A food chain is a complex structure of links in which each of them is interconnected with a neighboring or some other link. These components of the chain are various groups of flora and fauna organisms.

In nature, the food chain is a way of moving matter and energy in the environment. All this is necessary for the development and "construction" of ecosystems. Trophic levels is a community of organisms that is located at a certain level.

Biotic cycle

The food chain is a biotic cycle that combines living organisms and components of inanimate nature. This phenomenon is also called biogeocenosis and includes three groups: 1. Producers. The group consists of organisms that produce food substances for other creatures through photosynthesis and chemosynthesis. The products of these processes are primary organic substances. Traditionally, producers are first in the food chain. 2. Consumers. The food chain places this group above the producers because they consume the nutrients produced by the producers. This group includes various heterotrophic organisms, for example, animals that eat plants. There are several subspecies of consumers: primary and secondary. Herbivores can be classified as primary consumers, and carnivores, which eat the previously described herbivores, can be classified as secondary consumers. 3. Reducers. This includes organisms that destroy all previous levels. A good example is when invertebrates and bacteria decompose plant remains or dead organisms. Thus, the food chain is completed, but the cycle of substances in nature continues, since as a result of these transformations, mineral and other useful substances are formed. In the future, the formed components are used by producers to form primary organics. The food chain is a complex structure, so secondary consumers can easily become food for other predators, which are classified as tertiary consumers.

Classification

thus, it is directly involved in the cycle of substances in nature. There are two types of chains: detrital and pasture. As can be seen from the names, the first group is most often found in forests, and the second - in open spaces: field, meadow, pasture.

Such a chain has a more complex structure of connections, it is even possible for the appearance of predators of the fourth order there.

pyramids

one or more, existing in a particular habitat, form the paths and directions of movement of substances and energy. All this, that is, organisms and their habitats, form a functional system, which is called an ecosystem (ecological system). Trophic connections are quite rarely straightforward, they usually look like a complex and intricate network in which each component is interconnected with the others. The interweaving of food chains forms food webs, which are mainly used to build and calculate ecological pyramids. At the base of each pyramid is the level of producers, on top of which all subsequent levels are adjusted. Distinguish a pyramid of numbers, energy and biomass.

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 the ecosystem, and first of all they are connected together by the flow of energy and the cycle of matter. The channels through which energy flows through the community are called food chains. The energy of a ray of sunlight falling on the tops of trees or on the surface of a pond is captured by green plants - whether they are huge trees or tiny algae - and used by them in the process of photosynthesis. This energy goes to the growth, development and reproduction of plants. Plants, as producers of organic matter, are called producers. Producers, in turn, serve as a source of energy for those who feed on 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 consumers of the second order. When moving from one link to another, energy is inevitably lost, so there are rarely more than 5-6 participants in the food chain. The decomposers complete the cycle - bacteria and fungi decompose animal corpses, plant remains, turning 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 the water necessary for photosynthesis. The food chain is a connected linear structure of links, each of which is connected with neighboring links by the relationship "food - consumer". 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 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 that occur by eating some organisms by others, energy is dissipated, part of which is converted into heat. With each next transition from one trophic link (step) to another, up to 80-90% of potential energy is lost. This limits the possible number of steps, or chain links, to usually four or five. The shorter the food chain, the more available energy is stored.

On average, 100 kg of the body of herbivores is formed from 1 thousand kg of plants. Predators eating 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 on phytoplankton that captures solar energy.

Thus, to build 1 kg of the 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 are a pyramid of numbers, reflecting the number of individuals at each stage of the food chain, a biomass pyramid - the amount of organic matter synthesized at each level, and an energy pyramid - the amount of energy in food. All of them have the same direction, differing in the absolute value of digital values. In real conditions, power chains can have a different number of links. In addition, food chains can cross over to form food networks. Almost all species of animals, with the exception of very specialized food, use more than one food source, but several). The greater the species diversity in the 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 at the beginning of the food chain there are always green plants, and at the end - predators. With each link in the chain, organisms become larger, they multiply more slowly, their number decreases. The species that occupy the position of the lower links, although they are 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 base for higher animals without any prospects for progressive evolution.

