Ecological pyramids.

Trophic chains could theoretically consist of large number links, but practically do not exceed 5–6 links, since as a result of the action second law of thermodynamics the energy quickly dissipates.

The second law of thermodynamics is also known as the law of increase entropy(Greek entropia turn, transformation). According to this law, energy cannot be created or destroyed - it is transferred from one system to another and transformed from one form to another.

In trophic chains, the amount of plant matter that serves as the basis of the food chain is approximately 10 times greater than the mass of herbivorous animals, and each subsequent food level also has a mass 10 times less. This pattern is called the 10% rule: on average, no more than 1/10 of the energy received from the previous level is transferred to the next trophic level. Therefore, if about one percent of solar energy accumulates in plants, then, for example, at the 4th trophic level its share will be only 0.001%.

Trophic chains represent very unstable systems , since the accidental loss of any link destroys the entire chain. Sustainability of natural communities are ensured by the presence of complex branched multi-species trophic networks . In such networks, when any link falls out, energy begins to move along bypass paths. How more types in biogeocenosis, the more reliable and stable it is.

To visualize the magnitude of the energy transfer coefficient from level to level in the food chains of ecosystems, ecological pyramids of several types are used.

Ecological pyramid – this is a graphical (or diagrammatic) representation of the relationship between volumes organic matter or energy at adjacent levels in the food chain.

The graphic model of the pyramid was developed in 1927 by an American zoologist Charles Elton.

The base of the pyramid is the first trophic level - the level of producers, and the next “floors” of the pyramid are formed by subsequent levels - consumers of various orders. The height of all blocks is the same, and the length is proportional to the number, biomass or energy at the corresponding level. There are three ways to build ecological pyramids

The most widespread types of ecological pyramids are:

Elton's Number Pyramids;

Pyramids of biomass;

Pyramids of energy.

Lindemann's principle. In 1942, based on a generalization of extensive empirical material, the American ecologist Lindeman formulated the principle of transformation of biochemical energy in ecosystems, which was called in environmental literature law 10%.

Lindemann's principle - law of the pyramid of energies (law of 10 percent), according to which, on average, about 10% of the energy received at the previous level of the ecological pyramid passes from one trophic level through food chains to another trophic level. The rest of the energy is lost in the form of thermal radiation, movement, etc. As a result of metabolic processes, organisms lose about 90% of all energy in each link of the food chain, which is spent on maintaining their vital functions.

Elton's number pyramids are presented in the form average number of individuals , required for nutrition of organisms located at subsequent trophic levels.

Pyramid of numbers(abundance) reflects the number of individual organisms at each level (Fig. 35).

For example, to feed one wolf, he needs at least several hares for him to hunt; To feed these hares, you need a fairly large variety of plants.

For example, to represent the food chain:

OAK LEAF – CATERPILLAR – TIT

The pyramid of numbers for one tit (third level) depicts the number of caterpillars (second level) that it eats in a certain time, for example, in one day of light. At the first level of the pyramid, as many oak leaves are depicted as are required to feed the number of caterpillars that are shown at the second level of the pyramid.

Pyramids of biomass and energy express the ratios of the amount of biomass or energy at each trophic level.

The biomass pyramid is based on displaying the results of weighing the dry mass of organic matter at each level, and the energy pyramid is based on calculations of biochemical energy transferred from the underlying to the upper level. These levels on the biomass (or energy) pyramid graph are depicted as rectangles of equal height, the width of which is proportional to the amount of biomass transferred to each subsequent (overlying) level of the trophic chain under study.

GRASS (809) – HERBIVORES (37) – CARNIVORES-1 (11) – CARNIVORES-2 (1.5),

where the values ​​of dry biomass (g/sq. m) are indicated in parentheses.

2. Pyramid of biomass – the ratio of the masses of organisms of different trophic levels. Usually in terrestrial biocenoses the total mass of producers is greater than each subsequent link. In turn, the total mass of first-order consumers is greater than that of second-order consumers, etc. If the organisms do not differ too much in size, the graph usually results in a stepped pyramid with a tapering tip. So, to produce 1 kg of beef you need 70–90 kg of fresh grass.

