Ecological chain in nature. Examples of food chains in different forests

There are complex nutritional interactions between autotrophs and heterotrophs in ecosystems. Some organisms eat others, and thus carry out the transfer of substances and energy - the basis of the functioning of the ecosystem.

Within an ecosystem, organic matter is created by autotrophic organisms, such as plants. Plants are eaten by animals, which in turn are eaten by other animals. Such a sequence is called a food chain (Fig. 1), and each link in the food chain is called a trophic level.

Distinguish

pasture food chains(eating chains) - food chains that begin with autotrophic photosynthetic or chemosynthetic organisms (Fig. 2.). Pasture food chains are predominantly found in terrestrial and marine ecosystems.

An example is the grassland food chain. Such a chain begins with the capture of solar energy by a plant. A butterfly feeding on the nectar of a flower is the second link in this chain. Dragonfly - a predatory flying insect - attacks a butterfly. A frog hiding among the green grass catches a dragonfly, but itself serves as prey for such a predator as snake. He could have digested a frog all day, but before the sun had set, he himself became the prey of another predator.

The food chain, going from the plant through the butterfly, dragonfly, frog, grass snake to the hawk, indicates the direction of the movement of organic substances, as well as the energy contained in them.

In the oceans and seas, autotrophic organisms (unicellular algae) exist only up to the depth of light penetration (up to a maximum of 150-200 m). Heterotrophic organisms living in deeper layers of water rise to the surface at night to feed on algae, and in the morning again go to the depth, making daily vertical migrations up to 500-1000 m long. In turn, with the onset of morning, heterotrophic organisms from even deeper layers rise to the top to feed on the descending from the surface layers of other organisms.

Thus, in the deep seas and oceans there is a kind of "food ladder", thanks to which the organic matter created by autotrophic organisms in the surface layers of water is transferred along the chain of living organisms to the very bottom. In this regard, some marine ecologists consider the entire water column to be a single biogeocenosis. Others believe that the environmental conditions in the surface and bottom layers of water are so different that they cannot be considered as a single biogeocenosis.

Detrital food webs(decomposition chains) - food chains that begin with detritus - dead plant remains, corpses and animal excrement (Fig. 2).

Detrital chains are most typical for communities of continental water bodies, the bottom of deep lakes, and oceans, where many organisms feed on detritus formed by dead organisms from the upper illuminated layers of a water body or that have entered the water body from terrestrial ecosystems, for example, in the form of leaf litter.

The ecosystems of the bottom of the seas and oceans, where sunlight does not penetrate, exist only due to the constant settling of dead organisms that live in the surface layers of water. The total mass of this substance in the World Ocean per year reaches at least several hundred million tons.

Detrital chains are also widespread in forests, where most of the annual increase in the live weight of plants is not consumed directly by herbivorous animals, but dies off, forming litter, and then decomposes by saprotrophic organisms, followed by mineralization by decomposers. Of great importance in the decomposition of dead residues plant origin, especially wood, have mushrooms.

Heterotrophic organisms that feed directly on detritus are called detritophages. In terrestrial ecosystems, they are many species of insects, worms, etc. Large detritus feeders, which include some species of birds (vultures, crows, etc.) and mammals (hyenas, etc.), are called scavengers.

In aquatic ecosystems, the most common detritophages are arthropods - aquatic insects and their larvae, and crustaceans. Detritophages can feed on other, larger heterotrophic organisms, which themselves can serve as food for predators.

Trophic levels

Typically, different trophic levels in ecosystems are not spatially separated. However, in some cases they are quite clearly differentiated. For example, in geothermal springs, autotrophic organisms - blue-green algae and autotrophic bacteria that form specific algal-bacterial communities ("mats") are common at temperatures above 40-45 ° C. At lower temperatures, they do not survive.

On the other hand, heterotrophic organisms (molluscs, larvae of aquatic insects, etc.) do not occur in geothermal springs at temperatures above 33–36°C, so they feed on mat fragments carried by the current to zones with lower temperatures.

