Food chains in a reservoir as a sustainable ecosystem. Food chains and food webs in water bodies Types of food chains

trophic structure. The species that make up the ecosystem are interconnected by food ties, as they serve as food objects for each other.

in the pond producers are green algae. They are eaten by small herbivorous crustaceans (daphnia, cyclops) - consumers (consumers) of the first order. These animals are eaten by carnivorous larvae of various aquatic insects (for example, dragonflies) - this is consumers (consumers) of the second order. Small fish (for example, roach) feed on larvae - consumers (consumers) of the third order. And the fish become the prey of the pike - consumer (consumer) of the fourth order. Such a sequence of organisms feeding on each other is called a food, or trophic, chain. Individual links of the trophic chain are called trophic levels.
There are two types of trophic (food) chains. Food chains that start with plants and go through herbivores to other consumers are called pasture or chains eating. Food chains of another type start with dead plants, carcasses, or animal droppings and move on to small animals and micro-organisms. These chains are called detritus, or chains decomposition.

Linear food chains are a rarity in nature. As a rule, food chains in an ecosystem are closely intertwined. The totality of food links in an ecosystem forms food webs, in which many consumers serve as food for several members of the ecosystem.

Despite the outward simplicity of a freshwater body of water, its trophic structure (the system of food relations) is quite complex. Higher plants feed on insect larvae, amphibians, scraping gastropods, herbivorous fish. Numerous protozoa (flagellates, ciliates, naked and testate amoebae), lower crustaceans (daphnia, cyclops), filtering bivalve mollusks, insect larvae (mayflies, dragonflies, caddisflies) eat unicellular and multicellular algae.

Crustaceans, worms, insect larvae serve as food for fish and amphibians (frogs, newts). Predatory fish (perch) hunt for herbivores (crucian carp), and large predators (pike) - for smaller ones. Mammals (desman, beavers, otters) also find their food: they eat fish, mollusks, insects and their larvae.

Organic residues settle to the bottom, bacteria develop on them, consumed by protozoa and filter mollusks. Bacteria, flagellates and water sports fungi decompose organic matter into inorganic compounds, reused by plants and algae.

Cause underdevelopment life in some bodies of water is low level mineral content (compounds of phosphorus, nitrogen, etc.) or unfavorable acidity of water. The introduction of mineral fertilizers and the normalization of acidity by liming promotes the development of freshwater plankton - a complex of small organisms suspended in water (microscopic algae, bacteria and their consumers: ciliates, crustaceans, etc.). Plankton, being the base of the food pyramid, feeds various animals consumed by fish. As a result of restoration measures, productivity fisheries increases significantly.

On deployment in the space of the food chains of the reservoir, a technology for processing animal waste has been developed. Manure is washed off into settling tanks, where it serves as food for numerous unicellular algae, the water "blooms". Algae, together with water in small doses, is transferred to another reservoir, where they are eaten by daphnia and other filter-feeding crustaceans. In the third pond, fish are grown on crustaceans. Pure water is reused on farms, excess crustaceans are used for protein feed for livestock, and fish are consumed by humans.

44. The concept of stability, sustainability and endurance of aquatic ecosystems
The problem of stability and sustainability of ecosystems and their communities of organisms is one of the most important in modern ecology. It is actively discussed, and by now the literature has accumulated enough a large number of different, often conflicting ideas about the stability and resilience of ecosystems. For example, it is believed that only stable ecosystems can exist for a long time and the limits of their stability are determined by the maximum loads that they can withstand without being disturbed. Some authors consider stability and stability as synonyms (Odum, 1986, Nedorezov, Sidko, 1995), while others use them to describe different states of ecosystems. Let's consider some of the most common ideas about these important properties of biological systems and ecosystems.

Main points:

1. The stability of ecosystems arises as a result of internal interactions, it requires intraspecific relationships, while interspecific interactions lead to destabilizing influences and are a measure of system variability.

2. More complex organized systems are more stable. The complexity of the structure of communities of organisms, estimated by their diversity: the more diverse the system, the more stable it is. Such systems are controlled by biotic factors. Under the influence of anthropogenic factors and euthophytization of water bodies, the diversity and stability of systems decrease.

