The main process that occurs in all ecosystems is the transfer and circulation of matter or energy. However, losses are inevitable. The magnitude of these losses from level to level is what the rules of ecological pyramids reflect.
Some academic terms
The exchange of matter and energy is a directed flow in the chain of producers - consumers. Simply put, the eating of some organisms by others. At the same time, a chain or sequence of organisms is built, which, as links in the chain, are connected by the relationship "food - consumer". This sequence is called the trophic or food chain. And the links in it are trophic levels. The first level of the chain is producers (plants), because only they can form organic substances from inorganic ones. The next links are consumers (animals) of various orders. Herbivores are consumers of the 1st order, and predators that feed on herbivores will be consumers of the 2nd order. The next link in the chain will be decomposers - organisms whose food is the remains of life or the corpses of living organisms.
Graphic pyramids
The British ecologist Charles Elton (1900-1991) in 1927, based on the analysis of quantitative changes in food chains, introduced the concept of ecological pyramids into biology as a graphic illustration of the ratios in the ecosystem of producers and consumers. Elton's pyramid is depicted as a triangle divided by the number of links in the chain. Or in the form of rectangles standing on top of each other.
Patterns of the pyramid
C. Elton analyzed the number of organisms in chains and found that there are always more plants than animals. Moreover, the ratio of levels in quantitative terms is always the same - a decrease occurs at each next level, and this is an objective conclusion, which is reflected in the rules of ecological pyramids.
Elton's rule
This rule states that the number of individuals in a sequence decreases from level to level. The rules of the ecological pyramid are the quantitative ratio of the products of all levels of a particular food chain. It says that the chain level indicator will be approximately 10 times less than that of the previous level.
Given a simple example that will dot the "and". Consider the trophic chain of algae - invertebrate crustaceans - herring - dolphin. A 40 kg dolphin needs to eat 400 kg of herring to live. And in order for these 400 kilograms of fish to exist, about 4 tons of their food is needed - invertebrate crustaceans. For the formation of 4 tons of crustaceans, 40 tons of algae are already needed. This is what the rules of the ecological pyramid reflect. And only in such a ratio will this ecological structure be sustainable.
Types of ecopyramids
Based on the criterion that will be taken into account when evaluating the pyramids, there are:
- Numeric.
- Biomass estimates.
- Energy costs.
In all cases, the rule of the ecological pyramid reflects a decrease in the main evaluation criterion by 10 times.
Number of individuals and trophic steps
In the pyramid of numbers, the number of organisms is taken into account, which is reflected in the rule of the ecological pyramid. And the example with the dolphin fully fits the description of this type of pyramids. But there are exceptions - a forest ecosystem with a chain of plants - insects. The pyramid will become inverted (a huge number of insects feeding on one tree). That is why the pyramid of numbers is considered not the most informative and indicative.
And what's left?
The biomass pyramid uses the dry (rarely wet) mass of individuals of the same level as an evaluation criterion. Units of measurement - gram / square meter, kilogram / hectare or gram / cubic meter. But even here there are exceptions. The rules of ecological pyramids, which reflect a decrease in the biomass of consumers in relation to the biomass of producers, are carried out for biocenoses, where both are large and have a long life cycle. But for water systems, the pyramid can again be inverted. For example, in the seas, the biomass of zooplankton feeding on algae is sometimes 3 times greater than the biomass of plant plankton itself. saves the high rate of reproduction of phytoplankton.
Energy flow is the most accurate indicator
Pyramids of energy show the speed of passage of food (its mass) through trophic levels. The law of the pyramid of energy was formulated by the outstanding ecologist from America Raymond Lindeman (1915-1942), after his death in 1942 he entered biology as a rule of ten percent. According to it, 10% of the energy from the previous one goes to each subsequent level, the remaining 90% are losses that go to support the body's vital functions (breathing, heat regulation).
The meaning of the pyramids
We have analyzed what the rules of ecological pyramids reflect. But why do we need this knowledge? Pyramids of numbers and biomass make it possible to solve some practical problems, since they describe the static and stable state of the system. For example, they are used in calculating the allowable values of the catch of fish or counting the number of animals for shooting, so as not to disturb the stability of the ecosystem and determine the maximum size of a particular population of individuals for a given ecosystem in its entirety. And the energy pyramid gives clear view about the organization of functional communities, allows you to compare different ecosystems in terms of their productivity.
Now the reader will not be at a loss, having received a task like “describe what the rules of ecological pyramids reflect”, and boldly answer that these are the loss of matter and energy in a specific trophic chain.
In any trophic chain, not all food is used for the growth of an individual, i.e. for the accumulation of its biomass. Part of it is spent to meet the energy costs of the body (breathing, movement, reproduction, maintaining body temperature).
At the same time, the biomass of one link cannot be completely processed by the next, and in each subsequent link of the trophic chain, a decrease in biomass occurs.
On average, it is believed that only about 10% of the biomass and the energy associated with it passes from each trophic level to the next, i.e. the production of organisms of each subsequent trophic level is always less on average 10 times the production of the previous level.