In any geological epoch, organisms that were at the highest level in food relationships evolved with the greatest speed, for example, in the Devonian - lobe fish - fish-eating predators; in the Carboniferous period - predatory stegocephals. In Permian - reptiles that hunted stegocephalians. Throughout the entire 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 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 more species, affect air movement, temperature, and illumination of the surrounding space. Examples of relationships that affect species habitats are numerous. Sea acorns are sessile marine crustaceans that often settle on the skin of whales. The larvae of many flies live in cow dung. A particularly large role in creating or changing the environment for other organisms belongs to plants. In thickets of plants, whether it is a forest or a meadow, the temperature fluctuates to a lesser extent than in open spaces, and the humidity is higher.
Often one species is involved in the distribution of another. Animals carry seeds, spores, plant pollen, as well as other smaller animals. Plant seeds can be captured by animals upon accidental contact, especially if the seeds or seedlings have special hooks, hooks (sequence, burdock). When eating fruits, berries that are not digestible, the seeds are excreted along with the droppings. Mammals, birds and insects carry numerous ticks on their bodies.

All these diverse connections provide the possibility of the existence of species in the 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 does not have a precursor, that is, organisms from this group do not use other organisms as food, being producers. Most often in this place there are plants, mushrooms, algae. Organisms of the last link in the chain do not act as food for other organisms.

Each organism has a certain reserve of energy, that is, we can say that each link in the chain has its own potential energy. In the process of eating, the potential energy of food passes to its consumer.

All species that make up the food chain subsist on the organic matter created by green plants. At the same time, there is an important regularity associated with the efficiency of the use and conversion of energy in the process of nutrition. Its essence is as follows.

In total, only about 1% of the radiant energy of the Sun incident on a plant is converted into the 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 life 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 less 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 - seals or predatory fish (lenok, taimen, adults of omul, etc.). Man participates in this chain as the last link, but he can consume the products of lower links, for example, fish or even invertebrates when using crustaceans, aquatic plants, etc. 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 associated with it by the relationship "food - consumer". So grass is eaten not only by cows, but also by other animals, and cows are food not only for humans. The establishment of such links turns the food chain into a more complex structure - food web.

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

Plants (algae) are the initial level (link) of any trophic (food) chain in a reservoir. Plants do not eat anyone (with the exception of a small number of species of insectivorous plants - sundew, butterflies, pemphigus, 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 herbivorous (pasture) animals. They are followed by small carnivores feeding on herbivores, then a link of larger predators. In the chain, each subsequent organism is larger than the previous one. Chains of predators contribute to the stability of the trophic chain.

The food chain of saprophytes is the closing link of the trophic chain. Saprophytes feed on dead organisms. Chemical substances formed during the decomposition of dead organisms are again consumed by plants - 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, conditioned by Nature for destruction).

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

herbivorous animals;


predators are carnivores;


omnivores, including humans.


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


The second trophic chain unites living beings that metabolize everything and everyone. This task is performed by reducers. 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 food chains - pasture and detrital.


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


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


CONCLUSION


All living organisms that inhabit our planet do not exist on their own, they depend on the environment and experience its effects. 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 various forms of organisms and the most diverse formation of their life.


The main function of the biosphere is to ensure the circulation 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 nourishment for others, i.e. connected with each other by energy relations. Nutritional connections in communities, they are mechanisms for transferring energy from one organism to another. In every community trophic connections are intertwined in a complex network.


Organisms of any species are potential food for many other species.


food webs in biocenoses are very complex, and it seems that the energy entering them can migrate from one organism to another for a long time. In fact, the path of each specific portion of the energy accumulated by green plants is short; it can be transmitted through no more than 4-6 links in a series consisting of sequentially feeding on each other organisms. Such rows, in which it is possible to trace the ways of spending the initial dose of energy, 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; carnivorous, living at the expense of herbivorous forms - to the third; those consuming other carnivores - to the fourth, and so on. Thus, consumers of the first, second and third orders are distinguished, occupying different levels in the food chains. Naturally, the main role is played by the food specialization of consumers. Species with a wide range of food are included in food chains at different trophic levels.


BIBLIOGRAPHY

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

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

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.

Target: expand knowledge of biotic environmental factors.

Equipment: herbarium plants, stuffed chordates (fish, amphibians, reptiles, birds, mammals), insect collections, animal wet preparations, illustrations of various plants and animals.

