Introduction
A striking example of a power chain:
Classification of living organisms regarding their role in the cycle of substances
Any food chain involves 3 groups of living organisms:
Producers (manufacturers) | Consumers (consumers) | Decomposers (destroyers) |
Autotrophic living organisms that synthesize organic matter from mineral matter using energy (plants). | Heterotrophic living organisms that consume (eat, process, etc.) living organic matter and transfer the energy contained in it through food chains. | Heterotrophic living organisms that destroy (process) dead organic matter of any origin into mineral matter. |
Connections between organisms in the food chain
The food chain, whatever it may be, creates close connections between various objects of both animate and inanimate nature. And the rupture of absolutely any link can lead to disastrous results and an imbalance in nature. The most important and integral component of any power chain is solar energy. Without it, there will be no life. When moving along the food chain, this energy is processed, and each organism makes it its own, passing only 10% to the next link.
When dying, the body enters other similar food chains, and thus the cycle of substances continues. All organisms can easily leave one food chain and move into another.
The role of natural areas in the cycle of substances
Naturally, organisms living in the same natural zone create their own special food chains with each other, which cannot be repeated in any other zone. Thus, the food chain of the steppe zone, for example, consists of a wide variety of grasses and animals. The food chain in the steppe practically does not include trees, since there are either very few of them or they are stunted. As for the animal world, artiodactyls, rodents, falcons (hawks and other similar birds) and various kinds of insects predominate here.
Classification of power circuits
The principle of ecological pyramids
If we consider specifically the chains starting with plants, then the entire cycle of substances in them comes from photosynthesis, during which solar energy is absorbed. Plants spend most of this energy on their vital functions, and only 10% goes to the next link. As a result, each subsequent living organism requires more and more creatures (objects) of the previous link. This is well demonstrated by ecological pyramids, which are most often used for these purposes. They are pyramids of mass, quantity and energy.
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 starts 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. The energy of the sun's ray falling on the tops of trees or on the surface of a pond is captured by green plants - be it 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 there are rarely more than 5-6 participants in a food chain. 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—that live in the euphotic zone and use solar energy to synthesize organic substances from inorganic chemical nutrients and carbon dioxide 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 a big fish. Its food consists of small fish that consume zooplankton, which lives off 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 of the 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 supply for higher animals without any prospects for progressive evolution.
In any geological epoch, organisms that were at the highest level in food relationships evolved at the highest speed, for example, in the Devonian, lobe-formed fish were 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 rise to a large number of 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 manure. 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.
A connection between two links is established if one group of organisms acts as food for another group. The first link of 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 - macroectopus - 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, aquatic plants, etc. as food. Short trophic chains are less stable and subject to greater fluctuations than long ones and complex 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 - the producing 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 reduce 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 cycle of 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 the food chain. 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.
BIBLIOGRAPHY
Akimova T.A., Khaskin V.V. Ecology. Tutorial. – M.: DONITI, 2005.
Moiseev A.N. Ecology in the modern world // Energy. 2003. No. 4.
Complex nutritional interactions exist between autotrophs and heterotrophs in ecosystems. Some organisms eat others, and thus carry out the transfer of substances and energy - the basis for 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. This sequence is called a food chain (Fig. 1), and each link in the food chain is called a trophic level.
Distinguish
Grassland food chains(grazing chains) - food chains that begin with autotrophic photosynthetic or chemosynthetic organisms (Fig. 2.). Pasture food chains are found predominantly in terrestrial and marine ecosystems.
An example is the grassland food chain. This chain begins with the capture of solar energy by the plant. The butterfly, feeding on the nectar of a flower, represents the second link in this chain. A 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 the grass snake. He could have spent the whole day digesting the frog, but before the sun had even set, he himself became the prey of another predator.
The food chain, going from a plant through a butterfly, dragonfly, frog, snake to a hawk, indicates the direction of movement of organic substances, as well as the energy contained in them.
In oceans and seas, autotrophic organisms (unicellular algae) exist only up to the depth of light penetration (maximum up to 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 they go deeper again, 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 other organisms descending from the surface layers.
Thus, in the deep seas and oceans there is a kind of “food ladder”, thanks to which organic matter created by autotrophic organisms in the surface layers of water is transported 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 environmental conditions in the surface and bottom layers of water are so different that they cannot be considered as a single biogeocenosis.
Detrital food chains(decomposition chains) - food chains that begin with detritus - dead remains of plants, corpses and animal excrement (Fig. 2).
Detrital chains are most typical for communities of continental reservoirs, the bottom of deep lakes, oceans, where many organisms feed on detritus formed by dead organisms of the upper illuminated layers of the reservoir or that entered the reservoir 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 there of dead organisms living 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 common in forests, where most of the annual increase in the live weight of plants is not consumed directly by herbivores, but dies, forming litter, and is then decomposed by saprotrophic organisms, followed by mineralization by decomposers. Fungi are of great importance in the decomposition of dead plant matter, especially wood.