Thus, in such geothermal springs, an autotrophic zone is clearly distinguished, where only autotrophic organisms are distributed, and a heterotrophic zone, where autotrophic organisms are absent and only heterotrophic organisms are found.

food webs

In ecological systems, despite the existence of a number of parallel food chains, for example,

herbaceous vegetation -> rodents -> small carnivores
herbaceous vegetation -> ungulates -> large carnivores,

which unite the inhabitants of the soil, herbaceous cover, tree layer, there are other relationships. In most cases, the same organism can serve as a food source for many organisms and thus be integral part different food chains and prey to different predators. For example, daphnia can be eaten not only by small fish, but also by the predatory crustacean cyclops, and roach can be eaten not only by pike, but also by otters.

The trophic structure of the community reflects the ratio between producers, consumers (separately of the first, second, etc. orders) and decomposers, expressed either by the number of individuals of living organisms, or by their biomass, or by the energy contained in them, calculated per unit area per unit time.

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.

Rice. 1. Food chains in the terrestrial ecosystem

The set of organisms united by one type of food and occupying a certain position in the food chain is called trophic level. Organisms that receive their energy from the Sun through the same number of steps belong to the same trophic level.

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

Nature is complex. All its elements, 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.

Breaking food chains can have a particularly negative impact on forests, whether they are forest biocenoses of the temperate zone or biocenoses of the tropical forest that are rich in species diversity. Many species of trees, shrubs or herbaceous plants use the services of a particular pollinator - bees, wasps, butterflies or hummingbirds that live within the range of this plant species. As soon as the last flowering tree or herbaceous plant dies, the pollinator will be forced to leave this habitat. As a result, phytophages (herbivores) that feed on these plants or fruits of the tree will die. Predators that hunt phytophages will be left without food, and then changes will sequentially affect the rest of the food chain. As a result, they will also affect a person, since he has his own specific place in the food chain.

Food chains can be divided into two main types: grazing and detrital. Food prices that begin with autotrophic photosynthetic organisms are called pasture, or eating 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. Its protective coloration allows it to lie in wait for the victim, but does not save it from another predator - the common 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 detritus, or decomposition chain. 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 the 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 forest biocenoses, the detrital chain begins with the decomposition of dead organic matter by saprophage animals. Soil invertebrates (arthropods, worms) and microorganisms take the most active part in the decomposition of organic matter. There are also large saprophages - insects that prepare the substrate for organisms that carry out mineralization processes (for bacteria and fungi).

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.

General rule concerning any the food chain, states: at each trophic level of the community, most of the energy absorbed with food is spent on maintaining 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 each subsequent link in the food chain, the total amount of usable energy transferred to the next higher trophic level decreases.

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

Structure

All organisms feed, i.e. receive energy that provides life processes. The system of the trophic chain is formed by links. A link in the food chain is a group of living organisms connected with the neighboring group by the relationship "food - consumer". 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 of the food chain.

One chain includes all three links. 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 convert organic substances with the help of light into organic substances that, when eaten by plants, enter the body of a first-order consumer. The main feature 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;
predatory - 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 feeds on berries and small rodents; at the same time it is a consumer of the first and second orders.

Reducers include:

mushrooms;
bacteria;
protozoa;
worms;
insect larvae.

Rice. 2. Reducers.

Decomposers feed on the remains of living organisms and their metabolic products, returning to the soil inorganic substances that are consumed by producers.

Kinds

Food chains can be of two types:

What have we learned?

We found out what food chains are in nature and how the links are located in them. All living organisms on Earth are interconnected by food chains through which energy is transferred. Autotrophs themselves produce 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.

Topic quiz

Report Evaluation

Average rating: 4.7. Total ratings received: 203.

The transfer of energy in an ecosystem is carried out through the so-called food chains. In turn, the food chain is the transfer of energy from its original source (usually autotrophs) through a number of organisms, by eating some by others. Food chains are divided into two types:

Scotch pine => Aphids => Ladybugs => Spiders => Insectivores

birds => birds of prey.