3. The stability of ecosystems can be short-term (successional) and long-term (evolutionary).

4. Stability is considered as the ability of a system to maintain a relatively unchanged state under the influence of non-catastrophic phenomena and to resist changes (abiotic and biotic influences environment), maintaining dynamic balance (homeostasis).

5. The structure of systems that are not subject to anthropogenic impacts changes over time depending on changes in external and internal factors. These are evolutionary processes. Thus, in the process of evolution of lakes, gradual changes in the structure and functioning of their ecosystems occur.

6. Each ecosystem and its constituent communities of organisms are adapted to seasonal, annual changes in factors external environment. This is expressed in fluctuations in the values ​​of their structural and functional characteristics, such as species composition, diversity, biomass, abundance, production, exchange costs, relative to some average values ​​over these time periods. Therefore, usually communities of benthic or planktonic organisms in different types and geographic location reservoirs or streams are characterized by annual or growing season average values ​​of biomass or abundance. The maintenance of this average level, species composition and diversity reflects the stability of the ecosystem over time.

7. The stability of communities and ecosystems is directly dependent on the transparency of water in reservoirs. This is of fundamental importance, since the primary production of plankton is inversely related to water transparency. Thus, with an increase in the productivity or degree of eutrophication of water bodies or streams, the stability of ecosystems and their components decreases.

The stability of hydrobiont communities and ecosystems also changes with a change in the degree of their exploitation. Thus, an increase in the pressure of fish in nursery lakes led to a decrease in the stability of plankton and benthic communities.

8. Taking into account all the above, there is no reason to talk about stable and unstable ecosystems. An ecosystem is in a stable state as long as specific environmental factors act on it with constant force. It is characterized by specific structural and functional characteristics, sustainability.

In communities of aquatic organisms, during the year or the growing season, due to seasonal cycles of development of organisms, a change in the types of dominants can occur, therefore, it is more reliable to determine the stability of the system by the average values ​​of structural and functional characteristics for the season or year.

The energy contained in the organic matter of some organisms is consumed by other organisms. The transfer of substances and the energy contained in them from autotrophs to heterotrophs, which occurs as a result of eating one organism by another, is called food chain (food chain, trophic chain).

The energy of the sun plays a huge role in the reproduction of life. The amount of this energy is very high (about 55 kcal per 1 cm2 per year). Of this amount, producers - green plants - as a result of photosynthesis fix no more than 1-2% of energy, and deserts and the ocean - hundredths of a percent.

The number of links in the food chain may be different, but usually there are 3-4 (rarely 5). The fact is that so little energy is supplied to the final link of the food chain that it will not be enough if the number of organisms increases.

Organisms at each trophic level are adapted by nature to consume a certain type of food, which is the organisms of the previous trophic level (or several previous levels).

The simplest food chain(or food chain) may consist of phytoplankton, then larger herbivorous planktonic crustaceans (zooplankton), and the chain ends with a whale (or small predators) that filter these crustaceans from the water.

All elements of nature, living and non-living, are one whole, a complex of interacting and interconnected phenomena and beings adapted to each other. These are links in the same chain. And if at least one such link is removed from the general chain, the results may be unexpected.

Food chains can be divided into two main types: pasture and detritus. Food prices that begin with autotrophic photosynthetic organisms are called grazing chains, or grazing chains. At the top of the pasture chain are green plants. Phytophages are usually found at the second level of the pasture chain; animals that eat plants. An example of a pasture food chain is the relationship between organisms in a floodplain meadow. Such a chain begins with a meadow flowering plant. The next link is a butterfly that feeds on the nectar of a flower. Then comes the inhabitant of wet habitats - the frog. Her protective coloring allows her to lie in wait for the victim, but does not save her from another predator - an ordinary grass snake. The heron, having caught the snake, closes the food chain in the floodplain meadow.