Heterotrophic organisms that feed directly on detritus are called detritivores. In terrestrial ecosystems they are many species of insects, worms, etc. Large detritivores, which include some species of birds (vultures, crows, etc.) and mammals (hyenas, etc.) are called scavengers.
In aquatic ecosystems, the most common detritivores are arthropods - aquatic insects and their larvae, and crustaceans. Detritivores 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 separated in space. However, in some cases they are quite clearly differentiated. For example, in geothermal sources, autotrophic organisms - blue-green algae and autotrophic bacteria, forming 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 (mollusks, larvae of aquatic insects, etc.) are not found in geothermal springs at temperatures above 33-36 ° C, so they feed on fragments of mats carried by the current to areas with lower temperatures.
Thus, in such geothermal sources, an autotrophic zone is clearly distinguished, where only autotrophic organisms are common, and a heterotrophic zone, where autotrophic organisms are absent and only heterotrophic organisms are found.
Trophic networks
In ecological systems, although there are a number of parallel food chains, e.g.
herbaceous vegetation -> rodents -> small predators
herbaceous vegetation -> ungulates -> large predators,
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 part of 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 otter.
The trophic structure of a community reflects the relationship between producers, consumers (separately of the first, second, etc. orders) and decomposers, expressed either by the number of individuals of living organisms, or their biomass, or the energy contained in them, calculated per unit area per unit time.
In ecosystems, producers, consumers and decomposers are united by complex processes of transfer of substances and energy, which is contained in food created mainly by plants.
The transfer of potential food energy 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 use 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 through the process of photosynthesis.
In this case, 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 during nutrition.
Second trophic level form consumers of the 1st order - these are herbivorous organisms (phytophages) that feed on producers.
First-order consumers spend most of the energy contained in food to support their life processes, and the rest of the energy is used to build their own body, thereby transforming plant tissue into animal tissue.
Thus , 1st order consumers 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 2nd order consumers.
Third trophic level form consumers of the 2nd order - these are carnivorous organisms (zoophages) that feed exclusively on herbivorous organisms (phytophages).
Second-order consumers carry out the second stage of transformation of organic matter in food chains.
However, the chemical substances from which the tissues of animal organisms are built 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 during the transition 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 third-order consumers.
Fourth trophic level form consumers of the 3rd order - these are carnivores that feed only on carnivorous organisms.
Last level of the food chain occupied by decomposers (destructors and detritivores).
Reducers-destructors (bacteria, fungi, protozoa) in the process of their life activity decompose organic remains of all trophic levels of producers and consumers into mineral substances, which are returned to the producers.
All links of the food chain are interconnected and interdependent.
Between them, from the first to the last link, the transfer of substances and energy takes place. However, it should be noted that when energy is transferred from one trophic level to another, it is lost. As a result, the power chain cannot be long and most often consists of 4-6 links.
However, such food chains in their pure form are usually not found in nature, since each organism has several food sources, i.e. uses several types of food, and is itself used as a food product by numerous other organisms from the same food chain or even from different food chains.
For example:
Omnivorous organisms consume both producers and consumers as food, i.e. are simultaneously consumers of the first, second, and sometimes third order;
a mosquito that feeds on the blood of humans and predatory animals is at a very high trophic level. But the swamp sundew plant feeds on mosquitoes, which is thus 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 connections acts as an important mechanism for maintaining the integrity and functional stability of ecosystems.
In Fig.5. shows a simplified diagram of a power network for a terrestrial ecosystem.
Human intervention in natural communities of organisms through the intentional or unintentional elimination of a species often has unpredictable negative consequences and leads to disruption of the stability of ecosystems.
Fig.5. Scheme of the trophic network.
There are two main types of trophic chains:
pasture chains (grazing chains or consumption chains);
detrital chains (decomposition chains).
Pasture chains (grazing chains or consumption chains) are processes of synthesis and transformation of organic substances in trophic chains.
Pasture chains begin with producers. Living plants are eaten by phytophages (consumers of the first order), and the phytophages themselves are food for carnivores (consumers of the second order), which can be eaten by consumers of the third order, etc.
Examples of grazing chains for terrestrial ecosystems:
3 links: aspen → hare → fox; plant → sheep → human.
4 links: plants → grasshoppers → lizards → hawk;
nectar of plant flower → 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 step-by-step destruction and mineralization of organic substances in trophic chains.
Detrital chains begin with the gradual destruction of dead organic matter by detritivores, which successively replace each other in accordance with a specific type of nutrition.
At the last stages of destruction processes, reducers-destructors function, mineralizing the remains of organic compounds into simple inorganic substances, which are again used by producers.