Grass => Herbivorous mammals => Fleas => Flagellates.

2) Detrital food chain. It originates from dead organic matter (the so-called. detritus), which is either consumed by small, mostly invertebrate animals, or decomposed by bacteria or fungi. Organisms that consume dead organic matter are called detritivores, decomposing it - destructors.

Grassland and detrital food webs usually co-exist in ecosystems, but one type of food web almost always dominates the other. In some specific environments (for example, underground), where, due to the lack of light, the vital activity of green plants is impossible, only detrital food chains exist.

In ecosystems, food chains are not isolated from each other, but are closely intertwined. They constitute the so-called food webs. This is because each producer has not one, but several consumers, which, in turn, can have several food sources. The relationships within the food web are clearly illustrated in the diagram below.

Food web diagram.

In food chains, so-called trophic levels. Trophic levels classify organisms in the food chain according to their type of activity or source of energy. Plants occupy the first trophic level (the level of producers), herbivores (consumers of the first order) belong to the second trophic level, predators that eat herbivores form the third trophic level, secondary predators - the fourth, etc. first order.

Energy flow in an ecosystem

As we know, the transfer of energy in an ecosystem is carried out through food chains. But not all the energy of the previous trophic level goes to the next one. As an example, the following situation can be given: the net primary production in an ecosystem (that is, the amount of energy accumulated by producers) is 200 kcal/m^2, secondary productivity (the energy accumulated by first-order consumers) is 20 kcal/m^2 or 10% from the previous trophic level, the energy of the next level is 2 kcal / m ^ 2, which is equal to 20% of the energy of the previous level. As can be seen from this example, with each transition to a higher level, 80-90% of the energy of the previous link in the food chain is lost. Such losses are due to the fact that a significant part of the energy during the transition from one stage to another is not absorbed by representatives of the next trophic level or is converted into heat that is not available for use by living organisms.

Universal model of energy flow.

Energy input and output can be considered using universal energy flow model. It applies to any living component of an ecosystem: plant, animal, microorganism, population, or trophic group. Such graphical models, interconnected, can reflect food chains (when the energy flow diagrams of several trophic levels are connected in series, an energy flow diagram in the food chain is formed) or bioenergetics in general. The energy supplied to the biomass on the diagram is denoted I. However, part of the incoming energy does not undergo transformation (indicated in the figure as N.U.). For example, this happens when part of the light passing through plants is not absorbed by them, or when part of the food passing through the digestive tract of an animal is not absorbed by its body. learned (or assimilated) energy (indicated by A) is used for various purposes. It is spent on breathing (in the diagram- R) i.e. to maintain the vital activity of biomass and to produce organic matter ( P). Products, in turn, take various forms. It is expressed in energy costs for the growth of biomass ( G), in various releases of organic matter into the environment ( E), in the energy reserve of the body ( S) (an example of such a reserve is fat accumulation). The stored energy forms the so-called working loop, since this part of the production is used to provide energy in the future (for example, a predator uses its energy supply to search for new prey). The remainder of the production is biomass ( B).

The universal model of energy flow can be interpreted in two ways. First, it may represent a population of a species. In this case, the energy flow channels and connections of the species under consideration with other species represent a diagram of the food chain. Another interpretation treats the energy flow model as an image of some energy level. Then the biomass rectangle and energy flow channels represent all populations supported by the same energy source.

In order to visually show the difference in approaches to interpreting the universal model of energy flow, we can consider an example with a population of foxes. Part of the diet of foxes is vegetation (fruits, etc.), while the other part is herbivores. To emphasize the aspect of intrapopulation energy (the first interpretation of the energy model), the entire population of foxes should be depicted as a single rectangle, if metabolism is to be distributed ( metabolism- metabolism, metabolic rate) of the fox population into two trophic levels, that is, to display the ratio of the roles of plant and animal food in metabolism, it is necessary to build two or more rectangles.

