The food chain is the sequential transformation of elements of inorganic nature (biogenic, etc.) with the help of plants and light into organic substances (primary production), and the latter - by animal organisms at subsequent trophic (food) links (steps) into their biomass.

The food chain begins with solar energy, and each link in the chain represents a change in energy. All food chains in a community form trophic relationships.

There are various connections between the components of an ecosystem, and first of all they are connected together by the flow of energy and the circulation of matter. The channels through which energy flows through a community are called food circuits. Energy sunbeam falling on the tops of trees or on the surface of a pond is caught by green plants - whether huge trees or tiny algae - and is used by them in the process of photosynthesis. This energy goes into the growth, development and reproduction of plants. Plants, as producers of organic matter, are called producers. The producers, in turn, provide a source of energy for those who eat the plants and, ultimately, for the entire community.

The first consumers of organic matter are herbivorous animals - consumers of the first order. Predators that eat herbivorous prey act as second-order consumers. When moving from one link to another, energy is inevitably lost, so in food chain there are rarely more than 5-6 participants. Decomposers complete the cycle - bacteria and fungi decompose animal corpses and plant remains, converting organic matter into minerals, which are again absorbed by producers.

The food chain includes all plants and animals, as well as the chemical elements contained in water necessary for photosynthesis. A food chain is a coherent linear structure of links, each of which is connected to neighboring links by “food-consumer” relationships. Groups of organisms, for example, specific biological species, act as links in the chain. In water, the food chain begins with the smallest plant organisms- algae living in the euphotic zone and using solar energy for the synthesis of organic substances from inorganic chemical nutrients and carbonic acid dissolved in water. In the process of transferring the energy of food from its source - plants - through a number of organisms, which occurs by eating some organisms by others, there is a dissipation of energy, part of which turns into heat. With each successive transition from one trophic link (stage) to another, up to 80-90% of potential energy is lost. This limits the possible number of steps, or links in the chain, to usually four or five. The shorter the food chain, the more available energy is stored.

On average, 1 thousand kg of plants produces 100 kg of the body of herbivores. Predators that eat herbivores can build 10 kg of their biomass from this amount, and secondary predators only 1 kg. For example, a person eats big fish. Its food consists of small fish that consume zooplankton, which lives off of phytoplankton that capture solar energy.

Thus, to build 1 kg of a human body, 10 thousand kg of phytoplankton are required. Consequently, the mass of each subsequent link in the chain progressively decreases. This pattern is called the rule ecological pyramid. There is a pyramid of numbers, reflecting the number of individuals at each stage of the food chain, a pyramid of biomass - the amount of organic matter synthesized at each level, and a pyramid of energy - the amount of energy in food. They all have the same focus, differing in the absolute value of the digital values. In real conditions, power chains may have a different number of links. In addition, power circuits can intersect to form power networks. Almost all species of animals, with the exception of very specialized ones in terms of nutrition, use not one food source, but several). The greater the species diversity in a biocenosis, the more stable it is. So, in the plant-hare-fox food chain there are only three links. But the fox eats not only hares, but also mice and birds. The general pattern is that there are always green plants at the beginning of the food chain, and predators at the end. With each link in the chain, organisms become larger, they reproduce more slowly, and their number decreases. Species occupying the position of lower links, although provided with food, are themselves intensively consumed (mice, for example, are exterminated by foxes, wolves, owls). Selection goes in the direction of increasing fertility. Such organisms turn into a food source for higher animals without any prospects for progressive evolution.

In any geological epoch, organisms standing at the highest speed evolved top level in food relationships, for example, in the Devonian - lobe fishes - piscivorous predators; in the Carboniferous period - predatory stegocephalians. In Permian - reptiles that hunted stegocephalians. Throughout the Mesozoic era, mammals were exterminated by predatory reptiles and only as a result of the extinction of the latter at the end of the Mesozoic did they occupy a dominant position, giving large number forms

Food relationships are the most important, but not the only type of relationships between species in a biocenosis. One species can influence another in different ways. Organisms can settle on the surface or inside the body of individuals of another species, can form a habitat for one or several species, and influence air movement, temperature, and illumination of the surrounding space. Examples of connections affecting species habitats are numerous. Sea acorns are marine crustaceans that lead a sessile lifestyle and often settle on the skin of whales. The larvae of many flies live in cow dung. A particularly important role in creating or changing the environment for other organisms belongs to plants. In thickets of plants, be it a forest or a meadow, the temperature fluctuates less than in open spaces, and the humidity is higher.
Often one species participates in the spread of another. Animals carry seeds, spores, pollen, and other smaller animals. Plant seeds can be captured by animals upon accidental contact, especially if the seeds or infructescences have special hooks (string, burdock). When eating fruits and berries that cannot be digested, the seeds are released along with the droppings. Mammals, birds and insects carry numerous mites on their bodies.

All these diverse connections provide the possibility of the existence of species in a biocenosis, keep them close to each other, turning them into stable self-regulating communities.

A connection between two links is established if one group of organisms acts as food for another group. The first link in the chain has no predecessor, that is, organisms from this group do not use other organisms as food, being producers. Most often, plants, mushrooms, and algae are found in this place. Organisms in the last link in the chain do not act as food for other organisms.