For example, when dead wood decomposes, they successively replace each other: beetles → woodpeckers → ants and termites → destructive fungi.
Detrital chains are most common in forests, where most (about 90%) of the annual increase in plant biomass is not consumed directly by herbivores, but dies and enters these chains in the form of leaf litter, then undergoing decomposition and mineralization.
In aquatic ecosystems, most of the matter and energy is included in pasture chains, and in terrestrial ecosystems, detrital chains are most important.
Thus, at the level of consumers, the flow of organic matter is divided into different groups of consumers:
living organic matter follows grazing chains;
dead organic matter goes along detrital chains.
Living organisms require energy and nutrients to exist. Autotrophs transform the radiant energy of the Sun in the process of photosynthesis, synthesizing organic substances from carbon dioxide and water.
Heterotrophs use these organic substances in the process of nutrition, ultimately decomposing them again into carbon dioxide and water, and the energy accumulated in them is spent on various processes of the life of organisms. Thus, the light energy of the Sun turns into chemical energy of organic substances, and then into mechanical and thermal energy.
All living organisms in the ecological system can be divided into three functional groups according to the type of nutrition - producers, consumers, decomposers.
1. Producers- these are green autotrophic plants that produce organic substances from inorganic ones and are capable of accumulating solar energy.
2. Consumers- These are heterotrophic animals that consume ready-made organic substances. First order consumers can use organic matter from plants (herbivores). Heterotrophs that use animal food are divided into consumers of orders II, III, etc. (carnivores). All of them use the energy of chemical bonds stored in organic substances by producers.
3. Decomposers- These are heterotrophic microorganisms, fungi, that destroy and mineralize organic residues. Thus, decomposers, as it were, complete the cycle of substances, forming inorganic substances to enter a new cycle.
The sun provides a constant supply of energy, and living organisms eventually dissipate it as heat. During the life activity of organisms, a constant cycle of energy and substances occurs, and each species uses only part of the energy contained in organic substances. As a result, there are power circuit - trophic chains, food chains, representing a sequence of species that extract organic matter and energy from the original food substance, with each previous link becoming food for the next (Fig. 98).
Rice. 98. General diagram of the food chain
In each link, most of the energy is consumed in the form of heat and is lost, which limits the number of links in the chain. But most chains begin with a plant and end with a predator, and the largest one at that. Decomposers break down organic matter at every level and are the final link in the food chain.
Due to the decrease in energy at each level, there is a decrease in biomass. The trophic chain usually has no more than five levels and is an ecological pyramid, with a wide base at the bottom and tapering at the top (Fig. 99).
Rice. 99. Simplified diagram of the ecological pyramid of biomass (1) and pyramid of numbers (2)
Ecological pyramid rule reflects the pattern according to which in any ecosystem the biomass of each next link is 10 times less than the previous one.
There are three types of ecological pyramids:
A pyramid reflecting the number of individuals at each level of the food chain - pyramid of numbers;
Pyramid of biomass of organic matter synthesized at each level - mass pyramid(biomass);
- energy pyramid, showing the amount of energy flow. Typically the power chain consists of 3-4 links:
plant → hare → wolf;
plant → vole → fox → eagle;
plant → caterpillar → tit → hawk;
plant → gopher → viper → eagle.
However, in real conditions in ecosystems, various food chains intersect with each other, forming branched networks. Almost all animals, with the exception of rare specialized species, use a variety of food sources. Therefore, if one link in the chain falls out, there is no disruption to the system. The greater the species diversity and the richer the food webs, the more stable the biocenosis.
In biocenoses, two types of trophic networks are distinguished: pasture and detritus.
1. IN grassland type food web the flow of energy goes from plants to herbivores, and then to consumers of a higher order. This gorging network. Regardless of the size of the biocenosis and habitat, herbivorous animals (terrestrial, aquatic, soil) graze, eat up green plants and transfer energy to the next levels (Fig. 100).
Rice. 100. Pasture food network in a terrestrial biocenosis
2. If the flow of energy begins with dead plant and animal remains, excrement and goes to the primary detritivores - decomposers, partially decomposing organic matter, then such a trophic network is called detrital, or network of decomposition(Fig. 101). Primary detritivores include microorganisms (bacteria, fungi), small animals (worms, insect larvae).
Rice. 101. Detrital food chain
In terrestrial biogeocenoses, both types of trophic chain are present. In aquatic communities, the grazing chain predominates. In both cases, the energy is fully used.
Trophic chains form the basis of relationships in living nature, but food connections are not the only type of relationship between organisms. Some species can participate in the distribution, reproduction, settlement of other species, and create appropriate conditions for their existence. All the many and varied connections between living organisms and the environment ensure the existence of species in a stable, self-regulating ecosystem.
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§ 71. Ecological systems§ 73. Properties and structure of biocenoses