Biological productivity of ecosystems. Productivity primary

The ability of living organisms to create new biomass is called productivity . The rate of biomass formation per unit time per unit area is called products . Biological products are expressed in joules per 1 m 2 per day, calories per 1 m 2 per day, kilograms per 1 ha per one year.

The organic mass created by a plant per unit of time is called primary production . Gross primary production called the total amount of matter and energy produced by the autotrophs of the ecosystem. Net primary production -accumulation rate organic matter in plant tissues after subtracting the cost of respiration. Consumers can only use pure primary products.

secondary production in ecosystems it is formed by consumers. The secondary production of the community is always less than the primary production. According to the pyramid of biological production at each previous trophic level, the amount of biomass created per unit of time is greater than at the next one.

6.4. Homeostasis and Ecosystem Dynamics

The stability and balance of the processes occurring in ecosystems allows us to state that they are generally characterized by a state homeostasis , like their constituent populations and every living organism. The instability of the habitat in ecosystems is compensated by biocenotic adaptive mechanisms.

The main reason for the instability of ecosystems is: the imbalance of the circulation of substances. The loss of the main mass species from the composition of the biocenosis leads to: the destruction of the biocenosis, the change of the biocenosis.

Environmental duplication rule: a disappearing or destroyed species of a living being within one level of the ecological pyramid replaces another functionally-biocenotically similar one. The most stable are ecosystems in which there is a large species diversity; the presence of non-specialized species; relative isolation from neighboring ecosystems; large biomass; a large number of supply chains.

Ecosystem parameters, like all biological objects, experience periodic cyclic changes: daily and seasonal fluctuations. fluctuations- short-term reversible changes in ecosystems with a cycle of less than 10 years. Characteristically, with such dynamics, the fundamental properties of the ecosystem, including integrity and functional stability, are preserved.

During successions, the functional properties of ecosystems change in a certain direction. succession called sequential in time directed change of some communities by others in a certain area of ​​the environment.

The reason for the start of succession is changes in the fundamental properties of the habitat: volcanic eruptions, fires, clearing of forest land, plowing of steppe areas, open pit mining minerals, creation of ponds and reservoirs.

succession series- a chain of biocenoses replacing each other. Succession processes take a certain period of time. Most often, these are years and tens of years, but there are also very rapid changes in communities, for example, in temporary reservoirs, and very slow, secular changes in ecosystems associated with evolution on Earth.

In the successional series, immature (intermediate) and mature communities are distinguished. Immature communities characterized by: instability; a limited number of species; simple food chains; excess plant production. Mature communities are characterized by: stability; species diversity; complex food chains; an increase in total biomass and production. Mature communities are the most adapted in relation to the complex of existing climatic conditions this locality.

According to the general nature of successions are divided into primary and secondary. primary succession starts at rock devoid of soil; surfaces where there were no autotrophs before (fouling of a bare rock with lichens, settlement of cereals on mountain dunes). Secondary successions develop on a substrate originally modified by the activity of a complex of living organisms that existed on this place earlier - before a fire, flood, clearing, etc. (turning a lake into a swamp, turning a swamp into a wet meadow, changing a meadow into a forest, changing a birch forest into an oak forest, developing a forest on an abandoned field).

Questions for self-control

1) Which concept is broader, biogeocenosis or ecosystem?

The ability of living organisms to create new biomass is called productivity. The rate of biomass formation per unit time per unit area is called products. Biological products are expressed in joules per 1 m 2 per day, calories per 1 m 2 per day, kilograms per 1 ha per one year.

The organic mass created by a plant per unit of time is called primary products. Gross primary production is the total amount of matter and energy produced by the autotrophs of an ecosystem. Net primary production – the rate of accumulation of organic matter in plant tissues after subtracting the cost of respiration. Consumers can only use pure primary products.

Secondary products in ecosystems are formed by consumers. The secondary production of the community is always less than the primary production. According to the pyramid of biological production at each previous trophic level, the amount of biomass created per unit of time is greater than at the next one.

The amount of energy supplied per year to a certain area depends on the latitude of this area and on the cloud cover, i.e. from factors that promote photosynthesis. The average productivity of land areas corresponds to the assimilation of approximately 0.3% of the light energy reaching the Earth's surface.

