Ecosystem Productivity- this is the accumulation of organic matter by an ecosystem in the course of its life. The productivity of an ecosystem is measured by the amount of organic matter created per unit of time per unit area.

There are different levels of production at which primary and secondary products are created. The organic mass created by producers per unit of time is called primary products, and the increase per unit time of the mass of consumers - secondary products.

Primary production is subdivided into two levels - gross and net production. Gross primary production is the total mass of gross organic matter created by a plant per unit time at a given rate of photosynthesis, including respiration costs.

Plants spend on breathing from 40 to 70% of the gross output. Planktonic algae spend the least of it - about 40% of all energy used. That part of the gross output that is not spent "for breathing" is called net primary production, it represents the amount of plant growth and it is this product that is consumed by consumers and decomposers.

Secondary production is no longer divided into gross and net, since consumers and decomposers, i.e. all heterotrophs, increase their mass due to primary production, i.e. using previously created products.

Secondary production is calculated separately for each trophic level, since it is formed due to the energy coming from the previous level.

All living components of the ecosystem - producers, consumers and decomposers - make up total biomass (live weight) community as a whole or its individual parts, certain groups of organisms. Biomass is usually expressed in terms of wet and dry weight, but can also be expressed in energy units - in calories, joules, etc., which makes it possible to reveal the relationship between the amount of incoming energy and, for example, average biomass.

By the value of biological productivity, ecosystems are divided into 4 classes:

1. very high productivity ecosystems — >2 kg/m2per year (tropical forests, coral reefs);
2. ecosystems of high productivity - 1-2 kg/m 2 per year (linden-oak forests, coastal thickets of cattail or reeds on lakes, crops of corn and perennial grasses during irrigation and application of high doses of fertilizers);
3. ecosystems of moderate productivity - 0.25-1 kg / m 2per year (pine and birch forests, hay meadows and steppes, lakes overgrown with aquatic plants);
4. ecosystems of low productivity —< 0,25 кг/м 2 в год (пустыни, тундра, горные степи, most of marine ecosystems). The average biological productivity of ecosystems on the planet is 0.3 kg/m 2 per year.

The productivity of an ecosystem is closely related to the flow of energy passing through it. In every ecosystem, only part of the incoming energy is stored in the form of organic compounds. The rate of energy assimilation is called production, and the value of production, the ratio to the unit area of ​​the ecosystem is called productivity. The primary productivity (P) of an ecosystem is defined as the rate at which radiant energy is assimilated by producers in the process of photo- and chemosynthesis, accumulating in the form of organic substances, its amount is expressed in the wet or dry phase of plants or energy units (kcal, J). Primary production is determined by the total energy flow through the biotic component of ecosystems, and hence the biomass of living organisms that can exist in a biosystem. In the creation of primary biological production, it is determined by the capabilities of the photosynthetic apparatus of plants. From total 44% of the radiation energy is PAR - photosynthetically active radiation i.e. wavelength of light suitable for photosynthesis. Maximum photosynthesis efficiency 10-12% PAR, which is approximately half of what is theoretically possible. On the globe, the assimilation of solar energy by plants does not exceed 0.1% due to the influence of various factors on plant growth photosynthesis: climatic, physical, chemical.

In the process of production of organic matter, 4 successive levels are distinguished:

1 gross primary productivity is the total production (B) of photosynthesis, taking into account organic substances that were spent on respiration during the measurements (P).

2 net primary productivity of the community (P pure) is the accumulation of organic matter in plant tissues minus the organic matter that was used up for plant respiration.

3 the net productivity of the community is the product of the accumulation of organic matter not consumed by heterotrophs, i.e. the difference between net primary production and the amount of organic matter consumed by heterotrophs.

4 Secondary productivity - energy storage at the level of consumers. consumers use previously created nutrients, some of them are spent on respiration, and the rest on the formation of tissues and organs (secondary production is calculated separately for each living level, since the mass gain for each of them occurs due to the energy supplied by the previous one.