Each organism has a certain amount of energy, that is, we can say that each link in the chain has its own potential energy. During the feeding process, the potential energy of food is transferred to its consumer.

All species that form the food chain exist on organic matter created by green plants. In this case, there is an important pattern associated with the efficiency of use and conversion of energy in the nutrition process. Its essence is as follows.

In total, only about 1% of the radiant energy of the Sun falling on a plant is converted into potential energy of chemical bonds of synthesized organic substances and can be further used by heterotrophic organisms for nutrition. When an animal eats a plant, most of the energy contained in the food is spent on various vital processes, turning into heat and dissipating. Only 5-20% of food energy passes into the newly built substance of the animal’s body. If a predator eats a herbivore, then again most of the energy contained in the food is lost. Due to such large losses of useful energy, food chains cannot be very long: they usually consist of no more than 3-5 links (food levels).

The amount of plant matter that serves as the basis of the food chain is always several times greater than the total mass of herbivorous animals, and the mass of each of the subsequent links in the food chain also decreases. This very important pattern is called the rule of the ecological pyramid.

When transferring potential energy from link to link, up to 80-90% is lost in the form of heat. This fact limits the length of the food chain, which in nature usually does not exceed 4-5 links. The longer the trophic chain, the lower the production of its last link in relation to the production of the initial one.

In Baikal, the food chain in the pelagic zone consists of five links: algae - epishura - macrohectopus - fish - seal or predatory fish(lenok, taimen, adult omul, etc.). Man participates in this chain as the last link, but he can consume products from lower links, for example, fish or even invertebrates when using crustaceans as food, aquatic plants etc. Short trophic chains are less stable and subject to greater fluctuations than long and complex ones in structure.

2. LEVELS AND STRUCTURAL ELEMENTS OF THE FOOD CHAIN

Usually, for each link in the chain, you can specify not one, but several other links connected to it by the “food-consumer” relationship. So not only cows, but also other animals eat grass, and cows are food not only for humans. The establishment of such connections turns the food chain into a more complex structure - food web.

In some cases, in a trophic network, it is possible to group individual links into levels in such a way that links at one level act only as food for the next level. This grouping is called trophic levels.

The initial level (link) of any trophic (food) chain in a reservoir is plants (algae). Plants do not eat anyone (with the exception of a small number of species of insectivorous plants - sundew, butterwort, bladderwort, nepenthes and some others); on the contrary, they are the source of life for all animal organisms. Therefore, the first step in the chain of predators are herbivores (grazing) animals. Following them are small carnivores that feed on herbivores, then a link of larger predators. In the chain, each subsequent organism is larger than the previous one. Predator chains contribute to the stability of the food chain.

The food chain of saprophytes is the final link in the trophic chain. Saprophytes feed on dead organisms. Chemicals, formed during the decomposition of dead organisms, are again consumed by plants - producer organisms, from which all trophic chains begin.

3. TYPES OF TROPHIC CHAINS

There are several classifications of trophic chains.

According to the first classification, there are three trophic chains in Nature (trophic means determined by Nature for destruction).

The first trophic chain includes the following free-living organisms:

herbivores;


predators - carnivores;


omnivores, including humans.


The basic principle of the food chain: “Who eats whom?”


The second trophic chain unites living things that metabolize everything and everyone. This task is performed by decomposers. They bring the complex substances of dead organisms to simple substances. The property of the biosphere is that all representatives of the biosphere are mortal. The biological task of decomposers is to decompose the dead.


According to the second classification, there are two main types of trophic chains - pasture and detrital.


In the pasture trophic chain (grazing chain), the basis is made up of autotrophic organisms, then there are herbivorous animals consuming them (for example, zooplankton feeding on phytoplankton), then predators (consumers) of the 1st order (for example, fish consuming zooplankton), predators of the 2nd order order (for example, pike perch feeding on other fish). The trophic chains are especially long in the ocean, where many species (for example, tuna) occupy the place of fourth-order consumers.


In detrital trophic chains (decomposition chains), most common in forests, most plant production is not consumed directly by herbivores, but dies, then undergoes decomposition by saprotrophic organisms and mineralization. Thus, detrital trophic chains start from detritus, go to microorganisms that feed on it, and then to detritivores and to their consumers - predators. In aquatic ecosystems (especially in eutrophic reservoirs and at great depths of the ocean), this means that part of the production of plants and animals also enters detrital trophic chains.


CONCLUSION


All living organisms inhabiting our planet do not exist on their own; they depend on the environment and experience its influence. This is a precisely coordinated complex of many environmental factors, and the adaptation of living organisms to them determines the possibility of the existence of all kinds of forms of organisms and the most varied formation of their life.


The main function of the biosphere is to ensure the circulation chemical elements, which is expressed in the circulation of substances between the atmosphere, soil, hydrosphere and living organisms.


All living beings are objects of food for others, i.e. interconnected by energy relationships. Food connections in communities, these are mechanisms for transferring energy from one organism to another. In every community trophic connections are intertwined in a complex net.