Four groups of areas have been identified that differ in the primary productivity of ecosystems:

1) open seas and deserts (productivity is usually less than 500-1000 kcal / m 2 per year;

2) herbaceous semi-arid formations, some agrocenoses, deep lakes, alpine forests, maritime littoral (500-3000 kcal/m 2 per year;

3) moist forests, shallow lakes, pastures and most agrocenoses (300-10000 kcal/m 2 per year);

4) some estuaries, coral reefs (more than 10,000 kcal/m2 per year).

The quality of food and the distribution of energy to perform the various functions of organisms determines the nature of the flow of energy through the community. The strongest differences in this regard exist between aquatic and terrestrial ecosystems. Productivity reaches its highest level in those places where there is an abundance of light, heat, water and mineral nutrients.

Humidity and temperature are usually the first important factors limiting the productivity of terrestrial systems, and mineral elements are the second. The availability of moisture to compensate for such losses is the main determinant of land productivity. There is an almost linear relationship between precipitation and net primary production, increasing with the increase in mean annual precipitation. In temperate and arctic ecosystems, low winter temperatures and long nights reduce productivity. The ecosystems of swamps and marshes are on the verge between terrestrial and aquatic habitats, and in terms of plant productivity they correspond to tropical forests. Plants that live on marches are highly productive, since their roots are constantly under water, and their leaves are in the light and in the air. In addition, they are abundantly supplied with nutrients, because the detritus washed into the marches is quickly decomposed by bacteria.

In aquatic ecosystems, energy is quickly and very efficiently transferred from one trophic level to another, which creates the opportunity for the formation of long food chains. The main factor limiting the productivity of aquatic ecosystems is a small amount of mineral nutrients. This limits productivity by almost one order of magnitude compared to the productivity of temperate forests. Phosphorus is one of the most deficient elements of mineral nutrition in waters. open ocean.

In the zones of upwelling (where nutrients are carried to the surface from the depths of the sea by vertical currents) and the continental shelf (where there is an active exchange between bottom sediments and surface waters) production is higher, averaging 500 and 360 g/m 2 per year, respectively. The production of shallow estuaries, coral reefs, and coastal kelp beds approaches that of neighboring terrestrial habitats. ecosystems fresh water have a wide range of products. Productivity is highest at the land-water interface: in certain wet or aquatic terrestrial communities and in some coastal and shallow water communities of aquatic ecosystems.

Primary and secondary production. One of the most important properties of ecosystems is the ability to create organic matter, which is called products. Ecosystem productivity- this is the rate of production formation per unit of time (hour, day, year) per unit area (square meter, hectare) or volume (in aquatic ecosystems). The organic mass created by producers per unit of time is called primary products communities. It is subdivided into gross and clean products. Gross primary production is the amount of organic matter created by plants per unit of time at a given rate of photosynthesis. Part of this production is used to maintain the life of the plants themselves (spending on respiration). In temperate and tropical forests, plants spend from 40 to 70% of gross production on respiration. The rest of the created organic mass characterizes net primary production, which represents the growth rate of plants. Being processed in food chains, it goes to replenish the mass of heterotrophic organisms.

secondary production is the increase in the mass of consumers per unit of time. It is calculated separately for each trophic level. Consumers live off the net primary production of the community. In different ecosystems, they spend it with different completeness. If the rate of withdrawal of primary production in food chains lags behind the growth rate of plants, then this leads to a gradual increase in the biomass of producers. Biomass is the total mass of organisms of a given group or the entire community as a whole. In stable communities with a balanced cycle of substances, all products are spent in food chains and biomass remains constant.

