Any living organism chooses the conditions that are most favorable for its habitat and provide it with the opportunity to eat fully. The fox chooses a place to live where many hares live. The lion settles closer to the herds of antelope. The sticky fish not only travels attached to the shark, but also eats with it.

Plants, although they are deprived of the opportunity to consciously choose their habitat, mostly grow in the places that are most comfortable for themselves. Gray alder is often accompanied by nettles, which require nitrogen nutrition. The fact is that alder cohabits with bacteria that enrich the soil with nitrogen.

The food web is a kind of symbiosis

Here we are faced with a certain type of relationship. It's about about the so-called symbiosis. It is a direct relationship in which both organisms benefit. They are also called food webs and chains. Both terms have similar meanings.

How are food chains and food webs different from each other? Separate groups of organisms (fungi, plants, bacteria, animals) constantly exchange certain substances and energy with each other. This process is called the food chain. Exchange between groups occurs when some eat others. The process of interaction between such chains is called a food web.

How organisms are interconnected

It is known that leguminous plants(clover, mouse peas, caraganas) coexist with tuber bacteria that convert nitrogen into forms that are absorbed by plants. In turn, bacteria receive the organic substances they need from plants.

Many of the relationships described are of a specific nature. However, in every biocenosis there are relationships in which each population takes part. These are nutritional or trophic (trophos - food) relationships.

Examples of food webs and chains:

In all cases, the organism that feeds on others derives a one-sided benefit. By participating in the feeding process, all individuals of the population provide themselves with the energy and various substances necessary for their life. The population that serves as food is negatively affected by the predators that devour it.

Autotrophs and heterotrophs

Let us remember that according to the way they feed, organisms are divided into two groups.

Autotrophic (autos - self) organisms live off an inorganic source of hydrocarbons. This group includes plants.

Heterotrophic (heteros - other) organisms live off an organic source of hydrocarbons. This group includes fungi and bacteria. If autotrophs are independent of other organisms as a source of carbon and energy, then heterotrophs in this regard are completely dependent on plants.

Competitive relations between groups

Relationships that lead to oppression of one of the partners are not necessarily related to nutritional relationships. Many weeds produce metabolites that inhibit plant growth. Dandelion, wheatgrass, and cornflower have a depressing effect on oats, rye and other cultivated grains.

In each biocenosis, populations of many species live, and the relationships between them are diverse. We can say that the population is limited in its capabilities by these relationships and must find a place that is unique to it.

Habitat availability level environmental resources determines the possibility of the existence of many niches. The number of species populations forming the biocenosis also depends on this. In the favorable climate of the steppes, biocenoses are formed consisting of hundreds of species, and in the tropical climate of forests - of thousands of species of organisms. Desert biocenoses in hot climates number several dozen species.

The spatial distribution of populations is equally variable. Tropical forests are multi-tiered, and living organisms fill the entire volume of space. In deserts, biocenoses are simple in structure, and populations are small. Thus, it is clear that the joint life of organisms in biocenoses is unusually complex. And yet, plants and animals, fungi and bacteria are united in biocenoses and exist only in their composition. What are the reasons for this?

The most important of them is the need of living organisms for nutrition and trophic dependence on each other.

In nature, any species, population and even individual do not live in isolation from each other and their habitat, 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 living together and interacting with each other and with inanimate nature different types under relatively homogeneous environmental conditions.

Ecological systems

Functional systems, including communities of living organisms of different species and their habitat. Connections between ecosystem components arise primarily on the basis of food relationships and methods of obtaining energy.

Ecosystem

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

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

The existence of an ecosystem is possible thanks to a constant flow of energy from the outside - such an energy source is usually the sun, although this is not true for all ecosystems. Ecosystem sustainability is ensured by direct and feedback 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. Tansley 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, ensuring the potential immortality of the biogeocenosis due to the energy generated by plants. Ecosystems may not contain phytocenosis.

Phytocenosis

A plant community formed historically as a result of a combination of interacting plants in a homogeneous area of ​​territory.

He is characterized:

- a certain species composition,

- life forms,

- tiering (aboveground and underground),

- abundance (frequency of occurrence of species),

- accommodation,

- aspect (appearance),

- vitality,

- seasonal changes,

- development (change of communities).

Tiering (number of floors)

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

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

Underground tiering - a mirror image of the above-ground: the roots of trees go deepest, the underground parts of mosses are located near the surface of the soil.

By method of receipt and use nutrients all organisms are divided into autotrophs and heterotrophs. In nature there is a continuous cycle of nutrients necessary for life. Chemical substances are extracted by autotrophs from environment and through heterotrophs they return to it again. This process takes very complex forms. Each species uses only part of the energy contained in organic matter, bringing its decomposition to a certain stage. Thus, in the process of evolution in ecological systems have developed chains And power supply network .