Organisms of any species are potential food for many other species


trophic networks in biocenoses are very complex, and it seems that the energy entering them can migrate for a long time from one organism to another. In fact, the path of each specific portion of energy accumulated by green plants is short; it can be transmitted through no more than 4-6 links in a series consisting of organisms sequentially feeding on each other. Such series, in which it is possible to trace the ways in which the initial dose of energy is spent, are called food chains. The location of each link in the food chain is called a trophic level. The first trophic level is always producers, creators of organic mass; plant consumers belong to the second trophic level; carnivores, living off herbivorous forms - to the third; consuming other carnivores - to the fourth, etc. Thus, consumers of the first, second and third orders are distinguished, occupying different levels in power circuits. Naturally, the food specialization of consumers plays a major role in this. Species with a wide range of nutrition are included in food chains at different trophic levels.


REFERENCES

1. Akimova T.A., Khaskin V.V. Ecology. Tutorial. – M.: DONITI, 2005.
   

   Moiseev A.N. Ecology in modern world// Energy. 2003. No. 4.
   

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Objective of the lesson: To form knowledge about the constituent components of a biological community, about the features of the trophic structure of the community, about food connections that reflect the path of substance circulation, to form the concepts of food chain, food web.

Lesson progress

1. Organizational moment.

2. Checking and updating knowledge on the topic “Composition and structure of the community.”

On the board: Our world is not an accident, not chaos - there is a system in everything.

Question. What system in living nature is this statement talking about?

Working with terms.

Exercise. Fill in the missing words.

Community of organisms different types closely interconnected are called …………. . It consists of: plants, animals, …………. , …………. . A collection of living organisms and components inanimate nature, united by the exchange of matter and energy on a homogeneous area of ​​the earth's surface are called …………….. or …………….

Exercise. Select four components of the ecosystem: bacteria, animals, consumers, fungi, abiotic component, climate, decomposers, plants, producers, water.

Question. How are living organisms connected to each other in an ecosystem?

3. Studying new material. Explain using presentation.

4. Consolidation of new material.

Task No. 1. Slide No. 20.

Identify and label: producers, consumers and decomposers. Compare power circuits and establish similarities between them. (at the beginning of each chain there is plant food, then there is a herbivore, and at the end there is a predatory animal). Name the way plants and animals feed. (plants are autotrophs, i.e. they produce organic matter themselves, animals – heterotrophs – consume finished organic matter).

Conclusion: a food chain is a series of organisms sequentially feeding on each other. Food chains begin with autotrophs - green plants.

Task No. 2. Compare two food chains, identify similarities and differences.

1. Clover - rabbit - wolf
2. Plant litter - earthworm - blackbird - hawk - sparrowhawk (The first food chain begins with producers - living plants, the second with plant residues - dead organic matter).

In nature, there are two main types of food chains: pasture (grazing chains), which begin with producers, detrital (decomposition chains), which begin with plant and animal residues, animal excrement.

Conclusion: Therefore, the first food chain is pasture, because begins with producers, the second is detrital, because starts with dead organic matter.

All components of food chains are distributed into trophic levels. A trophic level is a link in the food chain.

Task No. 3. Make a food chain, including the following organisms: caterpillar, cuckoo, tree with leaves, buzzard, soil bacteria. Indicate producers, consumers, decomposers. (tree with leaves - caterpillar - cuckoo - buzzard - soil bacteria). Determine how many trophic levels this food chain contains (this chain consists of five links, therefore there are five trophic levels). Determine which organisms are located at each trophic level. Draw a conclusion.

• The first trophic level is green plants (producers),
• Second trophic level – herbivores (consumers of the 1st order)
• Third trophic level – small predators (2nd order consumers)
• Fourth trophic level – large predators (3rd order consumers)
• Fifth trophic level - organisms that consume dead organic matter - soil bacteria, fungi (decomposers)

In nature, each organism uses not one food source, but several, but in biogeocenoses food chains intertwine and form food web. For any community, you can draw up a diagram of all the food relationships of organisms, and this diagram will have the form of a network (we consider an example of a food network in Fig. 62 in the biology textbook by A.A. Kamensky and others)

5. Implementation of acquired knowledge.

Practical work in groups.

Task No. 1. Solving environmental situations

1. In one of the Canadian reserves, all wolves were destroyed in order to increase the herd of deer. Was it possible to achieve the goal in this way? Explain your answer.

2. Hares live in a certain territory. Of these, there are 100 small hares weighing 2 kg, and 20 of their parents weighing 5 kg. The weight of 1 fox is 10 kg. Find the number of foxes in this forest. How many plants must grow in the forest for hares to grow up?

3. A reservoir with rich vegetation is home to 2000 water rats, each rat consumes 80g of plants per day. How many beavers can this pond feed if a beaver consumes an average of 200 g of plant food per day?

4. Present the disorganized facts logically correct sequence(in the form of numbers).

1. Nile perch began to eat a lot of herbivorous fish.

2. Having multiplied greatly, the plants began to rot, poisoning the water.

3. Smoking Nile perch required a lot of wood.

4. In 1960, British colonists released Nile perch into the waters of Lake Victoria, which quickly multiplied and grew, reaching a weight of 40 kg and a length of 1.5 m.