The production and biomass of ecosystems is not only a resource used for food, the environment-forming and environment-stabilizing role of ecosystems is directly dependent on these indicators: the intensity of carbon dioxide absorption and oxygen release by plants, regulation of the water balance of territories, noise suppression, etc. Biomass, including dead organic matter, is the main reservoir of carbon concentrations on land. The theoretically predicted rate of creation of primary biological products is determined by the capabilities of the photosynthetic apparatus of plants. It is known that only 44% solar radiation refer to photosynthetically active radiation (PAR) - at a wavelength suitable for photosynthesis. The maximum efficiency of photosynthesis achieved in nature is 10–12% of the PAR energy, which is about half of the theoretically possible. It is celebrated in the most favorable conditions. In general, for the globe the assimilation of solar energy by plants does not exceed 0.1%, since the photosynthetic activity of plants is limited by many factors: lack of heat and moisture, unfavorable soil conditions, etc. Vegetation productivity changes not only in the transition from one climate zone to another, but also within each zone (Table 2.) On the territory of Russia in zones of sufficient moisture, primary productivity increases from north to south, with an increase in heat inflow and the duration of the growing season. The annual growth of vegetation varies from 20 c/ha on the coast of the Northern Arctic Ocean up to 200 c/ha for Black Sea coast Caucasus. The largest increase in plant mass reaches an average of 25 g/m 2 per day under very favorable conditions, with a high supply of plants with water, light and minerals. On the large areas plant productivity does not exceed 0.1 g / m 2: in hot and polar deserts and vast interior spaces oceans with extreme nutritional deficiencies for algae.

table 2

Biomass and primary productivity of the main types of ecosystems

(according to T.A. Akimova, V.V. Khaskin, 1994)

For the five continents of the world, the average productivity of ecosystems differs relatively little (82–103 c/ha per year). The exception is South America(209 c/ha per year), in most of which the conditions for the life of vegetation are very favorable.

The total annual production of dry organic matter on Earth is 150–200 billion tons. More than a third of it is formed in the oceans, about two thirds - on land.

Almost all of the net primary production of the Earth serves to sustain the life of all heterotrophic organisms. Human nutrition is provided mainly by agricultural crops, which occupy approximately 10% of the land area. Agricultural areas, with their rational use and distribution of products, could provide plant food for approximately twice the population of the planet than the current one. It is more difficult to provide the population with secondary products. The resources available on Earth, including livestock products and the results of fisheries on land and in the ocean, can provide annually less than 50% of the needs of the modern population of the Earth. Consequently, most of the world's population is in a state of chronic protein starvation. In this regard, increasing the biological productivity of ecosystems and especially secondary products is one of the most important tasks of mankind.

ecological pyramids. Each ecosystem has a specific trophic structure, which can be expressed either by the number of individuals at each trophic level, or by their biomass, or by the amount of energy fixed per unit area per unit of time at each subsequent trophic level. Graphically, this is usually represented as a pyramid, the base of which is the first trophic level, and the subsequent ones form the floors and top of the pyramid.

Rice. 17. Simplified diagram of the pyramid of numbers (according to G.A. Novikov, 1979)

There are three main types of ecological pyramids - numbers, biomass and production (or energy).

Pyramid of numbers reflects the distribution of individuals by trophic levels. It has been established that in trophic chains, where energy transfer occurs mainly through predator-prey connections, the following rule is often observed: total number individuals in food chains at each subsequent trophic level decreases(Fig. 17).

This is explained by the fact that predators, as a rule, are larger than their victims, and one predator needs several victims to maintain its life. For example, one lion needs 50 zebras per year. However, there are exceptions to this rule. Wolves, hunting together, can kill a prey larger than themselves (for example, deer). Spiders and snakes, possessing poison, kill large animals.

biomass pyramid reflects the total mass of organisms of each trophic level. In most terrestrial ecosystems, the total mass of plants is greater than the biomass of all herbivorous organisms, and the mass of the latter, in turn, exceeds the mass of all predators (Fig. 18)

			Z F

Coral reef Pelagial deposit

Rice. 18. Pyramids of biomass in some biocenoses (according to F. Dre, 1976):

P - producers, RK - plant consumers, PC - carnivorous consumers, P - phytoplankton, Z - zooplankton

In oceans and seas, where unicellular algae are the main producers, the biomass pyramid has an inverted appearance. Here, all net primary production is quickly involved in food chains, the accumulation of algae biomass is very small, and their consumers are much larger and have a long lifespan, so the trend towards biomass accumulation prevails at higher trophic levels.

