds, and is slow. It takes about 2 thousand years to completely renew all the oxygen in the atmosphere (for comparison: about 1/3 of the atmospheric carbon dioxide is renewed annually).
Currently, an equilibrium oxygen cycle is maintained, although local disturbances occur in large densely populated cities with a large number of transport and industrial enterprises.
However, there has been a deterioration in the state of the ozone layer and the formation of "ozone holes" (areas with a low ozone content) above the Earth's poles, which poses an environmental hazard. Temporary "holes" also appear over vast areas outside the poles (including over the continental regions of Russia). The reason for these phenomena is the ingress of chlorine and nitrogen oxides into the ozone layer, which are formed in the soil from mineral fertilizers when they are destroyed by microorganisms, and are also found in car exhaust gases. These substances destroy ozone at a faster rate than it can be formed from oxygen under the influence of ultraviolet rays.
The preservation of the ozone layer is one of the global tasks of the world community. To stop the destruction of the ozone layer and restore it, it is necessary to abandon the use of chlorine-containing substances - chlorofluorocarbons (freons) used in aerosol packages and refrigeration units. It is also necessary to reduce the amount of exhaust gases from internal combustion engines and the doses of nitrogen mineral fertilizers in agriculture.
The ozone content can increase in the surface layer of the atmosphere, since ozone is a photo-oxidant formed from nitric oxide and hydrocarbons under the influence of ultraviolet rays. In this case, it turns out to be a dangerous pollutant that causes irritation of the human respiratory tract. However, the excessively low content of ozone in the atmosphere also adversely affects human health.
test questions1. Name the main source of oxygen replenishment in the atmosphere.
2. Indicate the processes in which oxygen is absorbed from the atmosphere.
3. How long does it take to update the supply of oxygen in the atmosphere?
4. Describe the problem of preserving the ozone layer of the atmosphere.
13.2.5. Phosphorus cycle
It is possible to speak about the cycle of phosphorus for the foreseeable time only conditionally. Being much heavier than carbon, oxygen and nitrogen, phosphorus almost does not form volatile compounds - it flows from land to the ocean, and returns mainly when the land rises during geological transformations. For this reason, the phosphorus cycle is called "open" (Fig. 27).
Rice. 27. Cycle of phosphorus in the biosphere.
Phosphorus is found in rocks, from where it is leached into the soil and absorbed by plants, and then it passes through the food chains to animals. After the decomposition of the dead bodies of plants and animals, not all phosphorus is involved in the cycle, part of it is washed out of the soil into water bodies (rivers, lakes, seas). There, phosphorus settles to the bottom and almost never returns to land, only a small amount of it returns with fish caught by humans or with the excrement of birds that feed on fish. Accumulations of excrement of seabirds served in the recent past as a source of the most valuable organic fertilizer - guano, but at present the resources of guano are practically exhausted.
The outflow of phosphorus from land to the ocean increases due to an increase in surface water runoff due to the destruction of forests, plowing of soils and the introduction of phosphorus fertilizers. Since phosphorus reserves on land are limited, and its return from the ocean is problematic (although the possibilities of extracting it from the ocean floor are currently being actively explored), in the future, an acute shortage of phosphorus is possible in agriculture, which will cause a decrease in yields (primarily grain). Therefore, it is necessary to conserve phosphorus resources.
test questions1. Why is the phosphorus cycle called open?
2. Where are phosphorus reserves concentrated?
3. Why is phosphorus concentrated at the bottom of the oceans?
4. What are the consequences for agriculture of the depletion of phosphorus reserves.
13.3. Noosphere
In conclusion of the chapter, it is necessary to say a few words about the commonly used (especially on the pages of popular "green" environmental publications) term "noosphere", which was independently introduced into environmental use by P. Terjar de Chardin and V.I. Vernadsky. However, if Terjar de Chardin understood the noosphere primarily as the global development of the "collective mind", then Vernadsky believed that this "collective mind" should transform the biosphere, improving the conditions for human life on the planet.
Vernadsky proceeded from a scientistic view of the relationship between man and nature, i.e. believed that science could solve almost any problem, up to managing the basic cycles of substances and the transition of a person to "autotrophic nutrition" with the direct use of solar energy for food production (bypassing the intermediary role of plants).