So, for example, on average, 100 kg of biomass of herbivorous animals (consumers of the first order) is formed from 1000 kg of plants. Carnivores (second-order consumers) that eat herbivores can synthesize 10 kg of their biomass from this amount, while predators (third-order consumers) that feed on carnivores synthesize only 1 kg of their biomass.
Thus , the total biomass, the energy contained in it, as well as the number of individuals progressively decrease as one ascends the trophic levels.
This pattern has been named ecological pyramid rules.
This phenomenon was first studied by C. Elton (1927) and named by him pyramid of numbers or Elton's pyramid.
ecological pyramid - this is a graphic representation of the relationship between producers and consumers of different orders, expressed in units of biomass (pyramid of biomass), number of individuals (population pyramid) or the energy contained in the mass of living matter (pyramid of energy) ( Fig.6).
Fig.6. Diagram of the ecological pyramid.
The ecological pyramid expresses the trophic structure of ecosystems in geometric form.
There are three main types of ecological pyramids: the pyramid of numbers (numbers), the pyramid of biomass and the pyramid of energy.
1) pyramids of numbers, based on the count of organisms of each trophic level; 2) biomass pyramids, which use the total mass (usually dry) of organisms at each trophic level; 3) energy pyramids, taking into account the energy intensity of organisms of each trophic level.
energy pyramids are considered the most important, since they directly refer to the basis of nutritional relationships - the flow of energy necessary for the life of any organisms.
Pyramid of numbers (numbers)
The pyramid of numbers (numbers) or Elton's pyramid reflects the number of individual organisms at each trophic level.
The population pyramid is the simplest approximation to the study of the trophic structure of an ecosystem.
At the same time, the number of organisms in a given area is first calculated, grouping them by trophic levels and presenting them as a rectangle, the length (or area) of which is proportional to the number of organisms living in a given area (or in a given volume, if it is an aquatic ecosystem).
The population pyramid can have a regular shape, i.e. taper upwards (correct or straight), and may be an inverted top downwards (inverted or reversed) fig.7.
right (straight) inverted (inverted)
(pond, lake, meadow, steppe, pasture, etc.) (temperate forest in summer, etc.)
Fig.7. Pyramid of numbers (1 - correct; 2 - inverted)
The population pyramid has a regular shape, i.e. narrows when moving from the level of producers to higher trophic levels, for aquatic ecosystems (pond, lake, etc.) and terrestrial ecosystems (meadow, steppe, pasture, etc.).
For example:
1,000 phytoplankton small pond can feed 100 individuals of small crustaceans - consumers of the first order, which in turn will feed 10 individuals of fish - consumers of the second order, which will be enough to feed 1 perch - consumer of the third order.
The abundance pyramid for some ecosystems, such as temperate forests, is inverted.
For example:
in the temperate forest in the summer a small amount big trees- producers are supplied with food by a huge number of small-sized phytophage insects and birds - consumers of the first order.
However, in ecology, the population pyramid is rarely used, since due to the large number of individuals at each trophic level, it is very difficult to display the structure of the biocenosis on the same scale.
biomass pyramid
The biomass pyramid reflects more fully the nutritional relationships in the ecosystem, since it takes into account the total mass of organisms (biomass) of each trophic level.
Rectangles in biomass pyramids display the mass of organisms of each trophic level, per unit area or volume.
Pyramids of biomass, as well as pyramids of abundance, can be not only regular in shape, but also inverted (reversed) Fig.8.
Consumers of the 3rd order
Consumers of the 2nd order
Consumers of the 1st order
Producers
right (straight) inverted (inverted)
(terrestrial ecosystems: (aquatic ecosystems: lake,
meadow, field, etc.) pond and especially marine
ecosystems)
Fig.7. Pyramid of biomass (1 - correct; 2 - inverted)
For most terrestrial ecosystems (meadow, field, etc.), the total biomass of each subsequent trophic level of the food chain decreases.
This creates a biomass pyramid, where producers significantly predominate, and gradually decreasing trophic levels of consumers are located above them, i.e. the biomass pyramid has a regular shape.
For example:
on average, out of 1000 kg of plants, 100 kg of the body of herbivorous animals are formed - consumers of the first order (phytophages). Carnivorous animals - consumers of the second order, eating herbivores, can synthesize 10 kg of their biomass from this amount. And predators - consumers of the third order, eating carnivores, synthesize only 1 kg of their biomass.
In aquatic ecosystems (lake, pond, etc.), the biomass pyramid can be inverted, where the biomass of consumers prevails over the biomass of producers.
This is explained by the fact that in aquatic ecosystems the producer is microscopic phytoplankton, which rapidly grows and reproduces), which continuously supplies live food in sufficient quantities to consumers who grow and reproduce much more slowly. Zooplankton (or other animals that feed on phytoplankton) accumulate biomass over years and decades, while phytoplankton have an extremely short life span (several days or hours).
1. Pyramids of numbers- at each level, the number of individual organisms is plotted.
The pyramid of numbers reflects a distinct pattern discovered by Elton: the number of individuals that make up a sequential series of links from producers to consumers is steadily decreasing (Fig. 3).