Pyramid of products (energy) gives the most complete picture of the functional organization of the community, as it reflects the laws of energy expenditure in food chains: the amount of energy contained in organisms at each subsequent trophic level of the food chain is less than at the previous level.

Rice. 19. Product pyramid

The amount of production formed per unit of time at different trophic levels obeys the same rule that is characteristic of energy: at each subsequent level of the food chain, the amount of products created per unit of time is less than at the previous one. This rule is universal and applies to all types of ecosystems (Fig. 19). Pyramids of energy are never inverted.

The study of the laws of ecosystem productivity, the ability to quantify the flow of energy are extremely important in practical terms, since the primary production of agrocenoses and natural communities exploited by man is the main source of food for mankind. No less important is the secondary products that are obtained from farm animals. Accurate calculations of the energy flow on the scale of the productivity of ecosystems make it possible to regulate the cycle of substances in them in such a way as to achieve maximum output products beneficial to humans. Finally, it is very important to have a good understanding of the allowable limits for the removal of plant and animal biomass from natural systems so as not to undermine their productivity.

Primary and secondary production

The rate at which ecosystem producers fix solar energy in the chemical bonds of synthesized organic matter determines the productivity of communities. The organic mass created by plants per unit of time is called primary products communities. Production is expressed quantitatively in wet or dry mass of plants or in energy units - the equivalent number of joules.

Gross primary production- the amount of substance created by plants per unit of time at a given rate of photosynthesis. Part of this production is used to maintain the life of the plants themselves (spending on respiration). This part can be quite large. In tropical forests and mature forests of the temperate zone, it is from 40 to 70% of gross production. Planktonic algae use about 40% of the recorded energy for metabolism. The same order of spending on breathing in most crops. The rest of the created organic mass characterizes pure primary production, which is the growth rate of plants. Net primary production is an energy reserve for consumers and decomposers. Being processed in food chains, it goes to replenish the mass of heterotrophic organisms. The increase in the mass of consumers per unit time is secondary production communities. Secondary production is calculated separately for each trophic level, since the mass gain at each of them occurs due to the energy coming from the previous one.

Heterotrophs, being included in the trophic chains, ultimately live at the expense of the net primary production of the community. In different ecosystems, they spend it with different completeness. If the rate of withdrawal of primary production in food chains lags behind the growth rate of plants, then this leads to a gradual increase in the total biomass of producers. Under biomass understand the total mass of organisms of a given group or the entire community as a whole. Biomass is often expressed in equivalent energy units.

Insufficient disposal of litter products in decomposition chains results in the accumulation of dead organic matter in the system, which occurs, for example, when swamps become peaty, overgrowing shallow water bodies, creating large stocks of litter in taiga forests, etc. The biomass of a community with a balanced cycle of substances remains relatively constant , since almost all primary production is spent in food chains and decomposition.

pyramid rule

Ecosystems are very diverse relative speed creation and expenditure of both primary production and secondary production at each trophic level. However, all ecosystems, without exception, are characterized by certain quantitative ratios of primary and secondary production, which are called product pyramid rules: at each previous trophic level, the amount of biomass created per unit of time is greater than at the next. Graphically, this rule is expressed in the form of pyramids, tapering upwards and formed by stacked rectangles of equal height, the length of which corresponds to the scale of production at the corresponding trophic levels. The product pyramid reflects the laws of energy expenditure in food chains.

The rate of creation of organic matter does not determine its total reserves, i.e., the total biomass of all organisms of each trophic level. The available biomass of producers or consumers in specific ecosystems depends on how the rates of accumulation of organic matter at a certain trophic level and its transfer to a higher level correlate, i.e., how much the formed reserves are consumed. An important role is played by the turnover rate of the generations of the main producers and consumers.