Most biogeocenoses have similar trophic structure. They are based on green plants - producers. Herbivores and carnivores 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 represented by all groups of organisms - producers, consumers and decomposers.

Violation of any link in the food chain causes disruption of the biocenosis as a whole. For example, deforestation leads to a change in the species composition of insects, birds, and, consequently, animals. In a treeless area, other food chains will develop and a different biocenosis will form, which will take several decades.

Food chain (trophic or food )

Interconnected species that successively extract organic matter and energy from the original nutrient; Moreover, each previous link in the chain is food for the next one.

The 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 occurs.

Ecosystem components:

- Producers - autotrophic organisms (mostly green plants) are the only producers of organic matter on Earth. Energy-rich organic matter is synthesized from energy-poor organic matter during photosynthesis inorganic substances(H 2 0 and C0 2).

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

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

Trophic (food) level - a set of organisms united by a type of nutrition. The concept 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. second - consumers of the first order (herbivorous animals),
3. third - consumers of the second order - predators that feed on herbivorous animals),
4. fourth - consumers III order(secondary predators).

The following types are distinguished: food chains:

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

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

The relationships between species in ecological systems that have developed during the process of evolution, in which many components feed on different objects and themselves serve as food for various members of the ecosystem. In simple terms, a food web can be represented as intertwined food chain system.

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

Ecological pyramid

A method of graphically displaying the relationship between different trophic levels in an ecosystem - there are three types:

The population pyramid reflects the number of organisms at each trophic level;

The biomass pyramid reflects the biomass of each trophic level;

The energy pyramid shows the amount of energy passing through each trophic level over a specified period of time.

Ecological pyramid rule

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

Number pyramid

An ecological pyramid showing the number of individuals at each nutritional level. The pyramid of numbers does not take into account the size and mass of individuals, life expectancy, metabolic rate, but the main trend is always visible - a decrease in the number of individuals from link to link. For example, in a steppe ecosystem the number of individuals is distributed as follows: producers - 150,000, herbivorous consumers - 20,000, carnivorous consumers - 9,000 individuals/area. The meadow biocenosis is characterized by the following number of individuals on an area of ​​4000 m2: producers - 5,842,424, herbivorous consumers of the first order - 708,624, carnivorous consumers of the second order - 35,490, carnivorous consumers of the third 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 herbivorous animals (consumers of the first order), and the mass of herbivorous animals is 10 times greater than that of carnivores (consumers of the second order), t That is, each subsequent food level has a mass 10 times less than the previous one. On average, 1000 kg of plants produce 100 kg of herbivore body. Predators that eat herbivores can build 10 kg of their biomass, secondary predators - 1 kg.

Pyramid of Energy

expresses a pattern according to which the flow of energy gradually decreases and depreciates when moving from link to link in the food chain. Thus, 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; Second order consumers, using first order consumers for food, create their own biomass containing 5.46 kJ/cm2. The loss of energy during the transition from consumers of the first order to consumers of the second order, if these are warm-blooded animals, increases. This is explained by the fact that these animals spend a lot of energy not only on building their biomass, but also on maintaining a constant body temperature. If we compare the raising of a calf and a perch, then the same amount of food energy expended will yield 7 kg of beef and only 1 kg of fish, since the calf eats grass, and the predatory perch eats fish.

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

The biomass pyramid reflects the state of the ecosystem at the time of sampling and therefore shows the ratio of biomass at a given moment and does not reflect the productivity of each trophic level (i.e. its ability to produce biomass over a certain period of time). Therefore, in the case when the number of producers includes fast-growing species, the biomass pyramid may turn out to be inverted.

The energy pyramid allows you to compare the productivity of different trophic levels because it takes into account the time factor. In addition, it takes into account the difference in energy value 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 narrows upward and is never inverted.

Ecological plasticity

The degree of endurance of organisms or their communities (biocenoses) to the influence of environmental factors. Ecologically plastic species have a wide range of reaction norm , i.e. widely adapted to different environments habitat (fish stickleback and eel, 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 the 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 defined separately for animals, plants or individual species. Thus, 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 , vertebrate animals - 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, Pine forest 20-30 years of age 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 dynamics of numbers.

Each species on Earth occupies a specific range, since it is able to exist only in certain environmental conditions. However, living 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 living conditions), freely interbreeding with each other (having a common gene pool) and isolated from other populations of this species, possessing all necessary conditions to maintain its stability for a long time in changing environmental conditions. The most important characteristics population 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 characteristics of the distribution of individuals in a population in space.