For example, to feed one wolf, you need at least a few hares that he could hunt; to feed these hares, you need a fairly large number of various plants. In this case, the pyramid will look like a triangle with a wide base tapering upwards.
However, this form of the pyramid of numbers is not typical for all ecosystems. Sometimes they can be reversed, or inverted. This applies to forest food chains, when trees serve as producers, and insects 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), so the pyramids of numbers are the least informative and least indicative, i.e. the number of organisms of the same trophic level largely depends on their size.
2. biomass pyramids- characterizes the total dry or wet mass of organisms at a given trophic level, for example, in units of mass per unit area - g / m 2, kg / ha, t / km 2 or per volume - g / m 3 (Fig. 4)
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 second-order consumers, and so on.
In this case (if the organisms do not differ too much in size), the pyramid will also look like a triangle with a wide base tapering upwards. However, there are significant exceptions to this rule. For example, in the seas, the biomass of herbivorous zooplankton is significantly (sometimes 2-3 times) greater than the biomass of phytoplankton, which is represented mainly by unicellular algae. This is explained by the fact that algae are very quickly eaten away by zooplankton, but the very high rate of division of their cells protects them from complete eating.
In general, terrestrial biogeocenoses, where producers are large and live relatively long, are characterized by relatively stable pyramids with a wide base. In aquatic ecosystems, where producers are small in size and have short life cycles, the biomass pyramid can be reversed or inverted (pointed downwards). So, in lakes and seas, the mass of plants exceeds the mass of consumers only during the flowering period (spring), and in the rest of the year the situation may be reversed.
Pyramids of numbers and biomass reflect the statics of the system, i.e., they characterize the number or biomass of organisms in a certain period of time. They don't give complete information about the trophic structure of the ecosystem, although they allow solving a number of practical problems, especially those related to maintaining the stability of ecosystems.
The pyramid of numbers makes it possible, for example, to calculate the allowable value of catching fish or shooting animals during the hunting period without consequences for their normal reproduction.
3. energy pyramids- shows the magnitude of the energy flow or productivity at successive levels (Fig. 5).
In contrast to the pyramids of numbers and biomass, which reflect the statics of the system (the number of organisms at a given moment), the pyramid of energy, reflecting the picture of the speed of passage of a mass of food (amount of energy) through each trophic level of the food chain, gives the most complete picture of the functional organization of communities.
The shape of this pyramid is not affected by changes in the size and intensity of metabolism of individuals, and if all sources of energy are taken into account, then the pyramid will always have a typical appearance with a wide base and a tapering top. When building a pyramid of energy, a rectangle is often added to its base, showing the influx of solar energy.
In 1942, the American ecologist R. Lindeman formulated the law of the pyramid of energies (the law of 10 percent), according to which, on average, about 10% of the energy received by 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. Organisms, as a result of metabolic processes, lose about 90% of all the energy that is expended to maintain their vital activity in each link of the food chain.
If a hare ate 10 kg of plant matter, then its own weight could increase by 1 kg. A fox or a wolf, eating 1 kg of hare, increases its mass by only 100 g. woody plants this proportion is much lower due to the fact that wood is poorly absorbed by organisms. For grasses and algae, this value is much higher, since they do not have hard-to-digest tissues. However, the general regularity of the process of energy transfer remains: much less energy passes through the upper trophic levels than through the lower ones.
Consider the transformation of energy in an ecosystem using the example of a simple pasture trophic chain, in which there are only three trophic levels.
1. Level - herbaceous plants,
2. Level - herbivorous mammals, for example, hares
3. Level - predatory mammals, for example, foxes
Nutrients are created in the process of photosynthesis by plants, which from inorganic substances (water, carbon dioxide, mineral salts, etc.) using the energy of sunlight form organic substances and oxygen, as well as ATP. Part of the electromagnetic energy of solar radiation is then converted into the energy of chemical bonds of synthesized organic substances.
All organic matter created during photosynthesis is called gross primary production (GPP). Part of the energy of gross primary production is spent on respiration, resulting in the formation of net primary production (NPP), which is the very substance that enters the second trophic level and is used by hares.
Let the runway be 200 conventional units energy, and the costs of plants for respiration (R) - 50%, i.e. 100 conventional units of energy. Then the net primary production will be equal to: NPP = WPP - R (100 = 200 - 100), i.e. at the second trophic level, hares will receive 100 conventional units of energy.
However, for various reasons, hares are able to consume only a certain proportion of NPP (otherwise, resources for the development of living matter would disappear), but a significant part of it, in the form of dead organic residues (underground parts of plants, hard wood of stems, branches, etc. .) is not able to be eaten by hares. It enters detritus food chains and (or) is decomposed by decomposers (F). The other part goes to building new cells (population size, growth of hares - P) and ensuring energy metabolism or respiration (R).
In this case, according to the balance approach, the balance equation of energy consumption (C) will look like this: C = P + R + F, i.e. the energy received at the second trophic level will be spent, according to Lindemann's law, for population growth - P - 10%, the remaining 90% will be spent on breathing and removing undigested food.