Rice. 150. Pyramids of biomass in some biocenoses (according to F. Dre, 1976): P - producers; RK - herbivorous consumers; PC - carnivorous consumers; F, phytoplankton; 3 - zooplankton

In most terrestrial ecosystems, there is also biomass pyramid rule, i.e., the total mass of plants turns out to be greater than the biomass of all phytophages and herbivores, and the mass of those, in turn, exceeds the mass of all predators (Fig. 150). The ratio of annual vegetation growth to biomass in terrestrial ecosystems is relatively small. In different phytocenoses, where the main producers differ in duration life cycle, size and growth rate, this ratio varies from 2 to 76%. The rates of relative growth of biomass are especially low in forests of different zones, where annual production is only 2–6% of the total mass of plants accumulated in the bodies of long-lived large trees. Even in the most productive tropical rainforests, this value does not exceed 6.5%. In communities dominated by herbaceous forms, the rate of biomass reproduction is much higher: the annual production in the steppes is 41–55%, and in herbal tugai and ephemeral-shrub semi-deserts it even reaches 70–76%.

The ratio of primary production to plant biomass determines the extent of plant mass grazing that is possible in a community without undermining its productivity. The relative share of primary production consumed by animals in herbaceous communities is higher than in forests. Ungulates, rodents, phytophagous insects in the steppes use up to 70% of the annual growth of plants, while in forests, on average, no more than 10%. However, the possible limits of alienation of plant mass by animals in terrestrial communities are not fully realized, and a significant part of the annual production goes to waste.

In the pelagial of the oceans, where the main producers are unicellular algae with a high turnover rate of generations, their annual production can exceed the biomass reserve by tens and even hundreds of times (Fig. 151). All pure primary production is so quickly involved in the food chain that the accumulation of algae biomass is very small, but due to the high reproduction rates, a small supply of them is sufficient to maintain the rate of organic matter reproduction.

Rice. 151. Scheme of the ratio of production and biomass in bacteria (1), phytoplankton (2), zooplankton (3), benthos (4) and fish (5) in the Barents Sea (according to L. A. Zenkevich from S. A. Zernov, 1949)

For the ocean, the biomass pyramid rule is invalid (the pyramid is inverted). At the highest trophic levels, the tendency to accumulate biomass prevails, since the life span of large predators is long, the turnover rate of their generations, on the contrary, is low, and a significant part of the substance that enters the food chains is retained in their bodies.

All three rules of the pyramids - production, biomass and numbers - ultimately express energy relations in ecosystems, and if the last two are manifested in communities with a certain trophic structure, then the first (production pyramid) has a universal character.

Knowledge of the laws of ecosystem productivity, the ability to quantify the flow of energy are of extreme practical importance. The primary production of agrocenoses and human exploitation of natural communities is the main source of food for mankind. No less important is the secondary products obtained from agricultural and game animals, since animal proteins include a number of amino acids essential for humans, which are not found in plant foods. Accurate calculations The flow of energy and the scale of productivity of ecosystems make it possible to regulate the cycle of substances in them in such a way as to achieve the greatest yield of products beneficial to humans. In addition, it is necessary to have a good understanding of the allowable limits for the removal of plant and animal biomass from natural systems in order not to undermine their productivity. Such calculations are usually very complicated due to methodological difficulties and are most accurately performed for simpler aquatic ecosystems. An example of energy ratios in a particular community can be the data obtained for the ecosystems of one of the lakes (Table 2). The P/B ratio reflects the growth rate.

table 2

Energy flow in the ecosystem of a eutrophic lake (in kJ / m 2) on average for the growing season (according to G. G. Vinberg, 1969)

In this aquatic community, the biomass pyramid rule applies, since total weight producers are higher than phytophages, and the proportion of predators, on the contrary, is less. The highest productivity is typical for phyto- and bacterioplankton. In the studied lake, their P/B ratios are quite low, which indicates a relatively weak involvement of primary production in food chains. The biomass of benthos, which is based on large molluscs, is almost twice that of plankton, while the production is many times lower. In zooplankton, the production of non-predatory species is only slightly higher than the diet of their consumers, therefore, food connections plankton are quite tense. The entire production of non-predatory fish is only about 0.5% of the primary production of the reservoir, and, therefore, fish occupy a modest place in the energy flow in the lake ecosystem. However, they consume a significant part of the zooplankton and benthos growth and therefore have a significant influence on the regulation of their production.

The description of the energy flow, therefore, is the foundation of a detailed biological analysis to establish the dependence of final products useful to humans on the functioning of the entire ecological system as a whole.