Vernadsky's views on the noosphere are an example of ecological utopianism. The system of connections in the biosphere (“the biosphere market”) is so complex that a person cannot manage it. Serious interventions in biospheric cycles lead to a sharp aggravation of the ecological situation, which is already observed today (destruction of the ozone screen, climate warming, global environmental pollution, the emergence of new "environmental diseases", etc.).
Man can survive only together with the biosphere, "embedding" his economic activity in the biospheric cycles. N.N. Moiseev wrote about the possibility of “co-adaptation of man and the biosphere” and the formation on this basis of a certain “quasi-stable state” of the latter, in which changes in the circulation of substances will not exceed threshold values, starting from which irreversible changes can occur. This new state of the biosphere is possible when building a world community of sustainable development, but consideration of this problem lies beyond the scope of general ecology.
Topics of reports at seminars1. The structure of the biosphere and its relationship with other shells of the Earth according to E. Suess.
2. The danger of anthropogenic disturbances in the circulation of substances in the biosphere.
3. Critical assessment of V.I. Vernadsky about the noosphere.
Ecosystems are unified natural complexes that are formed by a combination of living organisms and their habitats. The science of ecology is engaged in the study of these formations.
The term "ecosystem" appeared in 1935. The English ecologist A. Tensley suggested using it. A natural or natural-anthropogenic complex in which both living and indirect components are in close relationship through the metabolism and distribution of energy flow - all this is included in the concept of "ecosystem". The types of ecosystems are different. These basic functional units of the biosphere are divided into separate groups and studied by environmental science.
Origin Classification
There are various ecosystems on our planet. Types of ecosystems are classified in a certain way. However, it is impossible to link together the diversity of these units of the biosphere. That is why there are several classifications of ecological systems. For example, they distinguish them by origin. This:
- Natural (natural) ecosystems. These include those complexes in which the circulation of substances is carried out without any human intervention.
- Artificial (anthropogenic) ecosystems. They are created by man and can only exist with his direct support.
natural ecosystems
Natural complexes that exist without human intervention have their own internal classification. There are the following types of natural ecosystems on the basis of energy:
Completely dependent on solar radiation;
Receiving energy not only from the heavenly body, but also from other natural sources.
The first of these two types of ecosystems is unproductive. Nevertheless, such natural complexes are extremely important for our planet, since they exist over vast areas and influence climate formation, purify large volumes of the atmosphere, etc.
Natural complexes that receive energy from several sources are the most productive.
Artificial units of the biosphere
Anthropogenic ecosystems are also different. The types of ecosystems included in this group include:
Agro-ecosystems that appear as a result of human agriculture;
Technoecosystems resulting from the development of industry;
Urban ecosystems resulting from the creation of settlements.
All these are types of anthropogenic ecosystems created with the direct participation of man.
Diversity of natural components of the biosphere
Types and types of ecosystems of natural origin are different. Moreover, environmentalists distinguish them based on the climatic and natural conditions of their existence. So, there are three groups and a number of different units of the biosphere.
The main types of ecosystems of natural origin:
ground;
freshwater;
Marine.
Ground natural complexes
The variety of types of terrestrial ecosystems includes:
Arctic and Alpine tundra;
Coniferous boreal forests;
Deciduous massifs of the temperate zone;
Savannas and tropical grasslands;
Chaparrals, which are areas with dry summers and rainy winters;
Deserts (both shrub and grassy);
Semi-evergreen tropical forests located in areas with pronounced dry and wet seasons;
Tropical evergreen rain forests.
In addition to the main types of ecosystems, there are also transitional ones. These are forest-tundras, semi-deserts, etc.
Reasons for the existence of various types of natural complexes
By what principle are various natural ecosystems located on our planet? Types of ecosystems of natural origin are in one or another zone depending on the amount of precipitation and air temperature. It is known that the climate in different parts of the world has significant differences. At the same time, the annual amount of precipitation is not the same. It can range from 0 to 250 or more millimeters. In this case, precipitation either falls evenly throughout all seasons, or falls in the main share for a certain wet period. The average annual temperature also varies on our planet. It can have values from negative values \u200b\u200band reach thirty-eight degrees Celsius. The constancy of heating of air masses is also different. It may either not have significant differences during the year, as, for example, near the equator, or it may constantly change.
