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Ecosystems are different productivity, which, first of all, depends on their geographical position on the surface of the globe. The most productive land biomes are tropical rainforests, and the World Ocean - Coral reefs. It is in these ecosystems that the largest amount of organic matter is produced and transported per unit of time. The high potential of these ecosystems is explained by their proximity to the equator - here the highest solar radiation and constant heat therefore, biochemical reactions in cells are very fast, and photosynthesis is carried out throughout the year.
Biocenoses may differ in their productivity and within the same biome. Multi-tier mature ecosystems, which include a large number of species of organisms occupying a variety of ecological niches, are more productive than single-tier ones with a poor species composition. However, the most productive and species-rich communities are the communities of organisms at the boundaries of two biomes (for example, broad-leaved forest and steppe zones), landscapes (forests and fields), and habitats (marine and freshwater). This is due to the fact that such places are very densely populated. There are both species confined to each type of ecosystems, and organisms that live only in such border areas. Increases in species diversity and productivity in marginal areas are often referred to as the "edge effect", and such areas are ecotones(from Greek. oikos- housing and tonos- voltage). They have a specific structure and are extremely important for the conservation of species and biological diversity (Fig. 138). material from the site
Ecotones- not only the edges of forests, but also floodplains, sea coasts and estuaries - places where fresh river and salt sea water collide. Such desalinated areas are inhabited by marine, anadromous and even freshwater fish. The largest ecotone in Ukraine is the Sea of Azov. It is more correct to call this body of water not the sea, but the huge estuary of the Don. It is no coincidence that the ancient Greeks called it the Meiotian swamp.
Ecosystems are different productivity. The most productive are tropical ecosystems, as well as the boundary communities of organisms in ecotones - transitional zones between different ecosystems, landscapes or habitats.
On this page, material on the topics:
Productive communities biology
The most productive ecosystems and their characteristics
And what are the places where the largest mass of living matter is concentrated
Why are forests more productive ecosystems than steppes?
Which ecosystem is the most productive
Questions about this item:
To assess the importance of a particular species for the circulation of substances in a given biogeocenosis, it is necessary to know not only its biomass, but also the relative rate of its creation, i.e. biological productivity .
In this way,
Biological productivity is the rate of creation of a certain amount of biomass of plants, animals and microorganisms that make up the biogeocenosis.
Biological productivity is determined by the amount of biomass synthesized per unit of time per unit area (or volume) and is most often expressed in grams of carbon or dry organic matter or in energy units - the equivalent number of calories or joules.
Biological productivity can be expressed in terms of production per season, per year, several years, or any other unit of time.
For terrestrial and bottom organisms, biological productivity is determined by the amount of biomass per unit area, and for planktonic and soil organisms - per unit volume.
The key word in the concept of productivity is speed. However, instead of the term "productivity", the term "production" is often used, but the time factor is still taken into account.
Biological productivity cannot be confused with biomass.
Biomass is the amount of living matter of certain organisms, expressed in units of mass (weight) or energy, living in the study area or in the study volume.
For example:
planktonic algae per year per unit area synthesize the same amount of organic matter as highly productive forests, but the biomass of the latter is hundreds of thousands of times greater;
Populations of small mammals, compared with large ones, have a higher growth and reproduction rate and therefore have higher productivity with equal biomass.
Distinguish primary and secondary productivity of ecosystems.
The primary productivity of ecosystems is the rate at which autotrophic organisms (producers) bind solar energy during photosynthesis and store it in the form of chemical bonds of organic substances, i.e. the rate of formation of biomass of organic matter by autotrophs (producers).
Primary productivity is divided into gross and net productivity.
Gross primary productivity is the rate of accumulation of organic matter by producers, including the cost of breathing(i.e. including that part of it that will be consumed in the life processes of plants).
For example, in tropical forests and mature forests of the temperate zone, the cost of respiration is 40-70%, while in planktonic algae and in most crops it is 40%.