As mankind, with a stubbornness worthy best use, turns the face of the Earth into a continuous anthropogenic landscape, the assessment of the productivity of various ecosystems is becoming increasingly practical. Man has learned to obtain energy for his industrial and domestic needs by the most different ways, but it can receive energy for its own nutrition only through photosynthesis.

In the human food chain, producers almost always turn out to be at the base, converting biomass of organic matter into energy. For this is precisely the energy that consumers and, in particular, humans can subsequently use. At the same time, the same producers produce the oxygen necessary for breathing and absorb carbon dioxide, and the rate of gas exchange of producers is directly proportional to their bioproductivity. Therefore, in a generalized form, the question of the efficiency of ecosystems is formulated simply: what energy can vegetation store in the form of biomass of organic matter? On the top fig. 1 shows the values ​​​​of specific (per 1 m 2) productivity of the main types. This diagram shows that human-made agricultural land is by no means the most productive ecosystem. Marshy ecosystems provide the highest specific productivity - humid tropical jungles, estuaries and estuaries of rivers and ordinary swamps of temperate latitudes. At first glance, they produce biomass that is useless to humans, but it is these ecosystems that purify the air and stabilize the composition of the atmosphere, purify water and serve as reservoirs for rivers and groundwater, and, finally, are breeding grounds for a huge number of fish and other inhabitants of the waters used in human food. Occupying 10% of the land area, they create 40% of the biomass produced on land. And this without any human effort! That is why the destruction and "cultivation" of these ecosystems is not only "killing the goose that lays the golden eggs", but may also be suicidal for humanity. Referring to the bottom diagram in Fig. 1, it can be seen that the contribution of deserts and dry steppes to the productivity of the biosphere is negligible, although they already occupy about a quarter of the land surface and, due to anthropogenic interference, tend to rapid growth. In the long term, the fight against desertification and soil erosion, that is, the transformation of unproductive ecosystems into productive ones, is a reasonable way for anthropogenic changes in the biosphere.

The specific bioproductivity of the open ocean is almost as low as that of semi-deserts, and its enormous total productivity is explained by the fact that it occupies more than 50% of the Earth's surface, twice the entire land area. Attempts to use the open ocean as a serious source of food in the near future can hardly be economically justified precisely because of its low specific productivity. However, the role of the open ocean in stabilizing the conditions of life on Earth is so great that its protection from pollution, especially by oil products, is absolutely necessary.

Rice. 1. Bioproductivity of ecosystems as energy accumulated by producers in the process of photosynthesis. World electricity production is about 10 Ecal / year, and the whole of humanity consumes 50-100 Ecal / year; 1 Ecal (exacalorie) \u003d 1 million billion kcal \u003d K) 18 cal

The contribution of temperate and taiga forests to the viability of the biosphere cannot be underestimated. Their relative resistance to anthropogenic influences is especially significant in comparison with the humid tropical jungles.

The fact that the specific productivity of agricultural land is still on average much lower than that of many natural ecosystems shows that the possibilities for increasing food production on existing areas are far from being exhausted. An example is paddy rice plantations, in essence, anthropogenic swamp ecosystems, with their huge yields obtained with modern agricultural technology.

Biological productivity of ecosystems

The rate at which ecosystem producers fix solar energy in the chemical bonds of synthesized organic matter determines the productivity of communities. The organic mass created by plants per unit of time is called primary products communities. Production is expressed quantitatively in raw or dry mass of plants or in energy units - the equivalent number of joules.

Gross primary production- the amount of substance created by plants per unit of time at a given rate of photosynthesis. Part of this production is used to maintain the life of the plants themselves (spending on respiration).

The rest of the created organic mass characterizes net primary production, which represents the growth rate of plants. Net primary production is an energy reserve for consumers and decomposers. Being processed in food chains, it goes to replenish the mass of heterotrophic organisms. The increase per unit time of the mass of consumers - secondary production communities. Secondary production is calculated separately for each trophic level, since the mass gain at each of them occurs due to the energy coming from the previous one.