Thus, in ecosystems with an increase in the trophic level, there is a rapid decrease in the energy accumulated in the bodies of living organisms. From this it is clear why each subsequent level will always be less than the previous one and why food chains usually cannot have more than 3-5 (rarely 6) links, and ecological pyramids cannot consist of a large number floors: the final link of the food chain, as well as the top floor of the ecological pyramid, will receive so little energy that it will not be enough if the number of organisms increases.
Such a sequence and subordination of groups of organisms connected in the form of trophic levels is the flow of matter and energy in the biogeocenosis, the basis of its functional organization.
The most important type of relationship between organisms in a biocenosis, which actually form its structure, is the food connections of a predator and prey: some are eaters, others are eaten. At the same time, all organisms, living and dead, are food for other organisms: a hare eats grass, a fox and a wolf hunt hares, birds of prey (hawks, eagles, etc.) are able to drag and eat both a fox cub and a wolf cub. Dead plants, hares, foxes, wolves, birds become food for detritivores (decomposers or otherwise destructors).
A food chain is a sequence of organisms in which each eats or decomposes the other. It represents the path of a unidirectional flow of a small part of the highly efficient solar energy absorbed during photosynthesis, which came to Earth, moving through living organisms. Ultimately, this circuit returns to the environment. natural environment in the form of low-efficiency thermal energy. Nutrients also move along it from producers to consumers and then to decomposers, and then back to producers.
Each link in the food chain is called a trophic level. The first trophic level is occupied by autotrophs, otherwise referred to as primary producers. Organisms of the second trophic level are called primary consumers, the third - secondary consumers, etc. Usually there are four or five trophic levels and rarely more than six (Fig. 1).
There are two main types of food chains - grazing (or "eating") and detrital (or "decaying").
Rice. 1. Food chains of biocenosis according to N.F. Reimers: generalized (a) and real (b)
The arrows in Figure 1 show the direction of energy movement, and the numbers show the relative amount of energy coming to the trophic level.
In grazing food chains, the first trophic level is occupied by green plants, the second by grazing animals (the term "grassland" covers all organisms that feed on plants), and the third by predators.
So, pasture food chains are:
PLANT MATERIAL (e.g. nectar) => FLY => SPIDER =>
=> SHREDDER => OWL
ROSE BUSH JUICE => APHIDS => LADYBUG => SPIDER =>
=> INSECTIVORUS BIRD => BIRD OF PREY.
The detrital food chain begins with detritus according to the scheme:
DETRIT-> DETRITOPHY -> PREDATOR
Typical detrital food chains are:
FOREST LITTER => EARTHWORM => BLACKDRUS =>
=> SPARROW HAWK
DEAD ANIMAL \u003d\u003e CARRIER FLY LARVIES \u003d\u003e GRASS FROG \u003d\u003e ORDINARY SNAIL.
The concept of food chains allows us to further trace the cycle chemical elements in nature, although simple food chains such as those depicted earlier, where each organism is represented as feeding on only one type of organism, are rare in nature.
Real food relationships are much more complex, because an animal can feed on organisms different types included in the same food chain or in different chains, which is especially characteristic of predators (consumers) of higher trophic levels. The relationship between pasture and detritus food chains is illustrated by the energy flow model proposed by Yu. Odum (Fig. 2).
Omnivorous animals (in particular, humans) feed on both consumers and producers. Thus, in nature, food chains intertwine, form food (trophic) networks.
Rice. 2. Scheme of pasture and detrital food chains (according to Yu. Odum)
Lindemann's rule (10%)
The through flow of energy, passing through the trophic levels of the biocenosis, is gradually extinguished. In 1942, R. Lindemann formulated the law of the pyramid of energies, or the law (rule) of 10%, according to which from one trophic level of the ecological pyramid it moves to another, higher level (along the "ladder": producer - consumer - decomposer) on average about 10% of the energy received at the previous level of the ecological pyramid. The reverse flow associated with the consumption of substances and the energy produced by the upper level of the ecological pyramid of energy by its lower levels, for example, from animals to plants, is much weaker - no more than 0.5% (even 0.25%) of its total flow, and therefore we can say about the cycle of energy in the biocenosis is not necessary.
If the energy during the transition to more high level ecological pyramid is lost tenfold, then the accumulation of a number of substances, including toxic and radioactive ones, increases in approximately the same proportion. This fact is fixed in the biological amplification rule. It is true for all cenoses. In aquatic biocenoses, the accumulation of many toxic substances, including organochlorine pesticides, correlates with the mass of fats (lipids), i.e. clearly has an energy background.
Food chains can be divided into two types. The pasture chain starts from a green plant and goes on to grazing herbivores and then to predators. Examples of grazing chains are shown in the illustrations in paragraph 4.2. The detrital chain comes from the dead organic matter(detritus) to decomposers and animals that eat dead remains (detritophages), and then to predators that feed on these animals and microbes. This figure shows an example of a detritus food chain from the tropics; this is a chain starting from the falling leaves of mangroves - trees and shrubs growing on sea coasts periodically flooded by tides and in estuaries. Their leaves fall into brackish waters overgrown with mangrove trees and are carried by the current across a vast area of bays. Mushrooms, bacteria and protozoa develop in the water on fallen leaves, which, together with the leaves, are eaten by numerous organisms: fish, molluscs, crabs, crustaceans, insect larvae and roundworms - nematodes. Small fish (for example, minnows) feed on these animals, and they, in turn, are eaten by big fish and predatory fish-eating birds. |
FOOD CHAIN(trophic chain, food chain), the relationship of organisms through the relationship of food - consumer (some serve as food for others). In this case, the transformation of matter and energy from producers(primary producers) through consumers(consumers) to decomposers(converters of dead organics into inorganic substances digestible by producers).