5. Forests on the shores of the lake were intensively cut down - so water erosion of the soil began.

6. Dead zones with poisoned water appeared in the lake.

7. The number of herbivorous fish decreased, and the lake began to be overgrown with aquatic plants.

8. Soil erosion has led to a decrease in the fertility of fields.

9. Poor soils did not produce crops, and the peasants went bankrupt .

6. Self-test of acquired knowledge in the form of a test.

1. Producers of organic substances in the ecosystem

A) producers

B) consumers

B) decomposers

D) predators

2. To which group do microorganisms living in the soil belong?

A) producers

B) consumers of the first order

B) consumers of the second order

D) decomposers

3. Name the animal that should be included in the food chain: grass -> ... -> wolf

B) hawk

4. Identify the correct food chain

A) hedgehog -> plant -> grasshopper -> frog

B) grasshopper -> plant -> hedgehog -> frog

B) plant -> grasshopper -> frog -> hedgehog

D) hedgehog -> frog -> grasshopper -> plant

5. In the ecosystem coniferous forest consumers of the 2nd order include

A) common spruce

B) forest mice

B) taiga ticks

D) soil bacteria

6. Plants produce organic substances from inorganic substances, therefore they play a role in food chains

A) final link

B) initial level

B) consumer organisms

D) destructive organisms

7. Bacteria and fungi play the role of:

A) producers of organic substances

B) consumers of organic substances

B) destroyers of organic substances

D) destroyers of inorganic substances

8. Identify the correct food chain

A) hawk -> tit -> insect larvae -> pine

B) pine -> tit -> insect larvae -> hawk

B) pine -> insect larvae -> tit -> hawk

D) insect larvae -> pine -> tit -> hawk

9. Determine which animal should be included in the food chain: cereals -> ? -> already -> kite

A) frog

D) lark

10. Identify the correct food chain

A) seagull -> perch -> fish fry -> algae

B) algae -> seagull -> perch -> fish fry

C) fish fry -> algae -> perch -> seagull

D) algae -> fish fry -> perch -> seagull

11. Continue the food chain: wheat -> mouse -> ...

B) gopher

B) fox

D) triton

7. General conclusions of the lesson.

Answer the questions:

1. How are organisms interconnected in biogeocenosis (food connections)
2. What is a food chain (a series of organisms sequentially feeding on each other)
3. What types of food chains are there (pastoral and detrital chains)
4. What is the name of the link in the food chain (trophic level)
5. What is a food web (intertwined food chains)

The transfer of energy by living organisms eating each other is called a food chain. These are specific relationships between plants, fungi, animals, and microorganisms that ensure the circulation of substances in nature. Also called a food chain.

Structure

All organisms feed, i.e. receive energy that powers life processes. The trophic chain system is formed by links. A link in the food chain is a group of living organisms connected to a neighboring group through the “food-consumer” relationship. Some organisms are food for other organisms, which in turn are also food for a third group of organisms.
There are three types of links:

• producers - autotrophs;
• consumers - heterotrophs;
• decomposers (destructors) - saprotrophs.

Rice. 1. Links in the food chain.

All three links form one chain. There can be several consumers (consumers of the first, second order, etc.). The basis of the chain can be producers or decomposers.

Producers include plants that transform organic substances with the help of light into organic substances, which, when eaten by plants, enter the body of the first-order consumer. The main characteristic of the consumer is heterotrophy. At the same time, consumers can consume both living organisms and dead ones (carrion).
Examples of consumers:

• herbivores - hare, cow, mouse;
• predators - leopard, owl, walrus;
• scavengers - vulture, Tasmanian devil, jackal.

Some consumers, including humans, occupy an intermediate position, being omnivores. Such animals can act as consumers of the first, second and even third order. For example, a bear eats berries and small rodents, i.e. is simultaneously a consumer of the first and second orders.

Reducers include:

• mushrooms;
• bacteria;
• protozoa;
• worms;
• insect larvae.

Rice. 2. Decomposers.

Decomposers feed on the remains of living organisms and their metabolic products, returning inorganic substances into the soil that producers consume.

Species

Food chains can be of two types:

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• pasture (grazing chain);
• detrital (decomposition chain).

Pasture chains are characteristic of meadows, fields, seas, and reservoirs. The beginning of the grazing chain is autotrophic organisms - photosynthetic plants.
Next, the chain links are arranged as follows:

• First-order consumers are herbivores;
• second-order consumers are predators;
• third-order consumers are larger predators;
• decomposers.

In marine and oceanic ecosystems, grazing chains are longer than on land. They may include up to five consumer orders. The basis of marine chains is photosynthetic phytoplankton.
The following links are formed by several consumers:

• zooplankton (crustaceans);
• small fish (sprats);
• large predatory fish (herring);
• large carnivorous mammals(seals);
• apex predators (killer whales);
• decomposers.

Detritus chains are characteristic of forests and savannas. The chain begins with decomposers that feed on organic remains (detritus) and are called detriophages. These include microorganisms, insects, and worms. All these living organisms become food for top predators, for example, birds, hedgehogs, and lizards.

Examples of two types of food chains:

• pasture : clover - hare - fox - microorganisms;
• detrital : detritus - fly larvae - frog - snake - hawk - microorganisms.

Rice. 3. Example of a food chain.

The top of the food chain is always occupied by a predator, which is a consumer last order in its area. The number of top predators is not regulated by other predators and depends only on external environmental factors. Examples are killer whales, monitor lizards, and large sharks.

What have we learned?