In aquatic ecosystems, you can also get an inverted, or inverted, pyramid of biomass, when the biomass of producers is less than that of consumers, and sometimes of decomposers. For example, in the ocean, with a fairly high productivity of phytoplankton, its total mass is this moment may be less than that of consumer consumers (whales, large fish, shellfish)

Pyramids of numbers and biomass reflect static systems, i.e., they characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of an ecosystem, although they allow solving a number of practical problems, especially related to maintaining the sustainability of ecosystems.

The pyramid of numbers allows, for example, to calculate the permissible amount of fish catch or shooting of animals during the hunting season without consequences for their normal reproduction.

3. Pyramid of Energy reflects the amount of energy flow, the speed of passage of food mass through the food chain. The structure of the biocenosis is influenced to a greater extent not by the amount of fixed energy, but rate of food production (Fig. 37).

It has been established that the maximum amount of energy transferred to the next trophic level can, in some cases, be 30% of the previous one, and this is in best case scenario. In many biocenoses and food chains, the amount of energy transferred can be only 1%.

Rice. 37. Energy Pyramid: energy flow through the grazing food chain (all figures are in kilojoules per meter squared times the year)

Note that ecological pyramids are a clear illustration of the Lindemann principle and with their help reflect an essential feature of energy processes in ecosystems, namely: due to the relatively small share of energy (on average approximately a tenth) transferred to the next level, very little energy remains in ecosystem, and the rest returns to the geosphere. Thus, with a 4-level trophic chain, only ten thousandth of the biochemical energy remains in the ecosystem. The negligible fraction of energy remaining in the ecosystem explains why in real natural ecosystems food chains have no more than 5–6 levels.

Ecological pyramids

Functional relationships, i.e. trophic structure, can be depicted graphically, in the form of so-called ecological pyramids. The base of the pyramid is the level of producers, and subsequent levels of nutrition form the floors and the top of the pyramid. There are three main types of ecological pyramids: 1) pyramid of numbers, reflecting the number of organisms at each level (Elton’s pyramid); 2) biomass pyramid, characterizing the mass of living matter - total dry weight, calorie content, etc.; 3) product pyramid(or energy), having a universal character, showing changes in primary production (or energy) at successive trophic levels.

The pyramid of numbers displays a clear pattern discovered by Elton: the number of individuals making up a sequential series of links from producers to consumers is steadily decreasing (Fig. 5.). This pattern is based, firstly, on the fact that to balance the mass of a large body, many small bodies are needed; secondly, an amount of energy is lost from lower to higher trophic levels (only 10% of energy reaches the previous level from each level) and, thirdly, there is an inverse relationship between metabolism and the size of individuals (the smaller the organism, the more intense the metabolism, the higher the growth rate their numbers and biomass).

Rice. 5. Simplified diagram of Elton's pyramid

However, population pyramids will vary greatly in shape in different ecosystems, so it is better to present numbers in tabular form, but biomass in graphical form. It clearly indicates the amount of all living matter at a given trophic level, for example, in units of mass per unit area - g/m2 or volume - g/m3, etc.

In terrestrial ecosystems the following rule applies: biomass pyramids: the total mass of plants exceeds the mass of all herbivores, and their mass exceeds the entire biomass of predators. This rule is observed, and the biomass of the entire chain changes with changes in the value of net production, the ratio of the annual increase of which to the biomass of the ecosystem is small and varies in forests of different geographical zones from 2 to 6%. And only in meadow plant communities it can reach 40-55%, and in some cases, in semi-deserts - 70-75%. In Fig. Figure 6 shows pyramids of biomass of some biocenoses. As can be seen from the figure, for the ocean the above rule of the biomass pyramid is invalid - it has an inverted (reversed) appearance.

Rice. 6. Pyramids of biomass of some biocenoses: P - producers; RK - herbivorous consumers; PC - carnivorous consumers; F – phytoplankton; Z - zooplankton

The ocean ecosystem is characterized by a tendency for biomass to accumulate at high levels among predators. Predators live long and the turnover rate of their generations is low, but for producers - phytoplanktonic algae - the turnover rate can be hundreds of times higher than the biomass reserve. This means that their net production here also exceeds the production absorbed by consumers, i.e., more energy passes through the level of producers than through all consumers.