There are 2 types of food chains - pasture and detrital. The pasture chain starts from green plants, goes to grazing herbivorous animals (consumers of the 1st order) and then to predators that prey on these animals (depending on the place in the chain - consumers of the 2nd and subsequent orders). The detrital chain starts with detritus (a product of the decomposition of organic matter), goes to microorganisms that feed on it, and then to detritus feeders (animals and microorganisms involved in the process of decomposition of dying organic matter).
An example of a pasture chain is its multi-channel model in the African savannah. Primary producers are herbage and trees, consumers of the 1st order are herbivorous insects and herbivores (ungulates, elephants, rhinos, etc.), 2nd order - predatory insects, 3rd order - carnivorous reptiles (snakes, etc.), 4th - predatory mammals and birds of prey. In turn, detritivores (scarab beetles, hyenas, jackals, vultures, etc.) at each stage of the pasture chain destroy the carcasses of dead animals and the remains of predators' food. The number of individuals included in the food chain consistently decreases in each of its links (the rule of the ecological pyramid), i.e., the number of victims each time significantly exceeds the number of their consumers. Food chains are not isolated from each other, but are intertwined with each other, forming food webs.
The maintenance of the vital activity of organisms and the circulation of matter in ecosystems, i.e. the existence of ecosystems, depends on constant flow the energy necessary for all organisms for their vital activity and self-reproduction (Fig. 12.19).
Rice. 12.19. Energy flow in an ecosystem (according to F. Ramad, 1981)
Unlike substances that continuously circulate through different blocks of the ecosystem, which can always be reused, enter the cycle, energy can only be used once, i.e., there is a linear flow of energy through the ecosystem.
One-sided influx of energy as a universal phenomenon of nature occurs as a result of the laws of thermodynamics. First Law states that energy can change from one form (such as light) to another (such as the potential energy of food), but cannot be created or destroyed. Second law argues that there can be no process associated with the transformation of energy, without the loss of some of its part. A certain amount of energy in such transformations is dissipated into inaccessible thermal energy and hence is lost. Hence, there can be no transformations, for example, of food substances into the substance that makes up the body of an organism, going with 100 percent efficiency.
Thus, living organisms are energy converters. And every time energy is converted, some of it is lost as heat. Ultimately, all the energy entering the biotic cycle of the ecosystem is dissipated in the form of heat. Living organisms do not actually use heat as a source of energy to do work - they use light and chemical energy.
Food chains and webs, trophic levels
Within an ecosystem, energy-containing substances are created by autotrophic organisms and serve as food for heterotrophs. Food bonds are mechanisms for transferring energy from one organism to another.
A typical example: an animal eats plants. This animal, in turn, can be eaten by another animal. In this way, energy can be transferred through a number of organisms - each subsequent one feeds on the previous one, supplying it with raw materials and energy (Fig. 12.20).
Rice. 12.20. Biotic cycling: the food chain
(according to A. G. Bannikov et al., 1985)
This sequence of energy transfer is called food (trophic) chain, or power circuit. The place of each link in the food chain is trophic level. The first trophic level, as noted earlier, is occupied by autotrophs, or the so-called primary producers. Organisms in the second trophic level are called primary consumers, third - secondary consumers etc.
Generally, there are three types of food chains. The food chain of predators begins with plants and moves from small organisms to organisms of ever larger sizes. On land, food chains consist of three to four links.
One of the simplest food chains looks like (see Fig. 12.5):
plant ® hare ® wolf
producer ® herbivore ® carnivore
The following food chains are also widespread:
plant material (e.g. nectar) ® fly ® spider ®
shrew ® owl.
the juice rose bush® aphid ® ladybug ®
® spider ® insectivorous bird ® bird of prey.
- (brought in by the current - lake, sea; brought in by man - agricultural land, carried by wind or precipitation - plant remains on eroded mountain slopes).
The differences between an ecosystem and a biogeocenosis can be reduced to the following points:
1) biogeocenosis - a territorial concept, refers to specific areas of land and has certain boundaries that coincide with the boundaries of phytocenosis. Feature biogeocenosis, which N.V. Timofeev-Resovsky, A.N. Tyurukanov (1966) - not a single significant biocenotic, soil-geochemical, geomorphological and microclimatic boundary passes through the territory of biogeocenosis.
The concept of an ecosystem is broader than the concept of biogeocenosis; it is applicable to biological systems of varying complexity and size; ecosystems often do not have a certain volume and strict boundaries;
2) in biogeocenosis, organic matter is always produced by plants, therefore the main component of biogeocenosis is phytocenosis;
In ecosystems, organic matter is not always created by living organisms, it often comes from outside.