Characteristics of natural complexes
The variety of types of natural ecosystems of the terrestrial group leads to the fact that each of them has its own distinctive features. So, in the tundra, which are located north of the taiga, there is a very cold climate. This area is characterized by a negative average annual temperature and a change of polar day and night. Summer in these parts lasts only a few weeks. At the same time, the earth has time to thaw to a small meter depth. Precipitation in the tundra is less than 200-300 millimeters during the year. Due to such climatic conditions, these lands are poor in vegetation, represented by slow-growing lichens, moss, as well as dwarf or creeping lingonberry and blueberry bushes. At times you can meet
The animal world is not rich either. It is represented by reindeer, small burrowing mammals, and predators such as ermine, arctic fox and weasel. The world of birds is represented by a snowy owl, a snow bunting and a plover. Insects in the tundra are mostly Diptera species. The tundra ecosystem is very vulnerable due to poor resilience.
The taiga, located in the northern regions of America and Eurasia, is very diverse. This ecosystem is characterized by cold and long winters and abundant snowfall. The flora is represented by evergreen coniferous forests, in which fir and spruce, pine and larch grow. Representatives of the animal world - moose and badgers, bears and squirrels, sables and wolverines, wolves and lynxes, foxes and minks. The taiga is characterized by the presence of many lakes and swamps.
The following ecosystems are represented by broad-leaved forests. Ecosystem species of this type are found in the eastern United States, East Asia, and Western Europe. This is a seasonal climate zone, where the temperature drops below zero in winter, and from 750 to 1500 mm of precipitation falls during the year. The flora of such an ecosystem is represented by such broad-leaved trees as beech and oak, ash and linden. There are bushes and a thick grassy layer here. The fauna is represented by bears and elks, foxes and lynxes, squirrels and shrews. Owls and woodpeckers, thrushes and falcons live in such an ecosystem.
The steppe temperate zones are found in Eurasia and North America. Their counterparts are Tussoks in New Zealand, as well as pampas in South America. The climate in these areas is seasonal. In summer, the air heats up from moderately warm to very high values. Winter temperatures are negative. During the year there is from 250 to 750 millimeters of precipitation. The flora of the steppes is represented mainly by turf grasses. Among the animals there are bison and antelopes, saigas and ground squirrels, rabbits and marmots, wolves and hyenas.
Chaparrals are located in the Mediterranean, as well as in California, Georgia, Mexico and on the southern coast of Australia. These are zones of mild temperate climate, where from 500 to 700 millimeters of precipitation falls during the year. From the vegetation there are shrubs and trees with evergreen hard leaves, such as wild pistachio, laurel, etc.
Ecological systems such as savannahs are located in East and Central Africa, South America and Australia. Most of them are in South India. These are zones of hot and dry climate, where from 250 to 750 mm of precipitation falls during the year. The vegetation is mainly grassy, only in some places there are rare deciduous trees (palms, baobabs and acacias). The animal world is represented by zebras and antelopes, rhinos and giraffes, leopards and lions, vultures, etc. There are many blood-sucking insects in these parts, such as tsetse flies.
Deserts are found in some areas of Africa, in northern Mexico, etc. The climate is dry, with less than 250 mm of precipitation per year. Days in deserts are hot and nights are cold. The vegetation is represented by cacti and sparse shrubs with extensive root systems. Ground squirrels and jerboas, antelopes and wolves are common among representatives of the animal world. This is a fragile ecosystem, easily destroyed by water and wind erosion.
Semi-evergreen tropical deciduous forests are found in Central America and Asia. In these zones, there is a change of dry and wet seasons. The average annual rainfall is from 800 to 1300 mm. Tropical forests are inhabited by rich wildlife.
Rainforest tropical evergreen forests are found in many parts of our planet. There are they in Central America, in the north of South America, in the central and western parts of equatorial Africa, in the coastal regions of northwestern Australia, as well as on the islands of the Pacific and Indian oceans. Warm climatic conditions in these parts do not differ seasonally. Heavy rainfall exceeds the limit of 2500 mm throughout the year. This system is distinguished by a huge variety of flora and fauna.