Knowing the universal model of energy flow, it is possible to determine the ratio of the values of the energy flow at different points in the food chain. Expressed as a percentage, these ratios are called environmental efficiency. There are several groups of ecological efficiency. The first group of energy relations: B/R and P/R. The proportion of energy expended on respiration is large in populations of large organisms. When stressed by the external environment R increases. Value P significant in active populations of small organisms (for example, algae), as well as in systems that receive energy from outside.

The next group of relationships: A/I and P/A. The first of these is called efficiency of assimilation(i.e., the efficiency of using the energy received), the second - tissue growth efficiency. Assimilation efficiency can vary from 10 to 50% or more. It can either reach a small value (during the assimilation of light energy by plants), or have large values (during the assimilation of food energy by animals). Usually the efficiency of assimilation in animals depends on their food. In herbivorous animals, it reaches 80% when eating seeds, 60% when eating young leaves, 30-40% - older leaves, 10-20% when eating wood. In predatory animals, the efficiency of assimilation is 60-90%, since animal food is much easier to digest by the body than plant food.

The efficiency of tissue growth also varies widely. It reaches its highest values in those cases when the organisms are small and the conditions of their habitat do not require large energy expenditures to maintain the temperature that is optimal for the growth of organisms.

The third group of energy relations: P/B. If we consider P as the rate of production growth, P/B is the ratio of production at a particular point in time to biomass. If production is calculated for a certain period of time, the value of the ratio P/B is determined based on the average biomass over this period of time. In this case P/B is a dimensionless quantity and shows how many times the production is more or less than biomass.

It should be noted that the size of the organisms inhabiting the ecosystem affects the energy characteristics of the ecosystem. A relationship has been established between the size of an organism and its specific metabolism (metabolism per 1 g of biomass). The smaller the organism, the higher its specific metabolism and, consequently, the lower the biomass that can be maintained at a given trophic level of the ecosystem. For the same amount of energy used, larger organisms accumulate more biomass than smaller ones. For example, with an equal value of consumed energy, the biomass accumulated by bacteria will be much lower than the biomass accumulated by large organisms (for example, mammals). A different picture emerges when looking at productivity. Since productivity is the rate of biomass growth, it is greater in small animals, which have higher rates of reproduction and biomass renewal.

Due to the loss of energy within food chains and the dependence of metabolism on the size of individuals, each biological community acquires a certain trophic structure that can serve as a characteristic of an ecosystem. The trophic structure is characterized either by the standing crop or by the amount of energy fixed per unit area per unit time by each successive trophic level. The trophic structure can be depicted graphically in the form of pyramids, the basis of which is the first trophic level (the level of producers), and subsequent trophic levels form the "floors" of the pyramid. There are three types of ecological pyramids.

1) Pyramid of abundance (indicated by the number 1 in the diagram) It displays the number of individual organisms at each of the trophic levels. The number of individuals at different trophic levels depends on two main factors. The first of them is a higher level of specific metabolism in small animals compared to large ones, which allows them to have a numerical superiority over large species and higher reproduction rates. Another of the above factors is the existence of upper and lower limits on the size of their prey in predatory animals. If the prey is much larger than the predator in size, then he will not be able to overcome it. Prey of a small size will not be able to satisfy the energy needs of a predator. Therefore, for each predatory species there is an optimal size of victims. However, there are exceptions to this rule (for example, snakes kill animals that are larger than them with the help of poison). Pyramids of numbers can be turned "pointed" down if the producers are much larger than the primary consumers (for example, a forest ecosystem, where the producers are trees, and the primary consumers are insects).

2) Pyramid of biomass (in the diagram - 2). It can be used to visually show the ratio of biomass at each of the trophic levels. It can be direct, if the size and life span of the producers reach relatively large values (terrestrial and shallow water ecosystems), and reversed, when the producers are small in size and have a short life cycle (open and deep water bodies).

