One of the main concepts in modern ecology is the concept of an ecological niche. For the first time zoologists started talking about the ecological niche. In 1914 the American zoologist-naturalist J. Grinnell and in 1927 the English ecologist C. Elton defined the smallest unit of distribution of the species as the term “niche”, as well as the place of this organism in the biotic environment, its position in the food chains.

The generalized definition of an ecological niche is the following: it is the place of a species in nature, due to the cumulative set of environmental factors. The ecological niche includes not only the position of the species in space, but also its functional role in the community.

Is a set of environmental factors within which a particular type of organism lives, its place in nature, within which a given species can exist indefinitely.

Since a large number of factors should be taken into account when determining an ecological niche, the place of a species in nature described by these factors is a multidimensional space. This approach allowed the American ecologist G. Hutchinson to give the following definition of an ecological niche: it is a part of an imaginary multidimensional space, the individual dimensions of which (vectors) correspond to the factors necessary for the normal existence of the species. At the same time, Hutchinson singled out a niche fundamental, which a population can occupy in the absence of competition (it is determined by the physiological characteristics of organisms), and a niche implemented, those. part of the fundamental niche within which a species actually occurs in nature and which it occupies in the presence of competition with other species. It is clear that the realized niche, as a rule, is always less than the fundamental one.

Some ecologists emphasize that within their ecological niche, organisms must not only meet, but also be capable of reproduction. Since there is a species specificity to any ecological factor, the ecological niches of the species are also specific. Each species has its own characteristic ecological niche.

Most plant and animal species can exist only in special niches in which certain physicochemical factors, temperature and food sources are maintained. After the destruction of bamboo in China, for example, began, the panda, whose diet consists of 99% of this plant, was on the verge of extinction.

Species with common niches can easily adapt to changing habitat conditions, so the danger of their extinction is low. Typical representatives of species with common niches are mice, cockroaches, flies, rats and humans.

Gauze's law of competitive exclusion for ecologically close species in the light of the doctrine of the ecological niche can be formulated as follows: two species cannot occupy the same ecological niche. The way out of competition is achieved by the divergence of requirements for the environment, or, in other words, by delimiting the ecological niches of species.

Competing species that live together often “share” available resources to reduce competition. A typical example is the division into animals that are active during the day and are active at night. Bats (every fourth mammal in the world belongs to this suborder of bats) share the air space with other insect hunters - birds, using the change of day and night. True, bats have several relatively weak competitors, such as owls and nightjars, which are also active at night.

A similar division of ecological niches into day and night "shifts" is observed in plants. Some plants bloom during the day (most wild-growing species), others at night (lyubka two-leaved, fragrant tobacco). At the same time, nocturnal species also emit an odor that attracts pollinators.

The ecological amplitudes of some species are very small. So, in tropical Africa, one of the types of worms lives under the eyelids of a hippo and feeds exclusively on the tears of this animal. It is difficult to imagine a narrower ecological niche.

Ecological niche species concept

The position of the species that it occupies in the general system of biocenosis, including the complex of its biocenotic relationships and requirements for abiotic environmental factors, is called ecological niche of the species.

The concept of an ecological niche has proven to be very fruitful for understanding the laws of species living together. Ecological niche should be distinguished from habitat. In the latter case, it means that part of the space that is inhabited by the species and which has the necessary abiotic conditions for its existence.

The ecological niche of a species depends not only on the abiotic conditions of the environment, but also, at least, on its biocenotic environment. This is a characteristic of the way of life that a species can lead in a given community. There are as many species of living organisms on Earth - the same number of ecological niches.

Competitive exclusion rule can be expressed in such a way that the two species do not get along in the same ecological niche. The way out of competition is achieved due to the divergence of requirements for the environment, a change in lifestyle, which is the delineation of ecological niches of species. In this case, they acquire the ability to coexist in the same biocenosis.

Separation by cohabitating species of ecological niches with their partial overlapping - one of the mechanisms of stability of natural biocenoses. If any of the species sharply decreases its number or drops out of the community, others take on its role.

The ecological niches of plants, at first glance, are less diverse than those of animals. They are clearly delineated in species that differ in nutrition. In ontogeny, plants, like many animals, change their ecological niche. As they age, they use and transform the environment more intensively.