Existing natural complexes, as a rule, do not have any clear boundaries. There must be a transition zone between them. In it, not only the interaction of populations of different types of ecosystems takes place, but also special types of living organisms are found. Thus, the transition zone includes a greater variety of representatives of fauna and flora than the territories adjacent to it.
Water natural complexes
These units of the biosphere can exist in fresh water bodies and seas. The first of these include such ecosystems as:
Lentic are reservoirs, that is, stagnant waters;
Lotic, represented by streams, rivers, springs;
Upwelling areas where productive fishing takes place;
Straits, bays, estuaries, which are estuaries;
Deep water reef zones.
An example of a natural complex
Ecologists distinguish a wide variety of types of natural ecosystems. Nevertheless, the existence of each of them occurs according to the same pattern. In order to most deeply understand the interaction of all living and non-living beings in a unit of the biosphere, consider the species All microorganisms and animals living here have a direct impact on the chemical composition of air and soil.
The meadow is a balanced system that includes various elements. Some of them are macro-producers, which are herbaceous vegetation, create organic products of this terrestrial community. Further, the life of the natural complex is carried out at the expense of the biological food chain. Plant animals or primary consumers feed on meadow grasses and their parts. These are such representatives of the fauna as large herbivores and insects, rodents and many species of invertebrates (gopher and hare, partridge, etc.).
Primary consumers are eaten by secondary ones, which include carnivorous birds and mammals (wolf, owl, hawk, fox, etc.). Further reducers are connected to work. Without them, a complete description of the ecosystem is impossible. Species of many fungi and bacteria are these elements in the natural complex. Reducers decompose organic products to a mineral state. If the temperature conditions are favorable, then plant remains and dead animals quickly break down into simple compounds. Some of these components contain batteries that are leached out and reused. The more stable part of organic residues (humus, cellulose, etc.) decomposes more slowly, nourishing the plant world.
Anthropogenic ecosystems
The natural complexes considered above are able to exist without any human intervention. The situation is quite different in anthropogenic ecosystems. Their connections work only with the direct participation of a person. For example, the agroecosystem. The main condition for its existence is not only the use of solar energy, but also the receipt of "subsidies" in the form of a kind of fuel.
In part, this system is similar to the natural one. Similarity with the natural complex is observed during the growth and development of plants, which occurs due to the energy of the Sun. However, agriculture is impossible without soil preparation and harvesting. And these processes require the energy subsidies of the human society.
What type of ecosystem does the city belong to? This is an anthropogenic complex, in which fuel energy is of great importance. Its consumption compared to the flow of sunlight is two to three times higher. The city can be compared to deep-sea or cave ecosystems. After all, the existence of these particular biogeocenoses largely depends on the supply of substances and energy from the outside.
Urban ecosystems have emerged as a result of a historical process called urbanization. Under his influence, the population of countries left the countryside, creating large settlements. Gradually, cities increasingly strengthened their role in the development of society. At the same time, to improve life, man himself created a complex urban system. This led to some detachment of cities from nature and disruption of existing natural complexes. The settlement system can be called urbanistic. However, as the industry developed, things changed somewhat. What type of ecosystems does the city in which the plant or factory operates belong to? Rather, it can be called industrial-urban. This complex consists of residential areas and territories on which facilities are located that produce a variety of products. The ecosystem of the city differs from the natural one in a more abundant and, moreover, toxic stream of various wastes.
In order to improve their environment, people create so-called green belts around their settlements. They consist of grassy lawns and shrubs, trees and ponds. These small natural ecosystems create organic products that do not play a special role in urban life. For existence, people need food, fuel, water and electricity from outside.
The process of urbanization has significantly changed the life of our planet. The impact of the artificially created anthropogenic system has changed nature to a large extent in vast areas of the Earth. At the same time, the city affects not only those zones where the architectural and construction objects themselves are located. It affects vast territories and beyond. For example, with an increase in demand for products of the woodworking industry, a person cuts down forests.
During the functioning of the city, many different substances enter the atmosphere. They pollute the air and change climate conditions. Cities have higher cloud cover and less sunshine, more fog and drizzle, and are slightly warmer than nearby rural areas.