Net primary productivity is the rate of accumulation of organic matter in plant tissues minus that part of it that was used for plant respiration.
Therefore, the net primary production accumulated in the form of plant biomass is always less than the gross primary production created by them in the process of photosynthesis.
The net primary productivity of autotrophic organisms (producers) can serve as a source of nutrition for heterotrophic organisms, which form their biomass on its basis.
Secondary productivity is the rate of biomass formation by heterotrophic organisms (consumers).
Secondary productivity is no longer divided into gross and net productivity, since heterotrophs increase their mass due to the primary products created earlier.
Secondary productivity is calculated separately for each trophic level, since the increase in biomass at each of them occurs due to the energy coming from the previous level.
At the same time, it should be taken into account that during the transition from one trophic level of consumers to another, a significant part of the energy is spent in vital processes, so the secondary production of each subsequent trophic level will be less than the production of the previous one.
If in an ecosystem the rate of formation of pure primary production is higher than the rate of its processing by consumers, then this leads to an increase in the biomass of producers.
If at the same time there is insufficient utilization of litter products in the decomposition chains by decomposers, then dead organic matter accumulates (in the form of coal, oil shale, dry leaves, etc.).
In stable ecosystems, biomass remains constant, since almost all created products are consumed in food chains by various consumers and decomposers, i.e. nature tends to use fully the gross output.
However, the equality between the income and consumption of products is a rather rare phenomenon and is observed in the most stable communities, for example, in the tropical zone. However, this creates objective difficulties for the development of agriculture there.
A man, burning a lush tropical forest, hopes to get high yields in the vacated territory. However, it soon turns out that the soils in this area are absolutely barren - all the annual production of the forest growing in this place was consumed by various consumers and decomposers and nothing was deposited in the soils.
In addition to the primary and secondary production of biogeocenoses, there are intermediate and final products.
Intermediates - these are products that, after being consumed by members of the biogeocenosis, again return to the cycle of substances of this system.
end products are products that are removed from the given ecosystem.
For example, products obtained by a person in the process of cultivating crops, breeding domestic animals, hunting, fishing, etc.
The productivity of different ecosystems is not the same and depends on a number of environmental factors, primarily climatic (heat, moisture, etc.).
At the same time, the primary production of organic matter in ecosystems rich in life can exceed the production of relatively poor ecosystems by more than 50 times.
The most productive ecosystems are estuaries and coral reefs (average productivity reaches 20 g/m 2 per day), tropical rain forests and swamps (average productivity is 10 g / m 2 per day).
Highly productive ecosystems are found where climatic conditions are favorable, especially when additional energy is supplied to the ecosystem from outside.
The supply of energy from abiotic components reduces the cost of living organisms to maintain their own life, i.e. they compensate for their breathing costs.
For example, tidal energy increases the productivity of a natural coastal ecosystem by compensating for energy lost through respiration.
Low productivity (0.1-0.5 g/m 2 per day) characterize the ecosystems of deserts and tundras, in which the lack of moisture and heat limits the development of the lower trophic level, as well as the open waters of the seas and oceans, where, with an excess of water, the volume of organic matter is relatively low.
At the same time, it should be noted that most of the globe is covered by oceans and deserts with low productivity, while high productivity is characteristic of relatively small areas of the Earth (estuaries, coral reefs, swamps, rainforests).
The change in the primary productivity of ecosystems in the direction from north to south occurs in the following order:
in terrestrial Arctic biogeocenoses, productivity is low, and the Arctic seas, as well as the Antarctic, are highly productive;
in the tropics, a huge part of the land is occupied by unproductive deserts, the seas of this zone are also poor;
in the equatorial zone, the most highly productive biogeocenoses of coral reefs, estuaries, swamps, and especially tropical rainforests are located.
As we move from north to south, the specific amount of solar energy falling on a unit of the Earth's surface increases, which leads to more species, the accumulation of more significant biomass and an increase in the productivity of terrestrial ecosystems.