Hence it is clear that an even more perfect reflection of the influence of trophic relationships on the ecosystem should be the rule of the product (or energy) pyramid: at each previous trophic level, the amount of biomass created per unit of time (or energy) is greater than at the next one.

Trophic or food chains can be represented in the shape of a pyramid. The numerical value of each step of such a pyramid can be expressed by the number of individuals, their biomass or the energy accumulated in it.

In accordance with the law of the pyramid of energies of R. Lindemann and the rule of ten percent, from each stage approximately 10% (from 7 to 17%) of energy or matter in energy terms passes to the next stage (Fig. 7). Note that at each subsequent level, as the amount of energy decreases, its quality increases, i.e. the ability to do work per unit of animal biomass is a corresponding number of times higher than the same amount of plant biomass.

A striking example is the food chain of the open sea, represented by plankton and whales. The mass of plankton is dispersed in ocean water and, with the bioproductivity of the open sea less than 0.5 g/m 2 day -1, the amount of potential energy in a cubic meter of ocean water is infinitesimal compared to the energy of a whale, whose mass can reach several hundred tons. As you know, whale oil is a high-calorie product that was even used for lighting.

In accordance with the last figure it is formulated one percent rule: for the stability of the biosphere as a whole, the share of possible final consumption of net primary production in energy terms should not exceed 1%.

Fig.7. Pyramid of energy transfer along the food chain (according to Yu. Odum)

A corresponding sequence is also observed in the destruction of organic matter: about 90% of the energy of pure primary production is released by microorganisms and fungi, less than 10% by invertebrate animals and less than 1% by vertebrate animals, which are the final cosumentors.

Ultimately, all three rules of the pyramids reflect energy relations in the ecosystem, and the pyramid of products (energy) has a universal character.

In nature, in stable systems, biomass changes slightly, i.e. nature tends to use the entire gross production. Knowledge of the energy of an ecosystem and its quantitative indicators make it possible to accurately take into account the possibility of removing a certain amount of plant and animal biomass from the natural ecosystem without undermining its productivity.

Man receives quite a lot of products from natural systems, however, the main source of food for him is agriculture. Having created agroecosystems, a person strives to obtain as much pure vegetation products as possible, but he needs to spend half of the plant mass on feeding herbivores, birds, etc., a significant part of the products goes to industry and is lost in waste, i.e., it is also lost here about 90% is pure production and only about 10% is directly used for human consumption.

In natural ecosystems, energy flows also change in intensity and character, but this process is regulated by the action environmental factors, which is manifested in the dynamics of the ecosystem as a whole.

Relying on the food chain as the basis for the functioning of the ecosystem, it is also possible to explain cases of accumulation in the tissues of certain substances (for example, synthetic poisons), which, as they move along the food chain, do not participate in the normal metabolism of organisms. According to rules of biological enhancement There is an approximately tenfold increase in the concentration of the pollutant when switching to more high level ecological pyramid. In particular, a seemingly insignificant increased content of radionuclides in river water at the first level of the trophic chain is assimilated by microorganisms and plankton, then concentrated in the tissues of fish and reaches maximum values ​​in gulls. Their eggs have a level of radionuclides 5000 times higher than background contamination.

Types of ecosystems:

There are several classifications of ecosystems. First, ecosystems are divided by nature of origin and are divided into natural (swamp, meadow) and artificial (arable land, garden, spaceship).

By size ecosystems are divided into:

1. microecosystems (for example, the trunk of a fallen tree or a clearing in the forest)

2. mesoecosystems (forest or steppe forest)

3. macroecosystems (taiga, sea)

4. ecosystems at the global level (planet Earth)

Energy is the most convenient basis for classifying ecosystems. There are four fundamental types of ecosystems based on type of energy source:

1. driven by the Sun, poorly subsidized
2. driven by the Sun, subsidized by other natural sources
3. driven by the Sun and subsidized by man
4. driven by fuel.

In most cases, two energy sources can be used - the Sun and fuel.