Working process:

1. Use the equipment and make up two power circuits. Remember that a chain always starts with a producer and ends with a decomposer.

Plants → insects→lizard → bacteria

Plants → grasshopper→ frog → bacteria

Recall your observations in nature and make two food chains. Sign producers, consumers (1st and 2nd orders), decomposers.

Violet → Springtails→predatory mites→carnivorous centipedes→ bacteria

Producer - consumer1 - consumer2 - consumer2 - decomposer

Cabbage→ slug→ frog →bacteria

Producer - consumer1 - consumer2 - decomposer

What is a food chain and what underlies it? What determines the stability of the biocenosis? Formulate a conclusion.

Conclusion:

food (trophic) chain- rows of species of plants, animals, fungi and microorganisms that are related to each other by relationships: food - consumer (a sequence of organisms in which there is a phased transfer of matter and energy from source to consumer). Organisms of the next link eat the organisms of the previous link, and thus a chain transfer of energy and matter is carried out, which underlies the cycle of substances in nature. With each transfer from link to link, a large part (up to 80-90%) of the potential energy is lost, dissipating in the form of heat. For this reason, the number of links (species) in the food chain is limited and usually does not exceed 4-5. The stability of the biocenosis is determined by the diversity of its species composition. Producers- organisms capable of synthesizing organic substances from inorganic, that is, all autotrophs. Consumers- heterotrophs, organisms that consume ready-made organic substances created by autotrophs (producers). Unlike reducers

Consumers are not able to decompose organic substances into inorganic ones. Decomposers- microorganisms (bacteria and fungi) that destroy the dead remains of living beings, turning them into inorganic and simple organic compounds.

3. Name the organisms that should be in the missing place of the following food chains.

1) Spider, fox

2) caterpillar tree eater, snake hawk

3) caterpillar

4. From the proposed list of living organisms, make a food web:

grass, berry bush, fly, titmouse, frog, snake, hare, wolf, decay bacteria, mosquito, grasshopper. Indicate the amount of energy that passes from one level to another.

1. Grass (100%) - grasshopper (10%) - frog (1%) - already (0.1%) - decay bacteria (0.01%).

2. Shrub (100%) - hare (10%) - wolf (1%) - decay bacteria (0.1%).

3. Grass (100%) - fly (10%) - titmouse (1%) - wolf (0.1%) - decay bacteria (0.01%).

4. Grass (100%) - mosquito (10%) - frog (1%) - already (0.1%) - decay bacteria (0.01%).

5. Knowing the rule of energy transfer from one trophic level to another (about 10%), build a biomass pyramid of the third food chain (task 1). Plant biomass is 40 tons.

Grass (40 tons) - grasshopper (4 tons) - sparrow (0.4 tons) - fox (0.04).

6. Conclusion: what do the rules of ecological pyramids reflect?

The rule of ecological pyramids very conditionally conveys the pattern of energy transfer from one level of nutrition to the next, in the food chain. For the first time, these graphic models were developed by C. Elton in 1927. According to this regularity, the total mass of plants should be an order of magnitude greater than that of herbivorous animals, and the total mass of herbivorous animals should be an order of magnitude greater than that of first-level predators, and so on. to the very end of the food chain.

Lab #1

In nature, any species, population, and even a single individual do not live in isolation from each other and their environment, but, on the contrary, experience numerous mutual influences. Biotic communities or biocenoses - communities of interacting living organisms, which are a stable system connected by numerous internal connections, with a relatively constant structure and an interdependent set of species.

Biocenosis is characterized by certain structures: species, spatial and trophic.

The organic components of the biocenosis are inextricably linked with the inorganic ones - soil, moisture, atmosphere, forming together with them a stable ecosystem - biogeocenosis .

Biogenocenosis- a self-regulating ecological system formed by populations of different species living together and interacting with each other and with inanimate nature in relatively homogeneous environmental conditions.

Ecological systems

Functional systems that include communities of living organisms of different species and their habitats. The connections between the components of the ecosystem arise, first of all, on the basis of food relationships and ways of obtaining energy.

Ecosystem

A set of species of plants, animals, fungi, microorganisms interacting with each other and with the environment in such a way that such a community can be preserved and function for an indefinitely long time. Biotic community (biocenosis) consists of a community of plants ( phytocenosis), animals ( zoocenosis), microorganisms ( microbiocenosis).