If the food chain begins with dead plant remains, corpses and animal excrement - detritus, it is called detrital, or chain of decomposition. The term "detritus" means a decay product. It is borrowed from geology, where the products of the destruction of rocks are called detritus. In ecology, detritus is organic matter involved in the decomposition process. Such chains are characteristic of the communities of the bottom of deep lakes and oceans, where many organisms feed on detritus formed by dead organisms from the upper illuminated layers of the reservoir.

In contrast to the pasture chain, the size of organisms does not increase when moving along the detrital chain, but, on the contrary, decreases. So, gravedigger insects can stand on the second level. But the most typical representatives of the detrital chain are fungi and microorganisms that feed on dead matter and complete the process of bioorganic decomposition to the state of the simplest mineral and organic substances, which are then consumed in dissolved form by the roots of green plants at the top of the pasture chain, thereby starting a new circle of movement of matter.

In some ecosystems, pasture chains predominate, in others - detrital chains. For example, a forest is considered an ecosystem dominated by detrital chains. In the rotting stump ecosystem, there is no grazing chain at all. At the same time, for example, in the ecosystems of the sea surface, almost all producers represented by phytoplankton are consumed by animals, and their corpses sink to the bottom, i.e. leave the published ecosystem. These ecosystems are dominated by grazing or grazing food chains.

The general rule for any food chain is that at each trophic level of a community, most of the energy ingested in food is expended in sustaining life, dissipated, and can no longer be used by other organisms. Thus, the food consumed at each trophic level is not fully assimilated. A significant part of it is spent on metabolism. With the transition to each subsequent link in the food chain, the total amount of usable energy transferred to the next higher trophic level decreases.

In ecosystems, producers, consumers and decomposers are united by complex processes of the transfer of substances and energy, which is contained in food, created mainly by plants.

The transfer of the potential energy of food created by plants through a number of organisms by eating some species by others is called a trophic (food) chain, and each link is called a trophic level.

All organisms that eat the same type of food belong to the same trophic level.

In Fig.4. a diagram of the trophic chain is presented.

Fig.4. Food chain diagram.

Fig.4. Food chain diagram.

First trophic level form producers (green plants) that accumulate solar energy and create organic substances in the process of photosynthesis.

At the same time, more than half of the energy stored in organic substances is consumed in the life processes of plants, turning into heat and dissipating in space, and the rest enters the food chain and can be used by heterotrophic organisms of subsequent trophic levels when feeding.

Second trophic level form consumers of the 1st order - these are herbivorous organisms (phytophages) that feed on producers.

Consumers of the first order spend most of the energy contained in food to ensure their life processes, and use the rest of the energy to build their own body, thereby transforming plant tissues into animals.

Thus , consumers of the 1st order carry out the first, fundamental stage in the transformation of organic matter synthesized by producers.

Primary consumers can serve as a source of nutrition for consumers of the 2nd order.

Third trophic level form consumers of the 2nd order - these are carnivorous organisms (zoophages), which feed exclusively on herbivorous organisms (phytophages).

Consumers of the 2nd order carry out the second stage of the transformation of organic matter in food chains.

However, the chemicals that make up the tissues of animal organisms are quite homogeneous and therefore the transformation of organic matter during the transition from the second trophic level of consumers to the third is not as fundamental as when moving from the first trophic level to the second, where plant tissues are transformed into animals.

Secondary consumers can serve as a source of nutrition for consumers of the 3rd order.

Fourth trophic level form consumers of the 3rd order - these are carnivores that feed only on carnivorous organisms.

Last level of the food chain are occupied by decomposers (destructors and detritophages).

decomposers-destructors (bacteria, fungi, protozoa) in the course of their life activity decompose the organic remains of all trophic levels of producers and consumers to mineral substances, which again return to the producers.

All links in the food chain are interconnected and interdependent.

Between them, from the first to the last link, the transfer of substances and energy is carried out. However, it should be noted that when energy is transferred from one trophic level to another, it is lost. As a result, the food chain cannot be long and most often consists of 4-6 links.

However, such food chains pure form they are not usually found in nature, since each organism has several food sources, i.e. eats several types of food, and is itself used as food by numerous other organisms from the same food chain or even from different food chains.