We found out what food chains there are in nature and how the links are located in them. All living organisms on Earth are interconnected food chains, through which energy is transmitted. Autotrophs produce themselves nutrients and are food for heterotrophs, which, when dying, become a breeding ground for saprotrophs. Decomposers can also become food for consumers and produce a nutrient medium for producers without interrupting the food chain.

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Cycle of substances in nature and food chains

All living organisms are active participants in the cycle of substances on the planet. Using oxygen, carbon dioxide, water, mineral salts and other substances, living organisms feed, breathe, excrete products, and reproduce. After death, their bodies decompose into simple substances and return to the external environment.

The transfer of chemical elements from living organisms to the environment and back does not stop for a second. Thus, plants (autotrophic organisms) take carbon dioxide, water and mineral salts from the external environment. In doing so, they create organic matter and release oxygen. Animals (heterotrophic organisms), on the contrary, inhale the oxygen released by plants, and by eating plants, they assimilate organic substances and release carbon dioxide and food debris. Fungi and bacteria eat the remains of living organisms and convert organic substances into minerals, which accumulate in soil and water. And minerals are again absorbed by plants. This is how nature maintains a constant and endless cycle of substances and maintains the continuity of life.

The cycle of substances and all the transformations associated with it require a constant flow of energy. The source of such energy is the Sun.

On earth, plants absorb carbon from the atmosphere through photosynthesis. Animals eat plants, passing carbon up the food chain, which we'll talk about later. When plants and animals die, they transfer carbon back to the earth.

At the surface of the ocean, carbon dioxide from the atmosphere dissolves into the water. Phytoplankton absorb it for photosynthesis. Animals that eat plankton exhale carbon into the atmosphere and thereby transmit it further along the food chain. After the death of phytoplankton, it can be processed into surface waters or settle to the bottom of the ocean. Over millions of years, this process has transformed the ocean floor into the planet's rich carbon reservoir. Cold currents transport carbon to the surface. When water is heated, it is released as a gas and enters the atmosphere, continuing the cycle.

Water constantly circulates between the seas, the atmosphere and the land. Under the rays of the sun it evaporates and rises into the air. There, droplets of water collect into clouds and clouds. They fall to the ground as rain, snow or hail, which turns back into water. Water is absorbed into the ground and returned to the seas, rivers and lakes. And everything starts all over again. This is how the water cycle occurs in nature.

Most of the water is evaporated by the oceans. The water in it is salty, and the water that evaporates from its surface is fresh. Thus, the ocean is the world’s “factory” of fresh water, without which life on Earth is impossible.

THREE STATES OF MATTER. There are three state of aggregation substances - solid, liquid and gaseous. They depend on temperature and pressure. IN everyday life we can observe water in all three of these states. Moisture evaporates and moves from liquid state into gaseous, that is, water vapor. It condenses and turns into liquid. At sub-zero temperatures Water freezes and turns into a solid state - ice.

Gyre complex substances in living nature includes food chains. This is a linear closed sequence in which each living creature feeds on someone or something and itself serves as food for another organism. Within the grassland food chain, organic matter is created by autotrophic organisms such as plants. Plants are eaten by animals, which in turn are eaten by other animals. Decomposer fungi decompose organic remains and serve as the beginning of the detrital trophic chain.

Each link in the food chain is called a trophic level (from the Greek word “trophos” - “nutrition”).
1. Producers, or producers, produce organic substances from inorganic ones. Producers include plants and some bacteria.
2. Consumers, or consumers, consume ready-made organic substances. First-order consumers feed on producers. 2nd order consumers feed on 1st order consumers. Consumers of the 3rd order feed on consumers of the 2nd order, etc.
3. Reducers, or destroyers, destroy, that is, mineralize organic substances to inorganic ones. Decomposers include bacteria and fungi.

DETRITAL FOOD CHAINS. There are two main types of food chains - grazing (grazing chains) and detrital (decomposition chains). The basis of the pasture food chain is made up of autotrophic organisms that are eaten by animals. And in detrital trophic chains, most of the plants are not consumed by herbivores, but die and then decompose by saprotrophic organisms (for example, earthworms) and are mineralized. Thus, detrital trophic chains start from detritus, and then go to detritivores and their consumers - predators. On land, these are the chains that predominate.

WHAT IS AN ECOLOGICAL PYRAMID? An ecological pyramid is a graphical representation of the relationships between different trophic levels of a food chain. The food chain cannot contain more than 5-6 links, because when moving to each next link, 90% of the energy is lost. The basic rule of the ecological pyramid is based on 10%. So, for example, to form 1 kg of mass, a dolphin needs to eat about 10 kg of fish, and they, in turn, need 100 kg of food - aquatic vertebrates, which need to eat 1000 kg of algae and bacteria to form such mass. If these quantities are depicted on an appropriate scale in the order of their dependence, then a kind of pyramid is actually formed.

FOOD NETWORKS. Often the interactions between living organisms in nature are more complex and visually resemble a network. Organisms, especially carnivores, can feed on a wide variety of creatures from different food chains. Thus, food chains intertwine to form food webs.

TROPHIC CHAINS

Purpose of work: obtaining skills in compiling and analyzing food (trophic) chains.