In marine ecosystems, the situation is different than on land.
The productivity of the northern seas is high, as well as the seas of the extreme southern latitudes, where cold waters rich in oxygen and nutrients come from the depths. In warm water, oxygen dissolves worse and there are few nutrients (the tropics are rich in species, but relatively unproductive).
The total net primary productivity on Earth is 170 billion tons per year, of which 115 billion tons come from land ecosystems and 55 billion tons from sea ecosystems.
Secondary production (biomass of heterotrophic organisms, primarily animals - zoomass), is many times less than primary production (biomass of plants - phytomass).
In different ecosystems, zoomass makes up an insignificant fraction of biomass (from 0.05% to 5% of the total biomass), however, land animals play an important role in regulating the processes occurring in individual ecosystems and the biosphere as a whole.
It is quite obvious that the life of people, their production activities depend on the productivity of the main biogeocenoses, on primary production and its global distribution.
Human nutrition is provided mainly by crops, which occupy about 10% of the land area and provide approximately 9.1 billion tons of organic matter per year, which is a significant part of the world's resources.
In addition, a huge mass of primary products is used by man as technical raw materials in industry and everyday life (fuel, cotton, flax, essential oil crops, etc.), and about 50% is lost in waste.
But a person consumes not only primary products. It removes from the biosphere a large amount of secondary products in the form of animal food, the costs of which are very difficult to calculate.
Thus, the existing ideas about the productivity of ecosystems and the global distribution of primary production make it possible to navigate the situation that has developed on our planet and, on a strictly scientific basis, develop measures for the rational use of natural resources.
As humanity, with a stubbornness worthy of a better application, turns the face of the Earth into a continuous anthropogenic landscape, the assessment of the productivity of various ecosystems becomes more and more 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 the 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 acceptable 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). The total annual growth of cultivated plants is about 16% of the total productivity of land, 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 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 in a 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 of 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 estimated by a simple arithmetic sum of 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.
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 the primary production of the community. 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 matter created by plants per unit 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 remaining part of the created organic mass characterizes the net primary production, which is the amount of plant growth. 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 of time is a secondary product of the community. 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. Biomass is understood as 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 highly variable in the relative rates of creation and expenditure of both net primary production and net 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 the rules of the production pyramid: at each previous trophic level, the amount of biomass created per unit of time is greater than at the next one. 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 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 level correlate with each other, i.e., how much the formed stocks are consumed. An important role is played by the turnover rate of the generations of the main producers and consumers.
In most terrestrial ecosystems, the biomass pyramid rule also applies, 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. The ratio of annual vegetation growth to biomass in terrestrial ecosystems is relatively small. In different phytocenoses, where the main producers differ in the duration of the life cycle, size and growth rate, this ratio varies from 2 to 76%. The rates of relative growth of biomass are especially low in the forests of different zones, where the 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 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. All pure primary production is so quickly involved in the food chain that the accumulation of algae biomass is very low, but due to the high rates of reproduction, a small supply of them is sufficient to maintain the rate of regeneration of organic matter.
For the ocean, the biomass pyramid rule is invalid, it has an inverted appearance. At the higher 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 pyramid rules - production, biomass and numbers - ultimately express energy relations in ecosystems, and if the first two appear in communities with a certain trophic structure, then the last (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 are the secondary products obtained from agricultural and industrial animals, since animal proteins include a number of amino acids essential for humans, which are not found in plant foods. 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 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.
In this aquatic community, the biomass pyramid rule applies, since the total mass of producers is higher than that of phytophages, while the proportion of predators, on the contrary, is lower. The highest productivity is characteristic of 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, plankton food relations 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.
Distribution of biological products. The most important practical result of the energy approach to the study of ecosystems was the implementation of research under the International Biological Program, carried out by scientists from around the world since 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. The maximum efficiency of photosynthesis achieved in nature is 10-12% of the PAR energy, which is about half of the theoretically possible. Such a speed of energy binding is achieved, for example, in the thickets of dzhugara and reeds in Tajikistan in short-term, most favorable periods. A photosynthesis efficiency of 5% is considered very high for a phytocenosis. In general, the assimilation of solar energy by plants around the globe does not exceed 0.1%, since the photosynthetic activity of plants is limited by many factors.