For example:

omnivorous organisms eat both producers and consumers, i.e. are at the same time consumers of the first, second, and sometimes third order;

the mosquito, which feeds on the blood of humans and predatory animals, is at a very high trophic level. But mosquitoes feed on the swamp sundew plant, which, thus, is both a producer and a consumer of a high order.

Therefore, almost any organism that is part of one trophic chain can simultaneously be part of other trophic chains.

Thus, trophic chains can branch and intertwine many times, forming complex food webs or trophic (food) webs in which the multiplicity and diversity of food relationships acts as an important mechanism for maintaining the integrity and functional stability of ecosystems.

In Fig.5. a simplified diagram of a food network for a terrestrial ecosystem is shown.

Human intervention in the natural communities of organisms, through the intentional or unintentional elimination of a species, often has unpredictable Negative consequences and leads to a violation of the stability of ecosystems.

Fig.5. Food web diagram.

There are two main types of food chains:

grazing chains (grazing chains or or consumption chains);

detritus chains (decomposition chains).

Pasture chains (grazing chains or consumption chains) are the processes of synthesis and transformation of organic substances in trophic chains.

Pasture chains start with producers. Living plants are eaten by phytophages (first-order consumers), and phytophages themselves are food for carnivores (second-order consumers), which third-order consumers can eat, etc.

Examples of grazing chains for terrestrial ecosystems:

3 links: aspen → hare → fox; plant → sheep → human.

4 links: plants → grasshoppers → lizards → hawk;

plant flower nectar → fly → insectivorous bird →

predatory bird.

5 links: plants → grasshoppers → frogs → snakes → eagle.

Examples of grazing chains for aquatic ecosystems: →

3 links: phytoplankton → zooplankton → fish;

5 links: phytoplankton → zooplankton → fish → predatory fish →

predator birds.

Detrital chains (decomposition chains) are processes of gradual destruction and mineralization of organic substances in trophic chains.

Detrital chains begin with the gradual destruction of dead organic matter by detritivores, which sequentially replace each other in accordance with a specific type of nutrition.

At the last stages of degradation processes, reducers-destructors function, mineralizing the remains of organic compounds to simple inorganic substances, which are again used by producers.

For example, during the decomposition of dead wood, successively replace each other: beetles → woodpeckers → ants and termites → destructor fungi.

Detrital chains are most common in forests, where most (about 90%) of the annual increase in plant biomass is not consumed directly by herbivorous animals, but dies off and enters these chains in the form of leaf litter, then being decomposed and mineralized.

In aquatic ecosystems, most of the matter and energy is included in pasture chains, and in terrestrial ecosystems, detrital chains are of the greatest importance.

Thus, at the level of consumers, the flow of organic matter is divided into different groups of consumers:

living organic matter follows pasture chains;

dead organic matter goes along detrital chains.

Nutrition plays an important role in any ecosystem. Food is a source of energy for the continuation of the life processes of organisms. Accordingly, in each ecological system they are formed. If we give them a definition, we get the following: a trophic or food chain is the relationship between animals, plants, microorganisms on the principle of "food - consumer".

The structure is very simple. Representatives of the next link eat the organisms of the previous link. As a rule, the number of links reaches 3-4, and only very rarely - 5. Food chains in a reservoir, especially in freshwater, completely fall under trophic and can be of two types.

Types of food chains

Pasture food chains in the reservoir are typical for the upper layers, and detrital - for the bottom. But it is impossible to clearly separate them - they, like everything in nature, are interconnected. But whatever chains are present in an ecosystem, there are general rule. Each (link) spends most of the energy that is absorbed with food to maintain normal life.

Food chains in the pond. Examples

In any body of water, it is easy to give an example of the simplest food chain. Consider Baikal. Due to the diversity of flora and fauna, food chains in the reservoir are represented by several species. Since they are interrelated, some components of one can be replaced by elements from the other. Lake Baikal is divided into two - epipelegial and bathypeligial. The first prevails at the coastal level and in areas of mixing of water layers, the second is inherent in the near-bottom zone.