3.4. Homeostasis and Ecosystem Dynamics

Homeostasis is the ability of biological systems (organism, population and ecosystems) to resist changes and maintain balance. Ecosystem management does not require regulation from the outside - it is self-regulating system. Homeostasis at the ecosystem level is provided by a variety of control mechanisms, for example, the “predator-prey” subsystem. If we consider the predator and the prey as conditionally allocated blocks - cybernetic systems, then the control between them should be carried out through positive and negative connections. positive feedback"amplifies the deviation", for example, increases the prey population excessively. negative feedback"reduces deviation", for example, limits the growth of the prey population by increasing the population of predators. This cybernetic scheme perfectly illustrates the process of co-evolution in the "predator-prey" system, since mutual adaptation processes also develop in this "bundle". If other factors do not interfere with this self-regulating system (for example, a person destroyed a predator), then negative and positive connections will balance themselves, otherwise the system will die. In other words, for the existence of an ecosystem, its parameters should not go beyond those limits when it is no longer possible to restore the balance between positive and negative connections.

Ecological balance is the state of an ecosystem in which the composition and productivity of the biotic part (plants, algae, bacteria, animals) at any given time most fully corresponds to abiotic conditions (soil composition, climate). The main feature of ecological balance is its mobility.

There are 2 types of balance mobility:

reversible changes;

ecological successions;

1. Reversible changes in the ecosystem are changes in the ecosystem during the year with climate fluctuations and changes associated with the role of certain species of living organisms depending on the rhythm of their life cycle (change of season, hibernation, bird migration, plants in the seed stage). At the same time, the species composition of the ecosystem is preserved; it only adapts to fluctuations in external and internal factors.

Ecological succession or the law of successional slowdown is a successive change of ecosystems with a gradual change in environmental conditions. At the same time, the composition of living organisms changes, some species leave the ecosystem, while others replenish it, and the productivity of the ecosystem changes accordingly. With sudden changes in environmental conditions (fire, oil spill), the ecological balance is disturbed.

As humanity, with a stubbornness worthy of a better application, turns the face of the Earth into a continuous anthropogenic landscape, the assessment of productivity becomes more and more practical. different ecosystems. Man has learned to obtain energy for his industrial and domestic needs in a variety of ways, but he can obtain energy for his 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. From this diagram, it can be seen that agricultural land, man-made, by no means the most productive ecosystems. 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 grow rapidly. AT long term the fight against desertification and soil erosion, that is, the transformation of unproductive ecosystems into productive ones, is a reasonable way to 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 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 forests cannot be underestimated temperate zone and taiga into the viability of the biosphere. They are especially significant relative stability to anthropogenic impacts compared to 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 capture solar energy in chemical bonds 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 matter 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 the 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, large stocks bedding 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 primary and secondary products, 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 rectangles stacked on top of each other. equal height, the length of which corresponds to the scale of products on 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 the energy relationships in ecosystems, and if the last two are manifested in communities with a certain trophic structure, then the first (production pyramid) has 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. Primary production of agrocenoses and human exploitation natural communities- the main source of food supplies 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 so as not to undermine their productivity. Such calculations are usually very complicated due to methodological difficulties.

The most important bottom line 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.

theoretical possible speed the 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 Northern Arctic Ocean up to more than 200 q/ha per Black Sea coast 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 fisheries on land and in the ocean, can meet less than 50% of needs annually modern population 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 certain period and area, for example, to 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 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 temperate zone- up to 400 tons per 1 ha).

fertile soil deposits, high amount annual temperatures, 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 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.

In the process of life of the biocenosis, organic matter is created and consumed, i.e., the corresponding ecosystem has a certain biomass productivity. Biomass is measured in units of mass or expressed as the amount of energy stored in tissues.

The concepts of "production" and "productivity" in ecology (as well as in biology) have different meanings.

Productivity is the rate of biomass production per unit of time, which cannot be weighed, but can only be calculated in terms of energy or organic matter accumulation. As a synonym for the term "productivity", Y. Odum suggested using the term "production rate".