Heterotrophs, being included in the trophic chains, live at the expense of the net primary production of the community. In different ecosystems, they spend it with different completeness. If the rate of withdrawal of primary production in food chains lags behind the growth rate of plants, then this leads to a gradual increase in the total biomass of producers. under biomass understand the total mass of organisms of a given group or the entire community as a whole. Insufficient disposal of litter products in decomposition chains results in the accumulation of dead organic matter in the system, which occurs, for example, when swamps become peaty, overgrowth of shallow water bodies, the creation of large stocks of litter in taiga forests, etc. The biomass of a community with a balanced cycle of substances remains relatively constant, since almost all primary production is spent in the food and decay chains.

Ecosystems also differ in the relative rate of creation and consumption of both primary and secondary products at each trophic level. However, all ecosystems, without exception, are characterized by certain quantitative ratios of primary and secondary production, which are called right-handed product pyramid: at each previous trophic level, the amount of biomass created per unit of time is greater than at the next. Graphically, this rule is usually illustrated in the form of pyramids, tapering upwards and formed by stacked rectangles of equal height, the length of which corresponds to the scale of production at the corresponding trophic levels.

The rate of creation of organic matter does not determine its total reserves, i.e. the total biomass of all organisms at each trophic level. The available biomass of producers or consumers in specific ecosystems depends on how the rates of accumulation of organic matter at a certain trophic level and its transfer to a higher one correlate with each other.

The ratio of annual vegetation growth to biomass in terrestrial ecosystems is relatively small. Even in the most productive tropical rainforests, this value does not exceed 6.5%. In communities with a predominance of herbaceous forms, the rate of biomass reproduction is much higher. The ratio of primary production to plant biomass determines the extent of plant mass consumption that is possible in a community without changing its productivity.

For the ocean, the biomass pyramid rule does not apply (the pyramid has an inverted shape).

All three rules of the pyramids - production, biomass and numbers - ultimately reflect energy relations in ecosystems, and if the last two are manifested in communities with a certain trophic structure, then the first (production pyramid) has a universal character. The pyramid of numbers reflects the number of individual organisms (Fig. 2) or, for example, the population by age group.

Rice. 2. Simplified pyramid of the number of individual organisms

Knowledge of the laws of ecosystem productivity and the ability to quantify the flow of energy are of great practical importance. The primary production of agrocenoses and human exploitation of natural communities is the main source of food for mankind.

Accurate calculations of the energy flow and the scale of ecosystem productivity make it possible to regulate the cycle of substances in them in such a way as to achieve the greatest yield of products beneficial to humans. In addition, it is necessary to have a good understanding of the allowable limits for the removal of plant and animal biomass from natural systems in order not to undermine their productivity. Such calculations are usually very complicated due to methodological difficulties.

The most important practical result of the energy approach to the study of ecosystems was the implementation of research on the International Biological Program, conducted by scientists different countries world for a number of years, starting in 1969, in order to study the potential biological productivity of the Earth.

The theoretical possible rate of creation of primary biological products is determined by the capabilities of the photosynthetic apparatus of plants (PAR). The maximum efficiency of photosynthesis achieved in nature is 10-12% of the PAR energy, which is about half of the theoretically possible. A photosynthesis efficiency of 5% is considered very high for a phytocenosis. In general, the assimilation of solar energy by plants does not exceed 0.1% around the globe, since the activity of plant photosynthesis is limited by many factors.

The world distribution of primary biological products is extremely uneven. The total annual production of dry organic matter on Earth is 150-200 billion tons. More than a third of it is formed in the oceans, about two-thirds - on land. Almost all of the net primary production of the Earth serves to sustain the life of all heterotrophic organisms. The energy underused by consumers is stored in their organisms, organic sediments of water bodies, and soil humus.

On the territory of Russia, in zones of sufficient moisture, primary productivity increases from north to south, with an increase in heat inflow and the duration of the growing season. The annual growth of vegetation varies from 20 c/ha on the coast and islands of the Arctic Ocean to more than 200 c/ha on the Black Sea coast of the Caucasus. In the Central Asian deserts, productivity drops to 20 c/ha.

For the five continents of the world, average productivity differs relatively little. The exception is South America, in most of which the conditions for the development of vegetation are very favorable.