Age structure population is associated with the ratio of individuals of different ages in the population. Individuals of the same age are grouped into cohorts - age groups.

IN age structure of plant populations allocate following periods:

Latent - state of the seed;

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

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

Postgenerative (includes the states of subsenile, senile plants and the dying phase).

Belonging to a certain age condition 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 birth) characteristics.

In animal populations it is also possible to distinguish different age stages. For example, insects developing with complete metamorphosis go through the stages:

Larvae,

dolls,

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 decreasing line:

1. If the mortality rate does not depend on the age of individuals, the death of individuals occurs evenly in a given 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 usually called type of hydra- it is characterized by 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 something between types I and II). This type is called Drosophila type: This is what fruit flies demonstrate in laboratory conditions (not eaten by predators).
3. Many species are characterized by high mortality in the early stages of ontogenesis. In such species, the survival curve is characterized by a sharp drop in the region younger ages. Individuals that survive the “critical” age exhibit low mortality and live to older ages. The type is called type of oyster (type III ).

Sexual structure populations

Sex ratio has a direct bearing on population reproduction and sustainability.

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

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

- Secondary sex ratio 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 to sperm carrying the X- or Y-chromosome, the unequal ability of such sperm to fertilize, different external factors. For example, zoologists have described the effect of temperature on the secondary sex ratio in reptiles. A similar pattern is typical for some insects. Thus, in ants, fertilization is ensured at temperatures above 20 ° C, and at more low temperatures unfertilized eggs are laid. The latter hatch into males, and those that are fertilized predominantly into females.

- Tertiary sex ratio - sex ratio among adult animals.

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

Highlight three main types of distribution of individuals in space:

- uniform or uniform(individuals are distributed evenly in space, at equal distances from each other); is rare 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 often. It is associated with the characteristics of the microenvironment or behavior of animals;

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

Population size denoted by the letter N. The ratio of the increase in N to a unit of time dN / dt expressesinstantaneous speedchanges in population size, i.e. change in number at time t.Population growthdepends on two factors - fertility and mortality in the absence of emigration and immigration (such a population is called isolated). The difference between the birth rate b and death rate d 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, and the population also changes. One of the most important conditions sustainability is internal diversity. In relation to a population, these are mechanisms for maintaining a certain population density.

Highlight 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 ensured by various mechanisms. For example, many bird species are characterized by a decrease in fertility (fertility) with increasing population density; increased mortality, decreased resistance of organisms with increased population density; change in age at puberty depending on population density.

Third type ( III ) is characteristic of populations in which a “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, to renew populations of heterosexual animals, at a minimum, a density is required that provides a sufficient probability of meeting a male and a female.

Thematic assignments

A1. Biogeocenosis 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. 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 occurring 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) stability of the gene pool in populations

A6. Decomposers include

2) lichens

4) ferns

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

A8. Indicate the detrital food chain

1) fly – spider – sparrow – bacteria

2) clover – hawk – bumblebee – mouse

3) rye – tit – cat – bacteria

4) mosquito - sparrow - hawk - worms

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

1) organic compounds

2) inorganic compounds

4) chemosynthesis

1) hares

2) bees

3) fieldfare thrushes

4) wolves

A11. In one ecosystem you can find oak and

1) gopher

3) lark

4) blue cornflower

A12. Power networks are:

1) connections between parents and offspring

2) family (genetic) connections

3) metabolism in body cells

4) ways of transferring substances and energy in the 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) structure of the food chain

4) diversity of species at different trophic levels

The transfer of food energy from its source - autotrophs (plants) - through a number of organisms, occurring by eating some organisms by others, is called food chain .

With each successive transfer, most of the potential energy (80÷90%) is lost, turning into heat. Therefore, the shorter the food chain (the closer the organism is to its beginning - solar energy), the greater the amount of energy available to the population.

Food chains can be divided into two main types: pasture chain , which begins with a green plant and goes further to grazing herbivores and their predators, and detrital chain , which goes from dead organic matter to microorganisms, and then to detritivores and their predators. Food chains are not isolated from one another, but are closely intertwined with each other, forming the so-called food webs .

Pasture

Sunny Herbivorous Predators

Detrital

Detritus consumers Predators

The most simplified grazing and detrital food chains are combined into a food web in the form of a Y-shaped or two-channel energy flow diagram.