General information

There are various connections between living organisms in ecosystems. One of the central connections, which cements a variety of organisms into one ecosystem, is food, or trophic. Food connections unite organisms with each other according to the food-consumer principle. This leads to the emergence of food or trophic chains. Within an ecosystem, energy-containing substances are created by autotrophic organisms and serve as food for heterotrophs. Food connections are mechanisms for transferring energy from one organism to another. A typical example is an animal eating plants. This animal, in turn, can be eaten by another animal. Energy transfer can occur in this way through a number of organisms.

Each subsequent one feeds on the previous one, which supplies it with raw materials and energy.

This sequence of transfer of food energy in the process of nutrition from its source through a successive series of living organisms is called food (trophic) chain, or power circuit. Trophic chains- this is the path of unidirectional flow of solar energy absorbed during the process of photosynthesis through living organisms of the ecosystem into the environment, where the unused part of it is dissipated in the form of low-temperature thermal energy.

mice, sparrows, pigeons. Sometimes in ecological literature any food connection is called a “predator-prey” connection, meaning that a predator is an eater. The stability of the predator-prey system is ensured by the following factors:

- ineffectiveness of the predator, flight of the prey;

- environmental restrictions imposed by the external environment on population size;

- availability of alternative food resources for predators;

- reducing the delay in the predator's reaction.

The location of each link in the food chain is trophic level. The first trophic level is occupied by autotrophs, or so-called primary producers. Organisms of the second trophic level are called first-

primary consumers, the third - secondary consumers, etc.

Trophic chains are divided into two main types: grazing (grazing chains, consumption chains) and editrite (decomposition chains).

Plant → hare → wolf Producer → herbivore → carnivore

The following food chains are also widespread:

Plant material (eg nectar) → fly → spider → shrew → owl.

Juice rose bush→ aphid → ladybug→ spider → insectivorous bird → bird of prey.

In aquatic, particularly marine, ecosystems, predator food chains are longer than in terrestrial ones.

The detrital chain begins with dead organic matter - detritus, which is destroyed by detritivores eaten by small predators, and ends with the work of decomposers that mineralize organic remains. Deciduous forests play an important role in the detrital food chains of terrestrial ecosystems, most of the foliage of which is not consumed by herbivores and is part of the forest litter. The leaves are crushed by numerous detritivores (fungi, bacteria, insects), then ingested by earthworms, which uniformly distribute humus in the surface layer of soil, forming a mull. Decomposing

microorganisms completing the chain produce the final mineralization of dead organic residues (Fig. 1).

In general, typical detritus chains of our forests can be represented as follows:

leaf litter → earthworm → blackbird → sparrowhawk;

dead animal → carrion fly larvae → grass frog → snake.

Rice. 1. Detrital food chain (according to Nebel, 1993)

As a starting point organic material, which is subjected to biological processing in the soil by organisms inhabiting the soil; we can take wood as an example. Wood that falls on the soil surface is primarily processed by the larvae of longhorned beetles, borers, and borers, which use it for food. They are replaced by mushrooms, the mycelium of which primarily settles in the passages made in the wood by insects. Mushrooms further loosen and destroy the wood. Such loose wood and the mycelium itself turn out to be food for fireflower larvae. At the next stage, ants settle in the already severely damaged wood, destroying almost all the larvae and creating conditions for a new generation of fungi to settle in the wood. Snails begin to feed on such mushrooms. Decomposer microbes complete the destruction and humification of wood.

Similarly, there is humification and mineralization of manure from wild and domestic animals entering the soil.

As a rule, the food of every living creature is more or less varied. Only all green plants “feed” the same: carbon dioxide and ions of mineral salts. In animals, cases of narrow specialization of nutrition are quite rare. As a result of a possible change in animal nutrition, all ecosystem organisms are involved in a complex network of food relationships. Food chains are closely intertwined with each other forming food or trophic networks. In a food web, each species is directly or indirectly connected to many. An example of a trophic network with the placement of organisms by trophic levels is shown in Fig. 2.

Food webs in ecosystems are very complex, and we can conclude that the energy entering them takes a long time to migrate from one organism to another.

Rice. 2. Trophic network

In biocenoses, food connections play a dual role. Firstly, they

provide the transfer of matter and energy from one organism to another.

Thus, species coexist together and support each other’s life. Secondly, food connections serve as a mechanism for regulating numerical

Representation of trophic networks can be traditional (Fig. 2) or using directed graphs (digraphs).

A geometrically oriented graph can be represented as a set of vertices, denoted by circles with vertex numbers, and arcs connecting these vertices. An arc specifies the direction from one vertex to another. A path in a graph is a finite sequence of arcs in which the beginning of each subsequent arc coincides with the end of the previous one. An arc can be designated by the pair of vertices that it connects. A path is written as a sequence of vertices through which it passes. A path is called a path whose starting vertex coincides with the final vertex.

FOR EXAMPLE:

						Peaks;
		A – arcs;
		B – contour passing through vertices 2, 4,

B 3;

1, 2 or 1, 3, 2 – paths from the top

		to the top

In the power network, the top of the graph displays modeling objects; arcs, indicated by arrows, lead from the prey to the predator.

Any living organism occupies a certain ecological niche. An ecological niche is a set of territorial and functional characteristics of a habitat that meet the requirements of a given species. No two species have identical niches in ecological phase space. According to Gause's principle of competitive exclusion, two species with similar ecological requirements long time cannot occupy one ecological niche. These species compete, and one of them displaces the other. Based on power networks, you can build competition graph. Living organisms in the competition graph are displayed as vertices of the graph; an edge (a connection without direction) is drawn between the vertices if there is a living organism that serves as food for the organisms displayed by the above vertices.