The productivity of an ecosystem speaks of its "wealth". There are more organisms in a rich or productive community than in a less productive one, although the reverse is sometimes the case, with organisms in a productive community being withdrawn or "turned around" more quickly. Thus, the harvest of grass on the vine of a rich pasture eaten by livestock can be much less than on a less productive pasture to which no livestock has been driven out.

There are also current and general productivity. For example, under certain specific conditions, 1 hectare of pine forest is capable of forming 200 m 3 of wood pulp during the period of its existence and growth - this is its total productivity. However, in one year this forest produces only about 2 m 3 of wood, which is the current productivity or annual increase.

When some organisms are eaten by others, food (matter and energy) moves from one trophic level to the next. The undigested part of the food is thrown out. Animals with a alimentary canal excrete faeces (excrement) and end organic waste products of metabolism (excreta), such as urea; both contain some amount of energy. Both animals and plants lose some of their energy through respiration.

The energy left after losses due to respiration, digestion, excretion, organisms use for growth, reproduction and vital processes (muscle work, maintaining the temperature of warm-blooded animals, etc.). Energy costs for thermoregulation depend on climatic conditions and seasons, the differences between homoiothermic and poikilothermic animals are especially great. Warm-blooded animals, having gained an advantage under adverse and unstable environmental conditions, lost in productivity.

The consumption of energy consumed by animals is determined by the equation

GROWTH + RESPIRATION (LIFE) + REPRODUCTION +

FAECES + EXCRETS = FOOD CONSUMED.

In general, herbivores digest food almost half as efficiently as carnivores. This is because plants contain a large number of cellulose, and sometimes wood (including cellulose and lignin), which are poorly digested and cannot serve as an energy source for most herbivores. The energy contained in excrement and excreta is transferred to detritivores and decomposers, therefore, for the ecosystem as a whole, it is not lost.

Farm animals always, even when kept on pasture on pasture, are distinguished by higher productivity, i.e., the ability to more efficiently use the consumed feed to create products. main reason consists in the fact that these animals are freed from a significant part of the energy costs associated with the search for food, with protection from enemies, bad weather, etc.

The primary productivity of an ecosystem, community, or any part of them is defined as the rate at which solar energy is assimilated by producing organisms (mainly green plants) during photosynthesis or chemical synthesis (chemoproducers). This energy materializes in the form of organic substances of producer tissues.

It is customary to distinguish four successive stages (or stages) of the organic matter production process:

gross primary productivity - the total rate of accumulation of organic substances by producers (the rate of photosynthesis), including those that were spent on respiration and secretory functions. Plants spend about 20% of the produced chemical energy on vital processes;

net primary productivity - the rate of accumulation of organic substances minus those that were consumed during respiration and secretion during the study period. This energy can be used by organisms of the following trophic levels;

community net productivity - the rate of total accumulation of organic matter remaining after consumption by heterotrophic consumers (net primary production minus consumption by heterotrophs). It is usually measured over a period, such as the growing season of plant growth and development, or over a year as a whole;

secondary productivity - the rate of energy storage by consumers. It is not divided into “gross” and “net”, since consumers consume only previously created (ready-made) nutrients, spending them on respiration and secretory needs, and turning the rest into their own tissues. Annually on land, plants form, in terms of dry matter, 1.7 10 11 tons of biomass, equivalent to 3.2 10 18 kJ of energy - this is the net primary productivity. However, taking into account the amount spent on breathing, the gross primary productivity (working capacity) of terrestrial vegetation is about 4.2 10 18 kJ.

Indicators of primary and secondary productivity for the main ecosystems are given in Table. 8.1.