The magnitudes of those parts of energy clean products, which flow along two paths, are different in different types of ecosystems and often vary between seasons or years in the same ecosystem. In some shallow waters and intensively used pastures and steppes, 50% or more of the net product may flow through the pasture chain. In contrast, coastal marshes, oceans, forests, and most natural ecosystems function as detrital systems; in them, 90% or more percent of autotrophic products are consumed by heterotrophs only after the leaves, stems and other parts of the plants die and undergo “processing”, turning into dispersed or dissolved organic matter entering the water, bottom sediments and soil. This delayed consumption increases the structural complexity, as well as the storage and buffering capacity of ecosystems.

The close connection of the pasture and detrital food chains leads to the fact that when the level of energy impact from the outside on the ecosystem changes, flows quickly switch between channels, which allows maintaining the stability of ecosystems. Not all food eaten by grazing animals is digested: some of it, for example through feces, goes into the detritus chain.

The degree of influence of herbivores on a community depends not only on the amount of food energy assimilated by them, but also on the rate of removal of living plants. Direct removal by herbivores or humans of more than 30-50% of the annual growth of terrestrial vegetation reduces the ability of the ecosystem to resist stress. Overgrazing livestock was one of the reasons for the decline of many civilizations. " Undergrazing" can also be harmful. If direct consumption of living plants is completely absent, then detritus can accumulate faster than its decomposition by microorganisms. This slows down the circulation of minerals, and, in addition, the system can become a fire hazard.

In complex natural communities, organisms that receive their energy from the Sun through the same number of steps are considered to belong to the same trophic level . Thus, green plants occupy the first trophic level (level of producers), herbivores occupy the second (level of primary consumers), primary predators that eat herbivores occupy the third (level of secondary consumers), and secondary predators occupy the fourth (level of tertiary consumers). This trophic classification refers to functions rather than species per se. A population of a given species can occupy one or more trophic levels, depending on what energy sources it uses. Energy flow through a trophic level equals total assimilation ( A) at this level, which in turn is equal to production ( R) biomass plus respiration ( R):

A=P+R.

When energy is transferred between trophic levels, some potential energy is lost. First of all, the plant captures only a small fraction of the incoming sunlight energy (about 1%). Therefore, the number of consumers (for example, people) that can live for a given output of primary production depends strongly on the length of the food chain; each subsequent step in our traditional agricultural food chain reduces available energy by about an order of magnitude (i.e., a factor of 10). Therefore, if the meat content in the diet increases, the number of people who can be fed decreases.

The efficiency of the i-th trophic level is usually assessed as the ratio A i/ A i-1 , where A i – assimilation i th trophic level. For the first (autotrophic) trophic level it is 1-5%, for subsequent ones – 10-20%.

The low efficiency of natural ecosystems compared to the high efficiency of electric motors and other engines may be puzzling. But in fact, long-lived, large-scale ecosystems cannot be equated in this respect with short-lived mechanical systems. Firstly, in living systems a lot of “fuel” is spent on “repair” and self-maintenance, and when calculating the efficiency of engines, depreciation and energy costs for repairs are not taken into account. Second, under certain conditions, rapid growth that increases energy consumption may have higher value

for survival than maximizing the energy efficiency of food or fuel.

It is important for ecosystems to understand that any increase in their efficiency by artificial means will result in an increase in the costs of maintaining it. There always comes a limit, after which the gains from increased efficiency are negated by increased costs, not to mention the fact that the system can enter a dangerous oscillatory state that threatens destruction. Industrialized ecosystems may have already reached a stage where increasing costs lead to ever smaller returns. So, green plants are the basis of food chains. Both insects and vertebrates feed on green plants, which, in turn, serve as a source of energy and matter for building the body of consumers of the second, third, etc. orders of magnitude. General pattern

is that the number of individuals included in the food chain in each link consistently decreases and the number of victims is significantly greater than the number of their consumers. This happens because in each link of the food chain, at each stage of energy transfer, 80-90% of it is lost, dissipating in the form of heat. This circumstance limits the number of chain links (usually there are from 3 to 5). 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, 4 while secondary predators can build only 1 kg. Consequently, living biomass in each subsequent link of the chain progressively decreases. This pattern is called the Rules of the Ecological Pyramid 5.

IV. Relationships between organisms

Among the huge variety of relationships among living beings, certain types of relationships are distinguished that have much in common among organisms of different systematic groups.

1.Symbiosis

Symbiosis 1 - cohabitation (from the Greek sim - together, bios - life) is a form of relationship from which both partners or at least one benefit.

Symbiosis is divided into mutualism, protocooperation and commensalism.

Mutualism 2 - a form of symbiosis in which the presence of each of the two species becomes obligatory for both, each of the cohabitants receives relatively equal benefits, and the partners (or one of them) cannot exist without each other.