(brought in by the current - lake, sea; brought in by man - agricultural land, carried by wind or precipitation - plant remains on eroded mountain slopes).
3) biogeocenosis is potentially immortal;
The existence of an ecosystem can end with the cessation of the arrival of matter or energy into it.
4) an ecosystem can be both terrestrial and aquatic;
Biogeocenosis is always a terrestrial or shallow-water ecosystem.
5) - in the biogeocenosis there should always be a single edificator (edificatory grouping or synusia), which determines the whole life and structure of the system.
There may be several in an ecosystem.
On the early stages development of the slope ecosystem is the future forest cenosis. It consists of groupings of organisms with different edificators and rather heterogeneous environmental conditions. Only in the future, the same grouping can be influenced not only by its edifier, but also by the edifier of the cenosis. And the second will be the main one.
Thus, not every ecosystem is a biogeocenosis, but each biogeocenosis is an ecosystem, which fully corresponds to Tensley's definition.
Ecological structure of biogeocenosis
Each biogeocenosis is composed of certain ecological groups of organisms, the ratio of which reflects ecological structure communities that develop over a long period of time in certain climatic, soil and landscape conditions are strictly regular. For example, in biogeocenoses of different natural areas the ratio of phytophages (animals that feed on plants) and saprophages naturally changes. In steppe, semi-desert and desert regions, phytophages prevail over saprophages, while in forest communities, on the contrary, saprophagy is more developed. In the depths of the ocean, the main type of food is predation, while on the illuminated surface of the reservoir, filter feeders that consume phytoplankton or species with a mixed diet predominate.
Food webs within each biogeocenosis have a well-defined structure.
It is characterized by the number, size and total mass of organisms - biomass - at each level of the food chain. Pasture food chains are characterized by an increase in population density, reproduction rate and productivity of their biomass.
The decrease in biomass during the transition from one food level to another is due to the fact that not all food is assimilated by consumers.
So, for example, in a leaf-eating caterpillar, only half of the plant material, the rest is excreted in the form of excrement.
In addition, most of the nutrients absorbed by the intestines are used for respiration, and only 10-15% is ultimately used to build new caterpillar cells and tissues. For this reason, the production of organisms of each subsequent trophic level is always less (10 times on average) than the production of the previous one, i.e., the mass of each subsequent link in the food chain progressively decreases. This pattern is called the rule of the ecological pyramid.
There are three ways of compiling ecological pyramids:
- 1. The pyramid of numbers reflects the numerical ratio of individuals of different trophic levels of the ecosystem. If organisms within the same or different trophic levels differ greatly in size, then the pyramid of numbers gives distorted ideas about the true ratios of trophic levels. For example, in the plankton community, the number of producers is tens and hundreds of times more numbers consumers, and in the forest hundreds of thousands of consumers can feed on the organs of one tree - the producer;
- 2. The biomass pyramid shows the amount of living matter, or biomass, at each trophic level. In most terrestrial ecosystems, the biomass of producers, i.e., the total mass of plants, is the largest, and the biomass of organisms of each subsequent trophic level is less than the previous one. However, in some communities, the biomass of consumers of the first order is greater than the biomass of producers. For example, in the oceans, where the main producers are unicellular algae with a high reproduction rate, their annual production can exceed the biomass reserve by tens and even hundreds of times. At the same time, all the products formed by algae are so quickly involved in the food chain that the accumulation of algae biomass is small, but due to high reproduction rates, their small reserve is sufficient to maintain the rate of organic matter reproduction. In this regard, in the ocean, the biomass pyramid has an inverse relationship, i.e., “inverted”. At the highest trophic levels, the tendency to accumulate biomass prevails, since the life span of 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 body;
- 3. The pyramid of energy reflects the amount of energy flow in the food chain. The shape of this pyramid is not affected by the size of the individuals, and will always be triangular with a wide base at the bottom, as dictated by the second law of thermodynamics. Therefore, the pyramid of energy gives the most complete and accurate idea of the functional organization of the community, of all metabolic processes in the ecosystem. If the pyramids of numbers and biomass reflect the statics of the ecosystem (the number and biomass of organisms at a given moment), then the pyramid of energy reflects the dynamics of the passage of a mass of food through the food chain. Thus, the base in the pyramids of numbers and biomass can be larger or smaller than the subsequent trophic levels (depending on the ratio of producers and consumers in different ecosystems). The pyramid of energy always narrows upwards. This is due to the fact that the energy spent on respiration is not transferred to the next trophic level and leaves the ecosystem. Therefore, each subsequent level will always be less than the previous one. In terrestrial ecosystems, a decrease in the amount of available energy is usually accompanied by a decrease in the abundance and biomass of individuals at each trophic level. Due to such large energy losses for building new tissues and respiration of organisms, food chains cannot be long; they usually consist of 3-5 links (trophic levels).
An ecological pyramid is a graphic representation of energy losses in food chains.