3) Pyramid of energy (in the diagram - 3). Reflects the amount of energy flow and productivity at each of the trophic levels. Unlike the pyramids of abundance and biomass, the pyramid of energy cannot be reversed, since the transition of food energy to higher trophic levels occurs with large energy losses. Consequently, the total energy of each previous trophic level cannot be higher than the energy of the next one. The above reasoning is based on the use of the second law of thermodynamics, so the pyramid of energy in an ecosystem serves as a clear illustration of it.

Of all the above-mentioned trophic characteristics of an ecosystem, only the pyramid of energy provides the most complete picture of the organization of biological communities. In the population pyramid, the role of small organisms is greatly exaggerated, and in the biomass pyramid, the importance of large ones is overestimated. In this case, these criteria are unsuitable for comparing the functional role of populations that differ greatly in the value of the ratio of metabolic intensity to the size of individuals. For this reason, it is the energy flow that serves as the most suitable criterion for comparing individual components of an ecosystem with each other, as well as for comparing two ecosystems with each other.

Knowledge of the basic laws of energy transformation in an ecosystem contributes to a better understanding of the processes of ecosystem functioning. This is especially important due to the fact that human intervention in its natural "work" can lead the ecological system to death. In this regard, he must be able to predict the results of his activities in advance, and the idea of energy flows in the ecosystem can provide greater accuracy of these predictions.

The cycle of substances in nature and the food chain

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

The transfer of chemical elements from living organisms to the environment and back does not stop even for a second. So, 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 eating plants, assimilate organic substances and release carbon dioxide and food residues. Fungi and bacteria use the remains of living organisms as food and turn organic substances into minerals that accumulate in soil and water. And minerals are again absorbed by plants. So in nature, a constant and endless cycle of substances is carried out and the continuity of life is maintained.

The cycle of matter and all the transformations associated with it require a constant supply of energy. The source of this 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 in a moment. 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 thus pass it along the food chain. After the death of phytoplankton, it can be processed in surface waters or settle to the bottom of the ocean. Over millions of years, this process has turned the ocean floor into a rich reservoir of carbon on the planet. Cold currents carry carbon to the surface. When water is heated, it is released as a gas and enters the atmosphere, continuing the cycle.

Water constantly makes a cycle between the seas, atmosphere and land. Under the rays of the sun, it evaporates and rises into the air. There, water droplets gather into clouds and clouds. They fall to the ground as rain, snow or hail, which turn back into water. Water soaks into the ground, returns to the seas, rivers and lakes. And everything starts over. This is how the water cycle works in nature.

Most of the water evaporates from the oceans. The water in it is salty, and the one that evaporates from its surface is fresh. Thus, the ocean is the global "factory" of fresh water, without which life on Earth is impossible.

THREE STATES OF MATTER. There are three aggregate states of matter - 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 passes from a liquid state to a gaseous state, that is, water vapor. It condenses and turns into a liquid. At sub-zero temperatures, water freezes and turns into a solid state - ice.

The cycle of complex substances in wildlife includes food chains. This is a linear closed sequence in which each living being feeds on someone or something and itself serves as food for another organism. Within the pasture 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 manufacturers, produce organic substances from inorganic ones. Producers include plants and some bacteria.
2. Consumers, or consumers, consume ready-made organic substances. Consumers of the 1st order feed on producers. Consumers of the 2nd order feed on consumers of the 1st order. 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.

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

WHAT IS AN ENVIRONMENTAL PYRAMID? An ecological pyramid is a graphic representation of the ratio of different trophic levels in 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 a mass. If, on an appropriate scale, these quantities are depicted in the order of their dependence, then a kind of pyramid is indeed formed.

FOOD NETS. Often the interaction between living organisms in nature is more complex, and visually it looks like a network. Organisms, especially predators, can feed on a variety of creatures, and from different food chains. Thus, food chains intertwine to form food webs.

Portal for the student. Self-training