Natural ecosystems driven by the sun, little subsidized- these are open oceans, high mountain forests. All of them receive energy almost exclusively from one source - the Sun and have low productivity. Annual energy consumption is estimated at approximately 10 3 -10 4 kcal-m 2. Organisms living in these ecosystems are adapted to the scarce amount of energy and other resources and use them efficiently. These ecosystems are very important for the biosphere, as they occupy vast areas. The ocean covers about 70% of the surface globe. In fact, these are the main life support systems, mechanisms that stabilize and maintain conditions on the “ spaceship" - Earth. Here, huge volumes of air are purified every day, water is returned to circulation, climatic conditions are formed, temperature is maintained, and other life-sustaining functions are performed. In addition, some food and other materials are produced here without any human input. It should also be said about the aesthetic values ​​of these ecosystems that cannot be taken into account.

Natural ecosystems driven by the Sun, subsidized by other natural sources, are ecosystems that are naturally fertile and produce excess organic matter that can accumulate. They receive natural energy subsidies in the form of energy from tides, surf, currents coming from the catchment area with rain and wind, organic and minerals etc. Energy consumption in them ranges from 1*10 4 to 4*10 4 kcal*m -2 *year -1. The coastal part of the estuary such as the Neva Bay - good example ecosystems that are more fertile than adjacent land areas receiving the same amount of solar energy. Excessive fertility can also be observed in rain forests.

Ecosystems driven by the sun and subsidized by humans, are terrestrial and aquatic agroecosystems that receive energy not only from the Sun, but also from humans in the form of energy subsidies. Their high productivity is supported by muscle energy and fuel energy, which are spent on cultivation, irrigation, fertilization, selection, processing, transportation, etc. Bread, corn, potatoes are “partly made from oil.” The most productive agriculture receives approximately the same amount of energy as the most productive natural ecosystems second type. Their production reaches approximately 50,000 kcal*m -2 year -1 . The difference between them is that man directs as much energy as possible to the production of a limited type of food, while nature distributes it among many types and accumulates energy for a rainy day, as if putting it in different pockets. This strategy is called the “diversity-for-survival strategy.”

Industrial-urban ecosystems driven by fuel, is the crowning achievement of humanity. In industrial cities, highly concentrated fuel energy does not complement, but replaces solar energy. Food, a product of systems driven by the Sun, is brought into the city from outside. A feature of these ecosystems is the enormous energy demand of densely populated urban areas - it is two to three orders of magnitude greater than in the first three types of ecosystems. If in unsubsidized ecosystems the energy influx ranges from 10 3 to 10 4 kcal*m -2 year -1 , and in subsidized systems of the second and third types - from 10 4 to 4*10 4 kcal*m -2 year -1 , then in In large industrial cities, energy consumption reaches several million kilocalories per 1 m 2: New York -4.8 * 10 6, Tokyo - 3 * 10 6, Moscow - 10 6 kcal * m -2 year -1.

Human energy consumption in the city averages more than 80 million kcal*year -1 ; for nutrition it requires only about 1 million kcal*year -1, therefore, for all other types of activities ( household, transport, industry, etc.) a person spends 80 times more energy than is required for the physiological functioning of the body. Of course, in developing countries the situation is somewhat different.

>> Ecological pyramids

Ecological pyramids

1. What is a food web?
2. 2 What organisms are producers?
3. How do consumers differ from producers?

Energy transfer in a community.

In any trophic chain, not all food is used for the growth of individuals, that is, for the formation of biomass. Part of it is spent on satisfying the energy costs of organisms: breathing, movement, reproduction, maintaining body temperature, etc. Consequently, in each subsequent link the food chain biomass decreases. Typically, the greater the mass of the initial link of a food chain, the greater it is in subsequent links.

The food chain is the main channel for energy transfer in a community. As you move away from the primary producer, its quantity decreases. This is due to a number of reasons.

The transfer of energy from one level to another is never complete. Some of the energy is lost during the processing of food, and some is not absorbed by the body at all and is excreted from it with excrement, and then decomposed by destructors.

Some energy is lost as heat during breathing. Any animal, moving, hunting, building a nest or performing other actions, performs work that requires energy, as a result of which heat is released again.

The drop in the amount of energy during the transition from one trophic level to another (higher) determines the number of these levels and the ratio of predators and prey. It is estimated that any given trophic level receives about 10% (or slightly more) of the energy of the previous level. That's why total number There are rarely more than four to six trophic levels.