All organisms of the Earth and their habitat also represent an ecosystem of the highest rank - biosphere , which has stability and other properties of the ecosystem.

The existence of an ecosystem is possible due to the constant influx of energy from the outside - such an energy source, as a rule, is the sun, although this is not true for all ecosystems. The stability of an ecosystem is ensured by direct and feedback links between its components, the internal circulation of substances and participation in global cycles.

The doctrine of biogeocenoses developed by V.N. Sukachev. The term " ecosystem"Introduced into use by the English geobotanist A. Tensley in 1935, the term" biogeocenosis"- Academician V.N. Sukachev in 1942 biogeocenosis it is necessary to have a plant community (phytocenosis) as the main link, which ensures the potential immortality of biogeocenosis due to the energy produced by plants. ecosystems may not contain phytocenosis.

Phytocenosis

A plant community that has historically developed as a result of a combination of interacting plants in a homogeneous area.

He is characterized:

- a certain species composition,

- life forms

- tiered (aboveground and underground),

- abundance (frequency of occurrence of species),

- accommodation,

- aspect (appearance),

- vitality

- seasonal changes,

- development (change of communities).

Layered (number of floors)

One of the characteristic features of the plant community, which consists, as it were, in its floor-by-floor division both in the above-ground and in the underground space.

Aboveground layering allows better use of light, and underground - water and minerals. Usually, up to five tiers can be distinguished in the forest: the upper (first) - tall trees, the second - low trees, the third - shrubs, the fourth - grasses, the fifth - mosses.

Underground layering - a mirror reflection of the aboveground: the roots of trees go deepest of all, underground parts of mosses are located near the surface of the soil.

According to the method of obtaining and using nutrients All organisms are divided into autotrophs and heterotrophs. In nature, there is a continuous circulation of biogenic substances necessary for life. Chemical substances are extracted by autotrophs from the environment and returned to it through heterotrophs. This process takes on very complex forms. Each species uses only a part of the energy contained in organic matter, bringing its decay to a certain stage. Thus, in the process of evolution, ecological systems have developed chains and power supply .

Most biogeocenoses have a similar trophic structure. The basis of them are green plants - producers. Herbivorous and carnivorous animals are necessarily present: consumers of organic matter - consumers and destroyers of organic residues - decomposers.

The number of individuals in the food chain consistently decreases, the number of victims is greater than the number of their consumers, since in each link of the food chain, with each transfer of energy, 80-90% of it is lost, dissipating in the form of heat. Therefore, the number of links in the chain is limited (3-5).

Species diversity of biocenosis It is represented by all groups of organisms - producers, consumers and decomposers.

Any link broken in the food chain causes a violation of the biocenosis as a whole. For example, deforestation leads to a change in the species composition of insects, birds, and, consequently, animals. On a treeless site, other food chains will develop and another biocenosis will form, which will take more than a dozen years.

Food chain (trophic or food )

Interrelated species that sequentially extract organic matter and energy from the original food substance; moreover, each previous link in the chain is food for the next one.

Food chains in each natural area with more or less homogeneous conditions of existence are composed of complexes of interconnected species that feed on each other and form a self-sustaining system in which the circulation of substances and energy is carried out.

Ecosystem components:

- Producers - autotrophic organisms (mainly green plants) are the only producers of organic matter on Earth. Energy-rich organic matter in the process of photosynthesis is synthesized from energy-poor inorganic substances (H 2 0 and CO 2).

- Consumers - herbivorous and carnivorous animals, consumers of organic matter. Consumers can be herbivores when they use producers directly, or carnivores when they feed on other animals. In the food chain, they most often have serial number from I to IV.

- decomposers - heterotrophic microorganisms (bacteria) and fungi - destroyers of organic residues, destructors. They are also called the orderlies of the Earth.

Trophic (food) level - a set of organisms united by the type of food. The idea of ​​the trophic level allows us to understand the dynamics of energy flow in an ecosystem.

1. the first trophic level is always occupied by producers (plants),
2. the second - consumers of the first order (herbivorous animals),
3. the third - consumers of the second order - predators that feed on herbivorous animals),
4. the fourth - consumers of the III order (secondary predators).