The world distribution of primary biological products is extremely uneven. The largest absolute increase in plant mass reaches an average of 25 g per day in very favorable conditions, for example, in river estuaries and in. estuaries of arid regions, with a high supply of plants with water, light and mineral nutrition. On large areas, the productivity of autotrophs does not exceed 0.1 g/m. Such are the hot deserts where life is limited by a lack of water, the polar deserts where there is not enough heat, and the vast interior spaces of the oceans with extreme scarcity. nutrients. The total annual production of dry organic matter on Earth is 150-200 billion tons. About 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. Energy, underused by consumers, is stored in their bodies, organic sediments of water bodies and soil humus. .
The efficiency of solar radiation binding by vegetation decreases with a lack of heat and moisture, with unfavorable physical and chemical properties soil, etc. The productivity of vegetation changes not only during the transition from one climatic zone to another, but also within each zone. On the territory of the USSR, in zones of sufficient moisture, primary productivity increases from north to south, with an increase in the influx of heat 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.
The average PAR energy utilization factor for the entire territory of the USSR is 0.8%: from 1.8-2.0% in the Caucasus to 0.1-0.2% in the deserts of Central Asia. In most of the eastern regions of the country, where moistening conditions are less favorable, this coefficient is 0.4-0.8%, in the European territory - 1.0-1.2%. The efficiency of total radiation is about half as low.
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 (Table 3).
Human nutrition is provided mainly by agricultural crops, which occupy approximately 10% of the land area (about 1.4 billion hectares). The total annual growth of cultivated plants is about 16% of the total land productivity, most of which falls on forests.
Approximately half of the crop goes directly to human nutrition, the rest is used for pet food, used in industry and lost in garbage. In total, a person consumes about 0.2% of the primary production of the Earth.
Plant food is energetically cheaper for people than animal food. Agricultural areas at rational use and distribution of products could provide plant food for about twice the population of the Earth than the current one. However, agricultural production requires a lot of labor and investment. It is especially difficult to provide the population with secondary products. The human diet should include at least 30 g of protein per day. The resources available on Earth, including livestock products and the results of fisheries on land and in the ocean, can annually provide only about 50% of the needs of the modern population of the Earth.
The existing limitations imposed by the scale of secondary productivity are exacerbated by the imperfection social systems distribution. A large part of the world's population is thus in a state of chronic protein starvation, and a significant part of people also suffer from general malnutrition.
Thus, increasing the biological productivity of ecosystems and especially secondary products is one of the main tasks facing humanity.
The amount of radiant energy converted by autotrophic organisms, i.e., mainly chlorophyll-bearing plants, into chemical energy is called primary productivity of biocenosis.
There are productivity: gross, covering all chemical energy in the form of produced organic matter, including that part of it that is oxidized during respiration and spent on maintaining the vital activity of plants, and net, corresponding to the increase in organic matter in plants.
Net productivity is theoretically defined very in a simple way. To do this, they collect, dry and weigh the plant mass that has grown over a certain time. Of course, this method only gives good results if it is applied to the plants from the moment they are sown until they are harvested. Net productivity can also be determined using hermetic vessels, measuring, on the one hand, the amount of carbon dioxide absorbed per unit time or oxygen released in the light, on the other hand, in the dark, where the assimilation activity of chlorophyll stops. In this case, the amount of oxygen absorbed per unit time and the amount of carbon dioxide released are measured, and thus the magnitude of gas exchange is estimated. By adding the obtained values to the net productivity, the gross productivity is obtained. You can also use the method of radioactive tracers or the determination of the amount of chlorophyll per unit area of leaf surface. The principle of these techniques is simple, but their application in practice often requires great care in operations, without which it is impossible to obtain accurate results.