The development of a competition graph allows one to identify competing species of organisms and analyze the functioning of the ecosystem and its vulnerability.

The principle of matching the growth in complexity of an ecosystem with increasing its stability is widely accepted. If the ecosystem is represented by a food network, you can use different ways Difficulty Dimensions:

- determine the number of arcs;

- find the ratio of the number of arcs to the number of vertices;

Trophic level is also used to measure the complexity and diversity of the food web, i.e. the place of the organism in the food chain. The trophic level can be determined both by the shortest and by the longest food chain from the vertex in question, which has a trophic level equal to “1”.

PROCEDURE FOR PERFORMANCE OF THE WORK

Task 1

Make a network for 5 participants: grass, birds, insects, hares, foxes.

Task 2

Establish the food chains and trophic level along the shortest and longest path of the food network from task “1”.

			Trophic level and food chain
power supply network		along the shortest path		along the longest path

4. Insects

Note: The grazing food chain begins with the producers. The organism listed in column 1 is the top trophic level. For consumers of the first order, the long and short paths of the trophic chain coincide.

Task 3

Propose a trophic network according to the task option (Table 1P) and make a table of trophic levels along the longest and shortest paths. The food preferences of consumers are shown in Table. 2P.

Task 4

Make a trophic network according to Fig. 3 and place its members according to trophic levels

REPORT PLAN

1. Purpose of the work.

2. Food web graph and competition graph based on the training example (tasks 1, 2).

3. Table of trophic levels based on the educational example (task 3).

4. Food network graph, competition graph, table of trophic levels according to the assignment option.

5. Scheme of the trophic network with the placement of organisms by trophic levels (according to Fig. 3).

Rice. 3. Tundra biocenosis.

First row: small passerines, various dipterous insects, rough-legged buzzard. Second row: arctic fox, lemmings, polar owl. Third row: white partridge, white hares. Fourth row: goose, wolf, reindeer.

Literature

1. Reimers N.F. Nature management: Dictionary-reference book. – M.: Mysl, 1990. 637 p.

2. Animal life in 7 volumes. M.: Education, 1983-1989.

3. Zlobin Yu.A. General ecology. Kyiv: Naukova Dumka, 1998. – 430 p.

4. Stepanovskikh A.S. Ecology: Textbook for universities. – M.: UNITIDAN,

5. Nebel B. Science of environment: how the world works. – M.: Mir, 1993.

–t.1 – 424 p.

6. Ecology: Textbook for technical universities / L.I. Tsvetkova, M.I. Alekseev, etc.; Ed. L.I. Tsvetkova.–M.: ASV; St. Petersburg: Khimizdat, 2001.-552 p.

7. Girusov E.V. and others. Ecology and economics of environmental management: Textbook for universities / Ed. Prof. E.V. Girusova. – M.: Law and Law, UNITY,

		Table 1P
		Species structure of biocenosis
	Name bio-	Species composition of the biocenosis
	Cedarwood	Korean cedar, yellow birch, variegated hazel,
		sedge, white hare, flying squirrel, common squirrel,
		wolf, brown bear, Himalayan bear, sable,
		mouse, nutcracker, woodpecker, fern.
	swampy	Sedges, iris, common reed. A wolf, a fox come in,
		brown bear, roe deer, mouse. Amphibians – Siberian salamander
	reed grass	sky, Far Eastern tree frog, Siberian frog. Ulit-
		ka, earthworm. Birds – Far Eastern White
		stork, piebald harrier, pheasant, red-crowned crane, white-naped beetle
		Ravl. Swallowtail butterflies.
	White birch	Aspen, flat-leaved birch (white) aspen, alder, dio-
		rather nipponica (herbaceous vine), grasses, sedges,
		forbs (clover, rank). Shrubs – Lespedeza, Rya-
		binnik, meadowsweet. Mushrooms – boletus, boletus.
		Animals - raccoon dog, wolf, fox, bear
		ry, weasel, wapiti, roe deer, Siberian salamander, frog-
		ka Siberian mouse. Birds – great spotted eagle, tit,
	Spruce grass-	Plants – fir, larch, Korean cedar, maple, rowan
		mountain ash, honeysuckle, spruce, sedges, cereals.
	shrubby	Animals – white hare, common squirrel, flying squirrel
		ha, wolf, brown bear, Himalayan bear, sable,
		kharza, lynx, wapiti, elk, hazel grouse, owl, mouse, butterfly
		Plants - Mongolian oak, aspen, birch,
		linden, elm, maakia (the only one in the Far East
		tree belonging to the legume family), shrubs –
		lespedeza, viburnum, mountain ash, wild rose,
		herbs – lily of the valley, sedge, hellebore, wild garlic, bells,
		bells. Animals – chipmunk, raccoon dog
		ka, wolf, fox, brown bear, badger, weasel, lynx, ka-
		ban, wapiti, roe deer, hare, Siberian salamander, tree frog
		Far Eastern, Siberian frog, mouse, lizard
		hawk, jay, woodpecker, nuthatch, woodcutter beetle, blacksmith
		Plants - aspen, birch, hawthorn, shi-
		povnik, spirea, peony, cereals. Animals – raccoon
		dog, wolf, fox, brown bear, weasel, wapiti, co-
		sulya, Siberian salamander, Siberian frog, mouse, lizard
		ritsa viviparous, jay, woodpecker, nuthatch, spotted eagle,
		woodcutter beetle, grasshopper,