There are the following types food chains:

AT pasture chain (eating chains) green plants are the main source of food. For example: grass -> insects -> amphibians -> snakes -> birds of prey.

- detritus chains (decomposition chains) begin with detritus - dead biomass. For example: leaf litter -> earthworms -> bacteria. A feature of detrital chains is also that in them plant products are often not consumed directly by herbivorous animals, but die off and are mineralized by saprophytes. Detrital chains are also characteristic of ecosystems of the ocean depths, the inhabitants of which feed on dead organisms that have descended from the upper layers of the water.

Relationships between species in ecological systems that have developed in the process of evolution, in which many components feed on different objects and themselves serve as food for various members of the ecosystem. Simplified, the food web can be represented as intertwining food chains.

Organisms of different food chains that receive food through an equal number of links in these chains are on one trophic level. At the same time, different populations of the same species included in different food chains can be located on different trophic levels. The ratio of different trophic levels in an ecosystem can be represented graphically as ecological pyramid.

ecological pyramid

A way to graphically display the ratio of different trophic levels in an ecosystem - there are three types:

The abundance pyramid reflects the abundance of organisms at each trophic level;

The biomass pyramid reflects the biomass of each trophic level;

The energy pyramid shows the amount of energy that has passed through each trophic level in a given amount of time.

Ecological pyramid rule

A pattern that reflects a progressive decrease in the mass (energy, number of individuals) of each subsequent link in the food chain.

Pyramid of numbers

An ecological pyramid showing the number of individuals at each food level. The pyramid of numbers does not take into account the size and weight of individuals, life expectancy, metabolic rate, but the main trend is always traced - a decrease in the number of individuals from link to link. For example, in the steppe ecosystem, the number of individuals is distributed as follows: producers - 150000, herbivorous consumers - 20000, carnivorous consumers - 9000 ind./ar. The meadow biocenosis is characterized by the following number of individuals on an area of ​​4000 m 2: producers - 5,842,424, herbivorous consumers of the 1st order - 708,624, carnivorous consumers of the 2nd order - 35,490, carnivorous consumers of the 3rd order - 3.

Biomass pyramid

The pattern according to which the amount of plant matter that serves as the basis of the food chain (producers) is approximately 10 times greater than the mass of herbivores (consumers of the 1st order), and the mass of herbivores is 10 times greater than the mass of carnivores (consumers of the 2nd order), t i.e. each subsequent food level has a mass 10 times less than the previous one. On average, out of 1000 kg of plants, 100 kg of the body of herbivores is formed. Predators eating herbivores can build 10 kg of their biomass, secondary predators - 1 kg.

energy pyramid

expresses a pattern according to which the flow of energy gradually decreases and depreciates in the transition from link to link in the food chain. So, in the biocenosis of the lake, green plants - producers - create a biomass containing 295.3 kJ / cm 2, consumers of the first order, consuming plant biomass, create their own biomass containing 29.4 kJ / cm 2; consumers of the second order, using consumers of the first order for food, create their own biomass containing 5.46 kJ / cm 2. The loss of energy during the transition from consumers of the 1st order to consumers of the 2nd order, if they are warm-blooded animals, increases. This is explained by the fact that in these animals a lot of energy is spent not only on building their biomass, but also on maintaining a constant body temperature. If we compare the cultivation of a calf and a perch, then the same amount of food energy expended will give 7 kg of beef and only 1 kg of fish, since the calf feeds on grass, and the predatory perch feeds on fish.

Thus the first two types of pyramids have a number of significant drawbacks:

The biomass pyramid reflects the state of the ecosystem at the time of sampling and therefore shows the ratio of biomass in this moment and does not reflect the productivity of each trophic level (i.e., its ability to form biomass for a certain period of time). Therefore, when fast-growing species are among the producers, the biomass pyramid may turn upside down.

The energy pyramid allows you to compare the productivity of different trophic levels, since it takes into account the time factor. In addition, it takes into account the difference in the energy value of various substances (for example, 1 g of fat provides almost twice as much energy as 1 g of glucose). Therefore, the pyramid of energy always tapers upward and is never inverted.