Some data on individual biocenoses obtained by these methods are given. IN this case it was possible to simultaneously measure both gross and net productivity. In natural ecosystems (the first two), respiration reduces productivity by more than half. In the experimental field of alfalfa, the respiration of young plants during the period of intensive vegetation takes little energy; adult plants that have finished growing consume almost as much energy as they produce. As the plant ages, the proportion of energy lost increases. Thus, the maximum productivity of plants during the growth period should be considered as a general pattern.
It was possible to determine the primary gross productivity by measuring gas exchange in a number of aquatic natural biocenoses.
Along with the data already mentioned for Silver Springs, the highest productivity was found in coral reefs. It is formed due to zoochlorella - symbionts of polyps and especially filamentous algae that live in the voids of calcareous skeletons, the total mass of which is approximately three times the mass of polyps. Biocenoses with even higher productivity were found in sewage PCS. Indiana in the USA, but only for a very short time and during the most favorable season of the year.
It is these data that people are most interested in. Analyzing them, it should be noted that the productivity of the best agricultural crops does not exceed the productivity of plants in natural habitats; their harvest is comparable to that of plants growing in biocenoses similar in climate. These crops often grow faster, but their vegetation is generally seasonal. For this reason, they use less solar energy than ecosystems that function throughout the year. For the same reason, an evergreen forest is more productive than a deciduous forest.
Habitats with a productivity of more than 20 g/(m 2 day) should be considered an exception. Interesting data has been obtained. Despite the fact that the limiting factors in different environments are different, there is not much difference between the productivity of terrestrial and aquatic ecosystems. In low latitudes, deserts and the open sea are the least productive. This is a real biological vacuum, occupying the largest space. At the same time, next to them are biocenoses with the highest productivity - coral reefs, estuaries, tropical forests. But they occupy only a limited area. It should also be noted that their productivity is the result of a very complex balance that has developed over a long evolutionary period, to which they owe their exceptional efficiency. The uprooting of virgin forests and their replacement by agricultural land lead to a very significant decrease in primary productivity. Apparently, swampy areas should be preserved because of their high productivity.
In the north and south polar regions, land productivity is very low, as solar energy is only effective for a few months of the year; on the contrary, due to the low temperature of the water, marine communities, of course, at shallow depths, are among the richest habitats in the world with living matter. There is a lot of space in the middle latitudes, they occupy unproductive steppes, but at the same time quite extensive areas are covered with forests. It is in these areas that agricultural crops give the best yields. This is a zone with relatively high average productivity.
Based on the data presented, various authors have tried to estimate the primary productivity of the entire globe. Solar energy coming to Earth annually is equal to approximately 5·10 20 kcal, or 15.3·10 5 kcal/(m 2 year); however, of these, only 4 x 10 5 , ie, 400,000 kcal, reach the Earth's surface, while the rest of the energy is reflected or absorbed by the atmosphere. The sea covers 71% of the Earth's surface, or 363 million km 2 , while land covers 29%, or 148 million km 2 . On land, the following main types of habitats can be distinguished: forests 40.7 million km 2 or 28% of the land; steppes and prairies 25.7 million km 2 or 17% of the land; arable land 14 million km 2 or 10% of land; natural and artificial deserts (including urban settlements), eternal snows of the highlands and polar regions - 67.7 million km 2 (of which 12.7 million km 2 are in Antarctica) or 45% of the land.
This list was made by Duvigno. American researchers got twice the big numbers. The difference, therefore, is only in absolute values. The ocean provides half of all productivity, forests - a third, and arable land - barely one tenth. All these data are based on the content of carbon dioxide in the atmosphere, which contains approximately 700 billion tons of carbon. The average yield of photosynthesis in relation to the energy supplied to the Earth from the Sun is approximately 0.1%. This is very little. Nevertheless, the total annual production of organic matter and the energy expended on it far exceed those in the total human activity.