			Table 2P
		Nutritional spectrum of some species
Living organisms			Food cravings - “menu”
		Grass (cereals, sedges); aspen, linden, hazel bark; berries (strawberries)
		Cereal seeds, insects, worms.
flying squirrel
		and their larvae.
Plants		Consume solar energy and minerals, water,
		oxygen, carbon dioxide.
		Rodents, hares, frogs, lizards, small birds.
Common squirrel		Pine nuts, hazelnuts, acorns, cereal seeds.
		Shrub seeds (Eleutherococcus), berries (lingonberries), insects
		and their larvae.
Insect larvae		Mosquito larvae – algae, bacteria.
wet mosquitoes,		Dragonfly larvae are insects and fish fry.
		Herbal juice.
		Rodents, hares, frogs, lizards.
Steller's sea eagle		Fish, small birds.
Brown bear		Euryphage, prefers animal food: wild boars (pork)
		ki), fish (salmon). Berries (raspberries, bird cherry, honeysuckle, pigeons)
		ka), roots.
Himalayan bear		Angelica (bear's pipe), wild berries(lingonberries, raspberries, cherry
		fly, blueberry), honey (wasps, bees), lilies (bulbs), mushrooms,
		nuts, acorns, ant larvae.
Insects		Herbaceous plants, tree leaves.
		Mouse, squirrel, hares, hazel grouse.
		Predator. Hares, squirrels, pigs.
			grass (wintering horsetail), legumes (vetch, china),
			hazel bark, willow bark, birch undergrowth, roots of shrubs (forest
		shina, raspberries).
		Buds of birch, alder, linden; cereals; rowan berries, viburnum; needles fir-
		you, spruce, larches.
		Mouse, chipmunk, hares, fox cubs, snakes (snake), lizard, white
		ka, bat.
		Mice, hares, roe deer, in a flock can kill deer, elk, and wild boar.
Earwig		Predator. Fleas, beetles (small), slugs, earthworms.
Woodcutter beetle		Bark of birch, cedar, linden, maple, larch.
		Plant pollen.
peacock eye
		Mouse, hares, chipmunk, Siberian salamander, crane chicks,
		stork, ducks; Far Eastern tree frog, baby pheasants, worms,
		large insects.
		Bark of hazel, birch, willow, oak, sedge, reed grass, reed; leaves are white
		cuts, willow, oak, hazel.
		Predator. Crustaceans, mosquito larvae.

Tree frog far-		Aquatic invertebrates.
		Grasses (reed grass), sedge, mushrooms, plant residues and soil.
		Plants, fish and their eggs during spawning, insects and their larvae
earthworm		Dead plant debris.
Far Eastern		Snail, tree frog, Siberian frog, fish (loach, sleeper), snakes,
white stork		mice, locusts, passerine chicks.
Japanese crane		Sedge rhizomes, fish, frogs, small rodents, chicks.
Pied harrier		Mouse, small birds (buntings, warblers, sparrows), frogs,
		lizards, large insects.
		Birch, alder, reed buds.
Swallowtail butterflies		Pollen from plants (violets, corydalis).
		Carnivorous, prefers animal food - hares, young
		moose calves, roe deer, deer, wild boars.
Raccoon co-		Rotten fish, birds (larks, fescue birds, warblers).
		Branch food (birch, aspen, willow, hazel; oak, linden leaves),
		acorns, oak bark, algae in shallow waters, three-leaf watch.
		Mosquito, spiders, ants, grasshoppers.
Lizard alive		Insects and their larvae, earthworms.
spotted eagle		Predator. Small mammals, pheasant, mice, hares, foxes,
		birds, fish, rodents.
		Squirrels, chipmunks, birds.
Chipmunk		Seeds of apple tree, rose hip, viburnum, field ash, mountain ash; mushrooms;
		nuts; acorns.
		Roots, earthworms, mice, insects (ants and their larvae).
		Predator. Mice.
		Cereal seeds, nuts.
		Pine nuts, acorns, berries (rowan), apple tree.
		Lumberjack beetles, wood-boring insects.
		Wild boar, hare, roe deer, elk calves, fawns, elk, deer (wounded animals).
Nuthatch		Insects; tree seeds, berries, nuts.
Lemmings		Granivores. Sedges, shiksha, cereals.
		Granivores.
		Predator. Lemmings, chicks of partridges, seagulls.
polar owl		Lemmings, mice, voles, hares, ducks, pheasants, black grouse.
Ptarmigan		Herbivores. Cereal seeds; buds of birch, willow, alder.
		Herbivores, leaves and bark of trees, moss - moss.
White hare		In winter - bark; in summer - berries, mushrooms.
		Herbivores. Sedges, grasses, algae, shoots of aquatic plants.
Reindeer		Resin moss, cereals, berries (cloudberries, cranberries), mice.
		Roe deer, wapiti, sika deer, wild boar.
Daphnia, Cyclops		Unicellular algae.