Human nutrition is provided mainly by agricultural crops, which occupy approximately 10% of the land area (about 1.4 billion hectares). Total annual growth cultivated plants accounts for about 16% of all land productivity, most of which is accounted for by forests. Approximately half of the crop goes directly to human food, the rest is used for pet food, used in industry and lost in garbage.

The resources available on Earth, including livestock products and the results of fisheries on land and in the ocean, can provide annually less than 50% of the needs of the modern population of the Earth.

Thus, most of the world's population is in a state of chronic protein starvation, and a significant part of people also suffer from general malnutrition.

Productivity of biocenoses

The fixing speed of solar energy determines productivity of biocenoses. The main indicator of production is the biomass of organisms (plants and animals) that make up the biocenosis. There are plant biomass - phytomass, animal biomass - zoomass, bacteriomass and biomass of any specific groups or organisms of individual species.

Biomass - organic matter of organisms, expressed in certain quantitative units and per unit area or volume (for example, g / m 2, g / m 3, kg / ha, t / km 2, etc.).

Productivity is the rate of biomass growth. It is usually referred to a specific period and area, such as a year and a hectare.

It is known that green plants are the first link in food chains and only they are able to independently form organic matter using the energy of the Sun. Therefore, the biomass produced by autotrophic organisms, i.e. the amount of energy converted by plants into organic matter certain area, expressed in certain quantitative units, is called primary products. Its value reflects the productivity of all links of heterotrophic organisms in the ecosystem.

The total production of photosynthesis is called primary gross output. This is all chemical energy in the form of organic matter produced. Part of the energy can be used to support the life (respiration) of the producers of products themselves - plants. If we remove that part of the energy that is spent by plants on respiration, we get net primary production. It can be easily taken into account. It is enough to collect, dry and weigh the plant mass, for example, when harvesting. Thus, net primary production is equal to the difference between the amount of atmospheric carbon taken up by plants during photosynthesis and consumed by them for respiration.

Maximum productivity is typical for tropical equatorial forests. For such a forest, 500 tons of dry matter per 1 ha is not the limit. For Brazil, figures are given at 1500 and even 1700 tons - this is 150-170 kg of plant mass per 1 m 2 (compare: in the tundra - 12 tons, and in broad-leaved forests of the temperate zone - up to 400 tons per 1 ha).

Fertile soil deposits, a high sum of annual temperatures, and an abundance of moisture contribute to maintaining a very high productivity of phytocenoses in the deltas of southern rivers, in lagoons and estuaries. It reaches 20-25 tons per 1 ha per year in dry matter, which significantly exceeds the primary productivity. spruce forests(8-12 tons). Sugarcane manages to accumulate up to 78 tons of phytomass per 1 ha per year. Even a sphagnum bog, under favorable conditions, has a productivity of 8-10 tons, which can be compared with the productivity of a spruce forest.

The "record holders" of productivity on Earth are grass-tree thickets of the valley type, which have been preserved in the deltas of the Mississippi, Parana, Ganges, around Lake Chad and in some other regions. Here, up to 300 tons of organic matter is formed per 1 ha in one year!

secondary production- this is the biomass created by all consumers of the biocenosis per unit of time. When calculating it, calculations are made separately for each trophic level, because when energy moves from one trophic level to another, it grows due to receipt from the previous level. The overall productivity of the biocenosis cannot be assessed by a simple arithmetic sum primary and secondary production, because the increase in secondary production does not occur in parallel with the growth of primary, but due to the destruction of some part of it. There is a withdrawal, a subtraction of secondary production from the total amount of primary production. Therefore, the assessment of the productivity of the biocenosis is carried out according to primary production. Primary production is many times greater than secondary production. In general, secondary productivity ranges from 1 to 10%.

The laws of ecology predetermine differences in the biomass of herbivorous animals and primary predators. Thus, a herd of migrating deer is usually followed by several predators, such as wolves. This allows the wolves to be fed without affecting the reproduction of the herd. If the number of wolves approached the number of deer, then the predators would quickly exterminate the herd and be left without food. For this reason, there is no high concentration of predatory mammals and birds in the temperate zone.