While there are relatively reliable data on primary productivity, unfortunately, there is much less data on the productivity of other trophic levels. However, in this case it is not entirely legitimate to talk about productivity; in fact, there is no productivity here, but only the use of food for the formation of a new living substance. It would be more correct to speak of assimilation in relation to these levels.
It is relatively easy to determine the amount of assimilation when it comes to keeping individuals in artificial conditions. However, this is more the subject of physiological than ecological research. The energy balance of an animal for a certain period (for example, per unit of time) is determined by the following equation, the terms of which are expressed not in grams, but in energy equivalents, i.e. in calories: J = NA + PS + R,
where J is the food consumed; NA - unused part of the food thrown out with excrement; PS - secondary productivity of animal tissues (for example, weight gain); R is the energy used to maintain the life of the animal and is expended with respiration.
J and NA are determined using a bomb calorimeter. The value of R can be set by the ratio of the amount of carbon dioxide released to the amount of oxygen absorbed during the same time. Respiratory coefficient R reflects chemical nature oxidized molecules and the energy contained in them. From this, the secondary productivity PS can be deduced. In most cases, it is determined by simple weighing, if the approximate energy value of the synthesized tissues is known. The ability to measure all four terms of the equation makes it possible to estimate the degree of approximation with which their values are obtained. It is not necessary to present too much high requirements especially when working with small animals.
PS/J ratio represents the greatest interest especially for animal husbandry. It expresses the magnitude of assimilation. Sometimes the assimilation yield (PS + R)/J is also used, which corresponds to the fraction of food energy effectively used by the animal, i.e. minus excrement. In detritivorous animals, it is low: for example, in the centipede Glomeris it is 10%, and its assimilation yield lies between 0.5 and 5%. This figure is also low in herbivores: in a pig fed a mixed diet, the yield is 9%, which is already an exception for this trophic level. Caterpillars benefit in this respect due to their poikilothermicity: their assimilation rate reaches 17%. Secondary productivity in carnivores is often higher, but it is highly variable. Testar observed a decrease in assimilation in dragonfly larvae in the course of metamorphosis: in Anax parthenope from 40 to 8%, and in Aeschna suapea, which is characterized by slow growth, from 16 to 10%. In the predatory haymaker Mitopus, assimilation reaches an average of 20%, i.e., it turns out to be very high.
When transferring data obtained in the laboratory to natural populations, their demographic structure must be taken into account. In young individuals, secondary productivity is higher than in adults. It is also necessary to take into account the peculiarities of reproduction, for example, its seasonality and one or another speed. Comparing the populations of the voles Microtus pennsylvanicus and the African elephant, we find quite different assimilation yields: 70 and 30%, respectively. However, the ratio of food consumed to biomass per year is 131.6 for the vole and 10.1 for the elephant. This means that the population of voles annually produces a mass that is two and a half times greater than the original, while the population of elephants is only 1/20 part.
Determining the secondary productivity of ecosystems is very difficult, and we have only indirect data, such as biomass at various trophic levels. Relevant examples have already been given above. Some data lead to the conclusion that primary plant products are used by herbivores, and even more by granivores.
very few animals. The productivity of freshwater fish in lakes and rearing ponds has been thoroughly studied. The productivity of herbivorous fish is always below 10% of net primary production; the productivity of predatory fish is on average 10% in relation to the herbivores they feed on. Naturally, in ponds adapted for developed fish farming, like those in China, herbivorous species are bred. Yields in them, in any case, are higher than in pastoral cattle breeding, and this is quite natural, since mammals are homoiothermic animals. Maintaining a constant body temperature requires high energy costs and is associated with more intense breathing, and this affects secondary productivity. However, in many countries with limited food resources, the consumption of animal foods is a luxury that is too costly in terms of the energy costs of ecosystems. We have to eliminate the floor in the pyramid of energies, in which a person occupies the top, and produce only grain. Multimillion population of India and countries Far East feeds almost entirely on cereals and especially rice.
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