A typical example of mutualism is the relationship between termites and flagellated protozoa that live in their intestines. Termites eat wood, but they do not have enzymes to digest cellulose. Flagellates produce such enzymes and convert fiber into sugars. Without protozoa - symbionts - termites die of starvation. In addition to a favorable microclimate, the flagellates themselves receive food and conditions for reproduction in the intestines.

Protocooperation 3 - a form of symbiosis in which coexistence is beneficial to both species, but not necessarily to them. In these cases, there is no connection between this particular pair of partners.

Commensalism - a form of symbiosis in which one of the cohabiting species receives some benefit without bringing any harm or benefit to the other species.

Commensalism, in turn, is subdivided into tenantry, co-feeding, and freeloading.

"Tenancy" 4 - a form of commensalism in which one species uses another (its body or its home) as a shelter or home. Of particular importance is the use of reliable shelters for the preservation of eggs or juveniles.

The freshwater bitterling lays its eggs in the mantle cavity of bivalve mollusks - toothless. The laid eggs develop in ideal conditions supply of clean water.

"Companionship" 5 - a form of commensalism in which several species consume different substances or parts of the same resource.

"Freeloading" 6 - a form of commensalism in which one species consumes the food scraps of another.

An example of the transition of freeloading into closer relationships between species is the relationship between the sticky fish, which lives in tropical and subtropical seas, with sharks and cetaceans. The front dorsal fin of the sticker has been transformed into a suction cup, with the help of which it is firmly held on the surface of the body of a large fish. Biological meaning attachment of sticks is to facilitate their movement and settlement.

Representatives of different trophic levels are interconnected by one-way directed transfer of biomass into food chains. With each transition to the next trophic level, part of the available energy is not perceived, part is given off as heat, and part is spent on respiration. In this case, the total energy decreases several times each time. The consequence of this is the limited length of food chains. The shorter the food chain, or the closer the organism is to the beginning of it, the greater the amount of available energy in it.

Carnivore food chains go from producers to herbivores, which are eaten by small carnivores, which serve as food for larger carnivores, and so on. As they move up the predator chain, animals increase in size and decrease in number. The lengthening of the chain occurs due to the participation of predators in it. The relatively simple and short food chain of predators includes second-order consumers:

Grass (producer) -» Rabbits (consumer I order) ->

-» Fox (consumer II order).

A longer and more complex chain includes fifth-order consumers:

Pine -> Aphids -> Ladybugs -> Spiders ->

-» Insectivorous birds-> Birds of prey.

Grass -» Herbivorous mammals -> Fleas -> Flagellates.

In detrital chains, consumers are detritivores belonging to various systematic groups: small animals, mainly invertebrates, that live in the soil and feed on fallen leaves, or bacteria and fungi that decompose organic matter. In most cases, the activity of both groups of detritivores is characterized by strict coordination: animals create conditions for the work of microorganisms, dividing animal corpses and dead plants into small parts.

Detrital chains are distinguished from pasture chains also the fact that a large number of detritivorous animals form a kind of community, the members of which are connected with each other by various trophic connections (Fig. 10.4).

Rice. 10.4.

IN in this case we can talk about the existence of food webs of detritivores, separated from linear chains of predators. In addition, many detritivores are characterized by a wide range of nutrition and can, depending on the circumstances, use algae, small animals, etc., along with detritus.

Rice. 10.5. The most important connections in food webs: A - American prairie; b- ecosystems northern seas for herring

Food chains starting from green plants and from dead organic matter are most often present together in ecosystems, but almost always one of them dominates the other. However, in some specific environments (for example, abyssal and underground), where the existence of organisms with chlorophyll is impossible due to the lack of light, only detrital-type food chains are preserved.

Food chains are not isolated from one another, but are closely intertwined. They make up the so-called food webs. The principle of their formation is as follows. Each producer has not one, but several consumers. In turn, consumers, among whom polyphages predominate, use not one, but several food sources. To illustrate, we give examples of a relatively simple one (Fig. 10. 5a) and complex (Fig. 10.55) food webs.

In a complex natural community, those organisms that obtain food from plants occupying the first trophic level through the same number of stages are considered to belong to the same trophic level. Thus, herbivores occupy the second trophic level (the level of primary consumers), predators that eat herbivores occupy the third (the level of secondary consumers), and secondary predators occupy the fourth (the level of tertiary consumers). It must be emphasized that trophic classification divides into groups not the species themselves, but the types of their life activity. A population of one species can occupy one or more trophic levels, depending on what energy sources the species uses. Likewise, any trophic level is represented not by one, but by several species, resulting in food chains that are intricately intertwined.