This phenomenon, depicted graphically, is called the ecological pyramid. There are a pyramid of numbers (individuals), a pyramid of biomass and a pyramid of energy.

The base of the pyramid is formed by producers ( plants). Above them are consumers of the first order (herbivores). The next level is represented by second-order consumers (predators). And so on until the top of the pyramid, which is occupied by the largest predators. The height of the pyramid usually corresponds to the length of the food chain.

The biomass pyramid shows the ratio of the biomass of organisms of different trophic levels, depicted graphically in such a way that the length or area of ​​the rectangle corresponding to a certain trophic level is proportional to its biomass (Fig. 136).

The concept of trophic levels

Trophic level is a collection of organisms that occupy a certain position in the overall food chain. Organisms that receive their energy from the Sun through the same number of steps belong to the same trophic level.

Such a sequence and subordination of groups of organisms connected in the form of trophic levels represents the flow of matter and energy in an ecosystem, the basis of its organization.

Trophic structure of the ecosystem

As a result of the sequence of energy transformations in food chains, each community of living organisms in an ecosystem acquires a certain trophic structure. The trophic structure of a community reflects the relationship between producers, consumers (separately of the first, second, etc. orders) and decomposers, expressed either by the number of individuals of living organisms, or their biomass, or the energy contained in them, calculated per unit area per unit time.

Trophic structure is usually depicted as ecological pyramids. This graphic model was developed in 1927 by the American zoologist Charles Elton. The base of the pyramid is the first trophic level - the level of producers, and the next floors of the pyramid are formed by subsequent levels - consumers of various orders. The height of all blocks is the same, and the length is proportional to the number, biomass or energy at the corresponding level. There are three ways to build ecological pyramids.

1. Pyramid of numbers (abundance) reflects the number of individual organisms at each level. For example, to feed one wolf, he needs at least several hares for him to hunt; To feed these hares, you need a fairly large variety of plants. Sometimes pyramids of numbers can be reversed, or upside down. This applies to forest food chains, where trees serve as producers and insects serve as primary consumers. In this case, the level of primary consumers is numerically richer than the level of producers (a large number of insects feed on one tree).

2. Pyramid of biomass - the ratio of the masses of organisms of different trophic levels. Usually in terrestrial biocenoses the total mass of producers is greater than each subsequent link. In turn, the total mass of first-order consumers is greater than that of second-order consumers, etc. If the organisms do not differ too much in size, the graph usually results in a stepped pyramid with a tapering tip. So, to produce 1 kg of beef you need 70-90 kg of fresh grass.

In aquatic ecosystems, you can also get an inverted, or inverted, pyramid of biomass, when the biomass of producers is less than that of consumers, and sometimes of decomposers. For example, in the ocean, with a fairly high productivity of phytoplankton, its total mass at a given moment may be less than that of consumer consumers (whales, large fish, shellfish).

Pyramids of numbers and biomass reflect static systems, i.e., they characterize the number or biomass of organisms in a certain period of time. They do not provide complete information about the trophic structure of an ecosystem, although they allow solving a number of practical problems, especially related to maintaining the sustainability of ecosystems. The pyramid of numbers allows, for example, to calculate the permissible amount of fish catch or shooting of animals during the hunting season without consequences for their normal reproduction.

3. Pyramid of Energy reflects the amount of energy flow, the speed of passage of food mass through the food chain. The structure of the biocenosis is influenced to a greater extent not by the amount of fixed energy, but by the rate of food production.

It has been established that the maximum amount of energy transferred to the next trophic level can in some cases be 30% of the previous one, and this is in the best case. In many biocenoses and food chains, the amount of energy transferred can be only 1%.

In 1942, the American ecologist R. Lindeman formulated law of the pyramid of energies (law of 10 percent) , according to which, on average, about 10% of the energy received at the previous level of the ecological pyramid passes from one trophic level through food chains to another trophic level. The rest of the energy is lost in the form of thermal radiation, movement, etc. As a result of metabolic processes, organisms lose about 90% of all energy in each link of the food chain, which is spent on maintaining their vital functions.