Table 8.1. Primary and secondary productivity of the Earth's ecosystems (according to N. F. Reimers)

ecosystems	Area, mln km2	Average net primary productivity, g / cm 2 per year	Total net primary productivity, billion tons per year	Secondary productivity, million tons per year
Continental (as a whole) including:
tropical rainforests			37,4
temperate evergreen forests			6,5
temperate deciduous forests			8,4
taiga			9,6
savannah			13,5
tundra			1,1
deserts and semi-deserts			1,6
swamps			4,0
lakes and streams			0,5
land cultivated by man			9,1
Marine (in general) including:			55,0
open ocean			41,5
upwellings (water rise zones)	0,4		0,2
continental shelf			9,6
reefs and kelp beds	0,6		1,6
estuaries	1,4		2,1
biosphere (in general)			170,0

The primary production available to heterotrophs, and man belongs specifically to them, is a maximum of 4% of the total solar energy entering the Earth's surface. Since energy is lost at each trophic level, for omnivorous organisms (including humans), the most effective way to extract energy is to consume plant foods (vegetarianism). However, the following must also be considered:

animal protein contains more essential amino acids, and only some legumes (for example, soy) come close to it in value;

Plant protein is more difficult to digest than animal protein, due to the need to first destroy the rigid cell walls;

In a number of ecosystems, animals forage for food over a large area where it is not profitable to grow cultivated plants(these are barren lands where sheep or reindeer graze).

So, in humans, about 8% of proteins are daily excreted from the body (with urine) and re-synthesized. Adequate nutrition requires a balanced supply of amino acids, similar to those found in animal tissues.

In the absence of any amino acid important for the human body (for example, in cereals), a smaller proportion of proteins is absorbed during metabolism. Combining legumes and grains in your diet provides better protein utilization than either of these foods alone.

In more fertile coastal waters, production is confined to the upper layer of water about 30 m thick, and in cleaner but poorer waters high seas the primary production zone may extend as deep as 100 m or less. Therefore, coastal waters appear dark green, while oceanic waters appear blue. In all waters, the peak of photosynthesis falls on the water layer located directly under the surface layer, since the phytoplankton circulating in the water is adapted to twilight lighting and bright sunlight inhibits its life processes.

Similar information.

Primary and secondary production. One of the most important properties ecosystems - the ability to create organic matter, which is called products. Ecosystem productivity is the rate of product 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 water balance 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. As you know, only 44% of solar radiation is 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, 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: lack of heat and moisture, unfavorable soil conditions, etc. Vegetation productivity changes not only during the transition from one climatic 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 Arctic Ocean to 200 c/ha on the Black Sea coast of the 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. Over 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)

ecosystems	Biomass, t/ha	Production, t/ha year
desert	0,1 – 0,5	0,1 – 0,5
Central ocean zones	0,2 – 1,5	0,5 – 2,5
polar seas	1 – 7	3 – 6
Tundra	1 – 8	1 – 4
steppes	5 – 12	3 – 8
Agrocenoses	–	3 – 10
Savannah	8 – 20	4 – 15
Taiga	70 – 150	5 – 10
deciduous forest	100 – 250	10 – 30
Wet a tropical forest	500 – 1500	25 – 60
coral reef	15 – 50	50 – 120

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, an increase in the biological productivity of ecosystems and especially secondary products is one of the critical tasks humanity.

ecological pyramids. Each ecosystem has its own 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 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 food chains, where energy transfer occurs mainly through predator-prey connections, the 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 the oceans and seas, where the main producers are unicellular algae, the biomass pyramid is inverted. 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 full view about functional organization 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 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 energy flows on 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. 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.

Ecosystem dynamics

Ecosystems are constantly changing and developing under the influence of many endogenous and exogenous factors. Dynamism is one of fundamental properties ecosystems, reflecting not only their dependence on a complex of factors, but also the adaptive response of the system as a whole to their impact. All the diverse changes that occur in any community are classified into two main types: cyclical and progressive.

Cyclical changes reflect daily, seasonal and long-term periodicity external conditions and manifestations of endogenous rhythms of organisms.