Food chains are stable chains of interconnected species that consistently extract materials and energy from the original food substance that have developed during the evolution of living organisms and the biosphere as a whole. They make up the trophic structure of any biocenosis, through which energy transfer and substance cycling are carried out. The food chain consists of a series of trophic levels, the sequence of which corresponds to the flow of energy.
The primary source of energy in food chains is solar energy. The first trophic level - producers (green plants) - use solar energy in the process of photosynthesis, creating the primary production of any biocenosis. At the same time, only 0.1% of solar energy is used in the process of photosynthesis. The efficiency with which green plants assimilate solar energy is estimated by the value of primary productivity. More than half of the energy associated with photosynthesis is immediately consumed by plants in the process of respiration, the rest of the energy is transferred further along the food chains.
At the same time, there is an important regularity associated with the efficiency of the use and conversion of energy in the process of nutrition. Its essence is as follows: the amount of energy spent on maintaining one's own life activity in food chains grows from one trophic level to another, while productivity decreases.
Phytobiomass is used as a source of energy and material to create the biomass of organisms of the second
trophic level consumers of the first order - herbivores. Usually the productivity of the second trophic level is no more than 5 - 20% (10%) of the previous level. This is reflected in the ratio of plant and animal biomass on the planet. The volume of energy necessary to ensure the vital activity of the organism grows with an increase in the level of morphofunctional organization. Accordingly, the amount of biomass created at higher trophic levels is reduced.
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 ratios of primary and secondary production. Always quantity vegetable matter, which serves as the basis of the food chain, is several times (about 10 times) greater than the total mass of herbivorous animals, and the mass of each subsequent link in the food chain, respectively, changes proportionally.
The progressive decline of assimilated energy in a series of trophic levels is reflected in the structure of ecological pyramids.
A decrease in the amount of available energy at each subsequent trophic level is accompanied by a decrease in biomass and the number of individuals. Pyramids of biomass and abundance of organisms for a given biocenosis are repeated in in general terms productivity pyramid configuration.
Graphically, the ecological pyramid is depicted as several rectangles of the same height but different lengths. The length of the rectangle decreases from the bottom to the top, corresponding to a decrease in productivity at subsequent trophic levels. The lower triangle is the largest in length and corresponds to the first trophic level - producers, the second is approximately 10 times smaller and corresponds to the second trophic level - herbivorous animals, consumers of the first order, etc.
The rate of creation of organic matter does not determine its total reserves, i.e. the total mass of organisms at each trophic level. The available biomass of producers and 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, i.e., correlate with each other. how strong the consumption of the formed reserves is. An important role is played by the speed of reproduction of the main generations of producers and consumers.
In most terrestrial ecosystems, as already mentioned, the biomass rule also applies, i.e. the total mass of plants turns out to be greater than the biomass of all herbivores, and the mass of herbivores exceeds the mass of all predators.
It is necessary to distinguish quantitatively between productivity - namely, the annual growth of vegetation - and biomass. The difference between the primary production of the biocenosis and the biomass determines the extent of the grazing of the plant mass. Even for communities with a predominance of herbaceous forms, whose biomass reproduction rate is quite high, animals use up to 70% of the annual plant growth.
In those trophic chains where energy transfer is carried out through “predator-prey” connections, pyramids of the number of individuals are often observed: the total number of individuals participating in food chains decreases with each link. This is also due to the fact that predators, as a rule, are larger than their victims. An exception to the rules of the pyramid of numbers are cases when small predators live by group hunting for large animals.
All three rules of the pyramid - productivity, biomass and abundance - express energy relationships in ecosystems. At the same time, the productivity pyramid has a universal character, while the pyramids of biomass and abundance appear in communities with a certain trophic structure.
Knowledge of the laws of ecosystem productivity, 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 humans. Importance It also has secondary production of biocenoses, obtained from industrial and agricultural animals, as a source of animal protein. Knowledge of the laws of distribution of energy, flows of energy and matter in biocenoses, the laws of productivity of plants and animals, understanding the limits of permissible withdrawal of plant and animal biomass from natural systems allow us to correctly build relationships in the "society - nature" system.
Relationships in which some organisms eat other organisms or their remains or secretions (excrement) are called trophic (trophe - nutrition, food, gr.). At the same time, nutritional relationships between members of the ecosystem are expressed through trophic (food) chains . Examples of such circuits are:
Moss moss → deer → wolf (tundra ecosystem);
Grass → cow → human (anthropogenic ecosystem);
microscopic algae (phytoplankton) → bugs and daphnia (zooplankton) → roach → pike → gulls (aquatic ecosystem).
Influencing food chains with the aim of optimizing them and obtaining more or better products in quality is not always successful. So widely known from the literature is the example of the importation of cows to Australia. Prior to this, natural pastures were used mainly by kangaroos, whose excrement was successfully developed and processed by the Australian dung beetle. Cow dung was not used by the Australian beetle, as a result of which the gradual degradation of pastures began. To stop this process, the European dung beetle had to be brought to Australia.
Trophic or food chains can be represented in the form pyramids. 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 energy pyramid law R. Lindemann and ten percent rule , approximately 10% (from 7 to 17%) of energy or matter in energy terms passes from each stage to the next stage (Fig. 3.7). Note that at each subsequent level, with a decrease in the amount of energy, its quality increases, i.e. the ability to do the work of a unit of animal biomass is a corresponding number of times higher than the same plant biomass.