If a hare ate 10 kg of plant matter, then its own weight may increase by 1 kg. A fox or wolf, eating 1 kg of hare meat, increases its mass by only 100 g. In woody plants, this proportion is much lower due to the fact that wood is poorly absorbed by organisms. For grasses and seaweeds, this value is much greater, since they do not have difficult-to-digest tissues. However, the general pattern of the energy transfer process remains: through the upper trophic levels it passes much less than through the lower ones.

This is why food chains usually cannot have more than 3-5 (rarely 6) links, and ecological pyramids cannot consist of large quantity floors. The final link of the food chain, just like the top floor of the ecological pyramid, will receive so little energy that it will not be enough if the number of organisms increases.

This statement can be explained by tracing where the energy of consumed food is spent: part of it goes to the construction of new cells, i.e. growth, part of the food energy is spent on energy metabolism or respiration. Since the digestibility of food cannot be complete, i.e. 100%, then part of the undigested food in the form of excrement is removed from the body.

Considering that the energy spent on respiration is not transferred to the next trophic level and leaves the ecosystem, it becomes clear why each subsequent level will always be less than the previous one.

This is why large predatory animals are always rare. Therefore, there are also no predators that feed on wolves. In this case, they simply would not have enough food, since wolves are few in number.

The trophic structure of an ecosystem is expressed in complex food relationships between its constituent species. Ecological pyramids of numbers, biomass and energy, depicted in the form of graphic models, express the quantitative relationships of organisms with different feeding methods: producers, consumers and decomposers.

Each ecosystem consists of several trophic (food) levels, forming a certain structure. Trophic structure usually depicted as ecological pyramids.

In 1927, the American ecologist and zoologist Charles Elton proposed a graphical model ecological pyramid. The base of the pyramid is the first trophic level, consisting of producers. Above are the levels of consumers of various orders. In other words, looking at the ecological pyramid, we understand how all its members relate to several factors in a given ecosystem.

Levels are displayed an ecological pyramid in the form of several rectangular or trapezoidal tiers, the size of which is correlated either with the number of participants at each level of the food chain, or with their mass, or with energy.

Three types of ecological pyramids

1. Pyramid of numbers (or numbers) tells us the number of living organisms at each level. For example, to feed one owl, 12 mice are needed, and they, in turn, need 300 ears of rye. It often happens that the pyramid of numbers is inverted (such a pyramid is also called inverted). It can describe, say, a forest food chain in which trees are the producers and insects are the primary consumers. One tree provides food for myriads of insects.

2. Biomass pyramid describes ratio of masses of organisms of several trophic levels. As a rule, in biocenoses on land, the mass of producers is much greater than in each subsequent link of the food chain, and the mass of consumers of the first level exceeds the mass of consumers of the second level, etc.

Aquatic ecosystems can also be characterized by inverted pyramids of biomass, in which the mass of consumers is greater than the mass of producers. Oceanic zooplankton feeding on phytoplankton greatly exceeds it in total mass. It would seem that with such a rate of absorption, phytoplankton should disappear, however, it is saved by a high growth rate.

3. Pyramid of Energy explores the amount of energy flowing through a food chain from the base level to the highest level. The structure of the biocenosis highly depends on the rate of food production at all trophic levels. American scientist Raymond Lindeman found that at each level up to 90% of the energy received at it is lost (the so-called “Law of 10%”).

Why are ecological pyramids needed?

Pyramids of numbers and biomass describe the ecosystem in its statics, since they calculate the number or mass of participants in the ecosystem for a fixed time period. They are not intended to provide information about the trophic structure of the ecosystem in dynamics, however, they allow solving problems related to maintaining the stability of the ecosystem and anticipating possible dangers.

A classic example of a violation of sustainability is the introduction of rabbits to the Australian continent. Due to the high rate of reproduction, their numbers became so huge that they caused harm agriculture, depriving sheep and cattle of food - thus only one species The consumers (rabbits) are monopolized by the producer (grass) in this ecosystem.

Pyramid of Energy, unlike the above-mentioned pyramids, is dynamic, it transmits the speed of passage of the amount of energy through all trophic levels. Its task is to give an idea of ​​the functional organization ecosystems.