Ecological plasticity

The degree of endurance of organisms or their communities (biocenoses) to the effects of environmental factors. Ecologically plastic species have a wide range of reaction rate , i.e., widely adapted to different habitats (stickleback and eel fish, some protozoa live in both fresh and salt waters). Highly specialized species can exist only in a certain environment: marine animals and algae - in salt water, river fish and lotus plants, water lilies, duckweed live only in fresh water.

Generally ecosystem (biogeocenosis) characterized by the following indicators:

species diversity,

Density of species populations,

Biomass.

Biomass

The total amount of organic matter of all individuals of a biocenosis or species with energy contained in it. Biomass is usually expressed in units of mass in terms of dry matter per unit area or volume. Biomass can be determined separately for animals, plants or individual species. So, the biomass of fungi in the soil is 0.05-0.35 t / ha, algae - 0.06-0.5, roots of higher plants - 3.0-5.0, earthworms - 0.2-0.5 , vertebrates - 0.001-0.015 t/ha.

In biogeocenoses there are primary and secondary biological productivity :

ü Primary biological productivity of biocenoses- the total total productivity of photosynthesis, which is the result of the activity of autotrophs - green plants, for example, a 20-30-year-old pine forest produces 37.8 t / ha of biomass per year.

ü Secondary biological productivity of biocenoses- the total total productivity of heterotrophic organisms (consumers), which is formed through the use of substances and energy accumulated by producers.

Populations. Structure and population dynamics.

Each species on Earth occupies a certain range because it can exist only under certain environmental conditions. However, the habitat conditions within the range of one species can differ significantly, which leads to the disintegration of the species into elementary groups of individuals - populations.

population

A set of individuals of the same species occupying a separate territory within the range of the species (with relatively homogeneous habitat conditions), freely interbreeding with each other (having a common gene pool) and isolated from other populations of a given species, possessing all the necessary conditions to maintain their stability for a long time in changing environmental conditions. The most important characteristics populations are its structure (age, sex composition) and population dynamics.

Under the demographic structure populations understand its sex and age composition.

Spatial structure populations are the features of the distribution of individuals of a population in space.

Age structure population is related to the ratio of individuals of different ages in the population. Individuals of the same age are combined into cohorts - age groups.

AT age structure of plant populations allocate next periods:

Latent - the state of the seed;

Pregenerative (includes the states of a seedling, juvenile plant, immature and virginal plants);

Generative (usually divided into three sub-periods - young, mature and old generative individuals);

Post-generative (includes the states of subsenile, senile plants and the dying phase).

Belonging to a certain age state is determined by biological age- the degree of expression of certain morphological (for example, the degree of dissection of a complex leaf) and physiological (for example, the ability to give offspring) signs.

In animal populations, one can also distinguish various age stages. For example, insects that develop with complete metamorphosis go through the following stages:

larvae,

pupae,

Imago (adult insect).

The nature of the age structure of the populationdepends on the type of survival curve characteristic of a given population.

survival curvereflects the mortality rate in different age groups and is a declining line:

1. If the mortality rate does not depend on the age of individuals, the death of individuals occurs evenly in this type, the mortality rate remains constant throughout life ( type I ). Such a survival curve is characteristic of species whose development occurs without metamorphosis with sufficient stability of the born offspring. This type is called type of hydra- it has a survival curve approaching a straight line.
2. In species for which the role of external factors in mortality is small, the survival curve is characterized by a slight decrease until a certain age, after which there is a sharp drop due to natural (physiological) mortality ( type II ). The nature of the survival curve close to this type is characteristic of humans (although the human survival curve is somewhat flatter and is somewhere between types I and II). This type is called Drosophila type: this is what Drosophila demonstrates in laboratory conditions (not eaten by predators).
3. Many species are characterized by high mortality in the early stages of ontogeny. In such species, the survival curve is characterized by a sharp drop in the region of younger ages. Individuals that have survived the “critical” age demonstrate low mortality and survive to older ages. The type is named oyster type (type III ).

Sex structure populations

The sex ratio is directly related to the reproduction of the population and its sustainability.

There are primary, secondary and tertiary sex ratio in the population:

- Primary sex ratio determined by genetic mechanisms - the uniformity of the divergence of the sex chromosomes. For example, in humans, XY chromosomes determine the development of the male sex, and XX - the female. In this case, the primary sex ratio is 1:1, i.e., equally likely.