A striking example is the high seas food chain, represented by plankton and whales. The mass of plankton is dispersed in ocean water and, if the bioproductivity of the open sea is less than 0.5 g/m2 day-1, the amount of potential energy in cubic meter ocean water is infinitely small 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.
Fig.3.7. Pyramid of energy transfer along the food chain (according to Y. Odum)
In the destruction of organics, a corresponding sequence is also observed: for example, about 90% of the energy of pure primary production is released by microorganisms and fungi, less than 10% by invertebrates, and less than 1% by vertebrates, which are final cosuments. In accordance with the last digit, 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%.
Based on the food chain as the basis for the functioning of the ecosystem, it is also possible to explain the cases of accumulation in the tissues of certain substances (for example, synthetic poisons), which, as they move along the trophic chain, do not participate in the normal metabolism of organisms. According to biological amplification rules there is an approximately tenfold increase in the concentration of the pollutant when moving to a higher level of the ecological pyramid.
In particular, a seemingly insignificant elevated content of radionuclides in river water at the first level of the trophic chain is assimilated by microorganisms and plankton, then it is concentrated in fish tissues and reaches maximum values in gulls. Their eggs have a level of radionuclides 5000 times higher than background pollution.
The species composition of organisms is usually studied at the level populations .
Recall that a population is a set of individuals of the same species inhabiting the same territory, having a common gene pool and the ability to interbreed freely. In general, one or another population can be within a certain ecosystem, but it can also spread beyond the borders. For example, the population of the black-capped marmot of the Tuora-Sis ridge, listed in the Red Book, is known and protected. This population is not limited to this range, but also extends further south to the Verkhoyansk mountains in Yakutia.
The environment in which the species under study usually occurs is called its habitat.
As a rule, an ecological niche is occupied by one species or its population. With the same requirements for environment and food resources, two species invariably enter into a competitive struggle, which usually ends in the displacement of one of them. This situation is known in systems ecology as G.F. principle Gause , which states that two species cannot exist in the same locality if their ecological needs are identical, i.e. if they occupy the same niche. Accordingly, the system of interacting, differentiated by ecological niche populations, complementing each other to a greater extent than competing with each other for the use of space, time and resources, is called a community (coenosis).
The polar bear cannot live in taiga ecosystems, just like the brown bear in the polar regions.
Speciation is always adaptive, so Ch. Darwin's axiom each species is adapted to a strictly defined set of conditions of existence specific to it. At the same time, organisms reproduce with an intensity that provides the maximum possible number of them ( rule of maximum "life pressure"" ).
For example, organisms of oceanic plankton quite quickly cover an area of thousands of square kilometers in the form of a film. V.I.Vernadsky calculated that the speed of Fischer bacterium with the size of 10-12 cm3 by reproduction in a straight line would be equal to about 397,200 m/h - the speed of an airplane! However, excessive reproduction of organisms is limited by limiting factors and correlates with the amount of food resources of their habitat.
When species disappear, primarily composed of large individuals, as a result, the material-energy structure of qualifications changes. If the energy flow passing through the ecosystem does not change, then the mechanisms ecological duplication according to the principle: an endangered or destroyed species within one level of the ecological pyramid replaces another functional-coenotic, similar one. The substitution of a species proceeds according to the scheme: a small one replaces a large one, evolutionarily lower organized, more highly organized, more genetically labile, less genetically variable. As ecological niche cannot be empty in the biocenosis, then ecological duplication occurs necessarily.
A successive change of biocenoses, successively arising in the same territory under the influence of natural factors or human impact, is called succession (succession - continuity, lat.). For example, after a forest fire, for many years the burnt area is first populated with grasses, then with shrubs, then with deciduous trees, and finally with coniferous forests. In this case, successive communities that replace each other are called series or stages. The end result of succession will be the state of a stabilized ecosystem - menopause (climax - stairs, "mature step", gr.).
A succession that begins in a previously unoccupied area is called primary . These include lichen settlements on stones, which will later replace mosses, grasses and shrubs (Fig. 3.8). If a community develops on the site of an already existing one (for example, after a fire or uprooting, a pond or reservoir device), then they talk about secondary successions. Of course, succession rates will vary. Primary successions may take hundreds or thousands of years, while secondary successions are faster.
All populations of producers, consumers and heterotrophs closely interact through trophic chains and thus maintain the structure and integrity of biocenoses, coordinate the flows of energy and matter, and determine the regulation of their environment. The whole set of bodies of living organisms inhabiting the Earth is physically and chemically one, regardless of their systematic affiliation, and is called living matter ( the law of physico-chemical unity of living matter by V.I. Vernadsky). The mass of living matter is relatively small and is estimated at 2.4-3.6 * 1012 tons (in dry weight). If it is distributed over the entire surface of the planet, you get a layer of only one and a half centimeters. According to VI Vernadsky, this "film of life", which is less than 10-6 masses of other shells of the Earth, is "one of the most powerful geochemical forces of our planet."
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