Producers (primary link) are different kinds algae. epishura appears. This species of planktonic crustaceans is the main consumer of phytoplankton and algae and is a zooplankton. Epishura serves as food for the next link - consumers of the second order. This group includes macrohectopus (zooplankton) and omul at all stages of development. But if the fish consume only the primary consumers, then the macrogetopus also consumes the producers. In turn, these crustaceans serve as food for omul, gobies, golomyanok and other fish. The final link is the seal, which consumes representatives of the previous level.

Detrital food chains

Any lake, pond or sea has a different depth in different parts of the occupied area. Detrital food chains in the reservoir prevail in the water column into which sunlight does not penetrate. Organic residues of plant and animal origin act as a producer. The first-order consumers are crustaceans and bacteria. The same detritivores often become food for consumers of the first and second order of the trophic food chain.

Variation in ecosystems

It is almost impossible to find a body of water, salt or fresh water, in which each link in the food chain would be represented by only one species of animal or plant. Such an ecosystem is doomed to extinction, since the absence of one element leads to an interruption in the food chain in the reservoir. If each link is filled with several species of animals or plants, then such a system is stable, since the absence of one or another component is replaced or supplemented by another. The annual populations each year are different quantity individuals. And only thanks to the diversity of species does not interrupt the food chain and destroy the ecosystem.

organic molecules, synthesized by autotrophs, serve as a source of nutrition (substance and energy) for heterotrophic animals. These animals, in turn, are eaten by other animals, and in this way energy is transferred through a series of organisms, where each subsequent one feeds on the previous one. Such a sequence is called a food chain, and each link in the chain corresponds to a certain trophic level (from the Greek troph - food). The first trophic level is always made up of autotrophs, called producers (from Latin producere - to produce). The second level is herbivores (phytophages), which are called consumers (from Latin consumo - “I devour”) of the first order; the third level (for example, predators) - second-order consumers, etc.

Usually in an ecosystem happens 4-5 trophic levels and rarely more than 6. This is partly due to the fact that at each of the levels part of the substance and energy is lost (incomplete eating of food, respiration of consumers, "natural" death of organisms, etc.); such losses are reflected in the figure and are discussed in more detail in the corresponding article. However, according to recent studies, the length of food chains is limited by other factors. It is possible that the availability of preferred food and territorial behavior play a significant role, which reduces the population density of organisms, and, hence, the number of higher-order consumers in a particular habitat. According to existing estimates, up to 80% of primary production in some ecosystems is not consumed by phytophages. Dead plant material becomes prey for organisms that feed on detritus (detritivores) or decomposers (destructors). In this case, we speak of detrital food chains. Detrital food chains dominate, for example, in tropical rainforests.

Producers

Almost all producers- photoautotrophs, i.e. green plants, algae and some prokaryotes, such as cyanobacteria (formerly called blue-green algae). The role of chemoautotrophs on the scale of the biosphere is negligible. Microscopic algae and cyanobacteria that make up phytoplankton are the main producers of aquatic ecosystems. On the contrary, at the first trophic level of terrestrial ecosystems, large plants predominate, for example, trees in forests, grasses in savannahs, steppes, fields, etc.

Consumers of the first order

On land, the main phytophages- insects, reptiles, birds and mammals. in fresh and sea ​​water these are usually small crustaceans (daphnia, sea acorns, crab larvae, etc.) and bivalves; most of them are filterers, straining out producers, as described in the corresponding article. Together with protozoa, many of them are part of zooplankton - a collection of microscopic drifting heterotrophs that feed on phytoplankton. The life of oceans and lakes is almost entirely dependent on planktonic organisms, which are in fact the beginning of all food chains in these ecosystems.

Consumers of the second, third and subsequent orders

Second order consumers they eat phytophages, that is, they are carnivores. Consumers of the third order and consumers of higher orders are also carnivores. These consumers can be divided into several ecological groups:

Here are two examples based on food chain photosynthesis:

Plant (leaves) -> Slug - "Frog -" Already - * - "Emine

Plant (phloem sap) -» Aphid -> Ladybug-> -» Spider -^ Starling -> Hawk