Daily dynamics of ecosystems mostly related to rhythm. natural phenomena: changes in temperature, humidity, lighting conditions and other factors day and night. As is known, in plants during the day the intensity and nature of physiological processes - photosynthesis, respiration, transpiration - change. In animals, the nature of the activity of those species that differ in the daily rhythm of life activity changes. So, in the forests of the temperate zone during the day, insects, birds and other animals that are distinguished by daytime activity dominate in the biocenosis, at night the activity of nocturnal animal species (moths, owls, nightjars, many mammals, etc.) comes first. In deserts during the daytime at noon, there is a sharp decline in the activity of most species, even those that are distinguished by daytime activity. Moreover, in summer period, when diurnal temperature changes are most extreme, a number of diurnal species change the nature of activity to twilight or even nocturnal (some insects, snakes, etc.).

The separation of periods of activity in time reduces the level of direct competition between the species of the community and thus makes it possible for species with similar ecological requirements to coexist and contributes to a more complete use of environmental resources.

seasonal variability affects more fundamental characteristics of ecosystems. First of all, this concerns the species composition of biocenoses. In unfavorable seasons of the year, some species migrate to areas with the best conditions existence, others endure unfavorable periods in a state of rest, hibernation, stupor, or at the stage of eggs and seeds, i.e. almost completely on certain time years are excluded from the life of the community. In all cases, the decrease in the number active species entails a decrease general level biological cycle substances. Seasonal variability of biocenoses is most clearly expressed in climatic zones characterized by sharp changes in the physical parameters of the environment in summer and winter. In the tropics, it is not so rhythmically expressed, since the length of the day, temperature and humidity change very little during the year.

Long-term variability depends on changes over the years in precipitation, temperature, or other external factors affecting the community. In addition, it can be associated with the characteristics of the life cycle of edificatory plants, with the mass reproduction of animals or pathogenic microorganisms for plants. For example, in dry summers, in normal upland meadows in the forest zone, plant species that have signs of xeromorphic organization and increased resistance to drought often develop predominantly (mountain clover, medium plantain, plain wormwood, silver cinquefoil, etc.), while in wet years their abundance is markedly reduced. Long-term changes in the composition of biocenoses are repeated after periodic climate changes.

In the process of cyclic changes, the integrity of communities is usually preserved. Biocenosis experiences only periodic fluctuations in quantitative and qualitative characteristics.

Progressive changes in an ecosystem result in the replacement of one community by another. The reasons for such changes may be factors external to the biocenosis, long time acting in one direction, for example, waterlogging of soils, increased grazing, etc. The data of the change of one community by another is called exogenous. Changes that lead to a simplification of the community structure, impoverishment of its species composition and a decrease in productivity are called digressions.

Endogenetic Changes arise as a result of processes occurring within the community itself. A natural directed process of community change as a result of the interaction of living organisms with each other and their environment abiotic environment called succession. Succession is based on the incompleteness of the biological cycle in this biocenosis. Populations during long-term existence in the community change the environmental conditions in an unfavorable direction for themselves and are forced out by populations of other species, for which the caused environmental changes turn out to be favorable. Thus, in the community there is a change in the dominant species.

The long-term existence of a biocenosis is possible only if the changes in the environment caused by the activity of some species of organisms are favorable for others with opposite requirements. A successive series of regularly replacing each other in the succession of communities is called successional series.

Successions in nature can be observed everywhere: in puddles and ponds, in leaf litter, on abandoned arable lands, meadows, clearings, etc. Even in stable ecosystems, many local successional changes gradually occur, supporting the complex internal structure of communities.

There are two main types of successional changes: 1) with the participation of both autotrophic and heterotrophic organisms; 2) involving only heterotrophs. Successions of the second type occur only in conditions where there is a supply or a constant supply organic compounds, due to which the community exists, for example, in heaps of manure or compost, accumulations of decaying plant residues, in caves, etc. Successions with change of vegetation can be primary and secondary.