- Secondary sex ratio - this is the sex ratio at the time of birth (among newborns). It can differ significantly from the primary one for a number of reasons: the selectivity of eggs for spermatozoa carrying the X- or Y-chromosome, the unequal ability of such spermatozoa to fertilize, and various external factors. For example, zoologists have described the effect of temperature on the secondary sex ratio in reptiles. A similar pattern is characteristic of some insects. So, in ants, fertilization is ensured at temperatures above 20 ° C, and unfertilized eggs are laid at lower temperatures. Males hatch from the latter, and mostly females from the fertilized ones.

- Tertiary sex ratio - sex ratio among adult animals.

Spatial structure populations reflects the nature of the distribution of individuals in space.

Allocate three main types of distribution of individuals in space:

- uniform or uniform(individuals are evenly distributed in space, at equal distances from each other); occurs rarely in nature and is most often caused by acute intraspecific competition (for example, in predatory fish);

- congregational or mosaic(“spotted”, individuals are located in isolated clusters); occurs much more frequently. It is associated with the characteristics of the microenvironment or the behavior of animals;

- random or diffuse(individuals are randomly distributed in space) - can be observed only in a homogeneous environment and only in species that do not show any desire to unite in groups (for example, in a beetle in flour).

Population size denoted by the letter N. The ratio of the increase N to the unit time dN / dt expressesinstantaneous speedchanges in population size, i.e. change in population at time t.Population Growthdepends on two factors - fertility and mortality, provided there is no emigration and immigration (such a population is called isolated). The difference between birth rate b and death rate d and isisolated population growth rate:

Population stability

This is its ability to be in a state of dynamic (i.e., mobile, changing) equilibrium with the environment: environmental conditions change - the population also changes. One of the most important conditions for sustainability is internal diversity. In relation to a population, these are mechanisms for maintaining a certain population density.

Allocate three types of dependence of population size on its density .

First type (I) - the most common, characterized by a decrease in population growth with an increase in its density, which is provided by various mechanisms. For example, many species of birds are characterized by a decrease in fertility (fertility) with an increase in population density; an increase in mortality, a decrease in the resistance of organisms with an increased population density; change in the age of onset of puberty depending on the density of the population.

The third type ( III ) characteristic of populations in which the “group effect” is noted, i.e. a certain optimal population density contributes to better survival, development, and vital activity of all individuals, which is inherent in most group and social animals. For example, for the resumption of populations of heterosexual animals, at least a density is needed that provides a sufficient probability of meeting a male and a female.

Thematic tasks

A1. Biogeocenosis is formed

1) plants and animals

2) animals and bacteria

3) plants, animals, bacteria

4) territory and organisms

A2. Consumers of organic matter in forest biogeocenosis are

1) spruce and birch

2) mushrooms and worms

3) hares and squirrels

4) bacteria and viruses

A3. The producers in the lake are

2) tadpoles

A4. The process of self-regulation in biogeocenosis affects

1) sex ratio in populations of different species

2) the number of mutations that occur in populations

3) predator-prey ratio

4) intraspecific competition

A5. One of the conditions for the sustainability of an ecosystem can be

1) her ability to change

2) variety of species

3) fluctuations in the number of species

4) the stability of the gene pool in populations

A6. Reducers are

2) lichens

4) ferns

A7. If the total mass received by a consumer of the 2nd order is 10 kg, then what was the total mass of producers that became a source of food for this consumer?

A8. Specify the detrital food chain

1) fly - spider - sparrow - bacteria

2) clover - hawk - bumblebee - mouse

3) rye - titmouse - cat - bacteria

4) mosquito - sparrow - hawk - worms

A9. The initial source of energy in the biocenosis is energy

1) organic compounds

2) inorganic compounds

4) chemosynthesis

1) hares

2) bees

3) blackbirds

4) wolves

A11. In one ecosystem you can find oak and

1) gopher

3) lark

4) blue cornflower

A12. Power networks are:

1) relationships between parents and offspring

2) family (genetic) ties

3) metabolism in the cells of the body

4) ways of transferring substances and energy in an ecosystem

A13. The ecological pyramid of numbers reflects:

1) the ratio of biomass at each trophic level

2) the ratio of the masses of an individual organism at different trophic levels

3) food chain structure

4) diversity of species at different trophic levels