Primary successions begin in places devoid of life - on rocks, loose sands, dumps of the mining industry. The process of succession includes several stages: 1) the emergence of an unoccupied area; 2) migration of organisms or their rudiments to it; 3) their survival in this area; 4) their competition among themselves and the displacement of certain species; 5) transformation of habitats by living organisms, gradual stabilization of conditions and relationships. The introduction of spores, seeds, and the penetration of animals into the vacated area occur by chance and depend on what species are present in the surrounding biotopes. Of the species that have found their way to a new place, only those whose ecological needs correspond to the abiotic conditions of the given habitat are fixed. New species gradually master the biotope, compete with each other and force out the species least adapted to these conditions. Over time, both the restructuring of the community and the transformation of the habitat occur. The main role belongs to the accumulation of dead plant residues or decomposition products. Gradually the soil is formed, change hydrological regime site, its microclimate.

Overgrowing of rocks can serve as an example of primary succession. The community of the first settlers on the rocks is composed of chemotrophic and nitrogen-fixing bacteria and some algae (mainly blue-green and diatoms). The death of these organisms initiates the accumulation of dead organic matter on the stone, which provides food for fungi. Fungi in symbiosis with algae form lichens. Communities of scale lichens destroy the mineral rock with their secretions, which leads to the accumulation of fine earth on the surface of the stone, which holds the dead organic matter and solutions mineral salts. This creates a soil that is already suitable for larger and more demanding plants. Communities of foliose and fruticose lichens and mosses form on it, which displace scale lichens. With the thickening of the layer of fine earth, it becomes possible for herbaceous plants with a superficial root system to take root in it, and then shrubs and trees.

Secondary successions are recovery shifts. They begin where already established communities are partially disturbed, for example, as a result of cutting, fire, grazing, etc. Changes leading to the restoration of the previous composition of the biocenosis are called demutational. An example is the restoration of a spruce forest after cutting down. In the first two years, light-loving herbaceous plants usually grow in clearings - willow-herb, reed grass, stinging nettle, etc. Spruce seedlings on open places are damaged by frost, suffer from overheating and cannot compete with light-loving plants. Soon, numerous seedlings of birch, aspen, and pine appear on the clearing, the seeds of which are easily dispersed by the wind. Trees are replacing light-loving herbaceous plants, and small-leaved or Pine forest, in which conditions favorable for the renewal of spruce arise. When spruce reaches the upper tier, it completely replaces small-leaved trees.

Recovery shifts are faster and easier than primary successions, since the soil profile, seeds, primordia, and part of the former population are preserved in the disturbed community. The rate of ongoing changes in the process of succession is gradually slowing down. Each subsequent stage lasts longer than the previous one. The result of succession is the formation climax community. The initial groupings of species are characterized by the greatest dynamism and instability. Climax communities are capable of long-term self-maintenance, since the circulation of substances in them is balanced. In the course of succession, the species diversity gradually increases, as a result of which the connections within the biocenosis become more complicated and the regulatory capabilities within the system increase. In immature communities, small-sized species with short life cycles and high potential breeding. Gradually, larger forms with long development cycles appear in developing communities. The increase in biological diversity leads to a clearer distribution of organisms according to ecological niches. As a result, communities acquire a certain degree of independence from environmental conditions, not subjecting their lives to change. external environment, but by developing their own endogenous rhythms.

During succession, the total biomass of the system stabilizes. This is because at the first stages of succession, when the species composition of communities is still poor and food chains are short, not all net production is consumed by heterotrophs. Therefore, both the total mass of living organisms and the reserves of dead, undecomposed matter are accumulated. In mature, stable ecosystems, the entire annual growth of vegetation is consumed in the food chains by heterotrophs, so the net production of the biocenosis approaches zero.

Knowledge of these patterns is great importance in practical activities person. Removing the excess of pure products from biocenoses located on initial stages succession, we delay it, but we do not undermine the foundation of the existence of the community. Intervention in climax ecosystems inevitably causes a violation of the existing balance. As long as the disturbances do not exceed the self-healing capacity of the biocenosis, demutative shifts can return it to its original state. But if the force of influence goes beyond these possibilities, then the community gradually degrades, being replaced by derivatives with a low ability to self-renewal.