In plants, there is an overlap of ecological niches. It increases in certain periods when environmental resources are limited, but since species use resources individually, selectively and with different intensities, competition in stable phytocenoses is weakened.

The richness of ecological niches in the biocenosis is influenced by two groups of reasons. The first is the environmental conditions provided by the biotope. The more mosaic and more diverse the biotope, the more species can delimit their ecological niches in it.

Populations inhabiting common habitats inevitably enter into certain relationships in the field of nutrition, use of space, influence on the characteristics of the micro- and mesoclimate, etc. koinos - general), in which the selection of species is not random, but is determined by the possibility of continuous maintenance of the cycle of substances. Biocenosis is a form of organization of a living population, a multi-species ecosystem. It includes representatives of various taxa. K. Mobius was the first to note this in his book "Oysters and the oyster economy" (1877), introducing the term "biocenosis", and S. Forbes, in his work "Lake as a microcosm" (1887), approached the concept of an ecosystem. A clear doctrine of the ecosystem was formulated by the English ecologist A. Tensley (1935).

The main types of relationships between species in biocenoses are food (feeding of some species by others, competition for food), spatial (distribution in space, competition for a place of settlement or refuge) and habitat (formation of a biotope structure, microclimate).

Biocenosis - historically formed groups of the living population of the biosphere, inhabiting common habitats, arising on the basis of the biogenic cycle and providing it in specific natural conditions. All forms of biocenotic relations are carried out under certain conditions of the abiotic environment. The relief, climate, geological structure, hydrographic network, and other factors influence the composition and biological characteristics of the species that form the biocenosis, serve as a source of inorganic substances, and accumulate metabolic products. The inorganic environment - biotope - is a necessary part of the biocenotic system, a prerequisite for its existence. Academician V.N. Sukachev created the doctrine of biogeocenosis as a unity of biocenosis and its biotope. The biogeocenosis is spatially determined by the boundaries of the plant community (phytocenosis). A biogeocenosis is a set of homogeneous natural phenomena, which has its own specifics of the interaction of its constituent components and a certain type of exchange of matter and energy between themselves and other natural phenomena and is an internally contradictory unity that is in constant motion and development (V.N. Sukachev, 1964) ... Despite some differences, the terms “biocenosis”, “ecosystem” and “biogeocenosis” practically mean the same natural phenomenon - the supraspecific level of organization of biosystems.

Species structure of biocenoses

Each biocenosis is characterized by a specific species composition. Some species in it can be represented by a large population, while others are small. In this regard, one or several species can be distinguished that determine its appearance. As a rule, in the biocenosis, a small number of species have a large number and many species with a small number of individuals. So, in a forest consisting of dozens of plant species, only one or two of them give up to 90% of the timber. These species are called dominant, or dominant. They occupy a leading position in the biocenosis. Usually, terrestrial biocenoses are named according to the dominant species: larch forest, sphagnum bog, feather grass-fescue steppe.

Species that live off dominants are called predominants. For example, in the oak forest they include insects feeding on oak, jays, and murine rodents.

The species that create conditions for the life of other species of this biocenosis are called edificators. For example, in the taiga, spruce determines the nature of the formation of plant and animal communities, that is, the existence of a biocenosis is associated with it.

All species in the biocenosis are associated with dominant species and edificators. Within the biocenosis, groupings (complexes of populations) are formed, depending either on edificator plants or on other elements of the biocenosis.

The species structure of the biocenosis is characterized not only by the number of species in its composition (species diversity), but also by the ratio of their numbers. The quantitative ratio of species in the biocenosis is called the diversity index (H) and is usually determined by the Shannon formula: -Σ ρ i log 2 ρ i, where ρ i is the share of each species in the community.

Trophic structure of biocenoses

The main function of biocenoses - maintaining the cycle of substances in the biosphere - is based on the food relationships of species. Therefore, each biocenosis includes representatives of three ecological groups - producers, consumers and decomposers. In specific biocenoses, they are represented by populations of many species. Functionally, all types are divided into several groups depending on their place in the general system of the circulation of substances and the flow of energy. Species equivalent in this sense form the trophic level, and the relationships between species of different levels form a system of food chains. The totality of trophic chains in their specific expression forms the integral trophic structure of the biocenosis.

The group of producer species forms the level of primary production, at which external energy is utilized and a mass of organic matter is created. Primary producers are the basis of the trophic structure and the entire existence of the biocenosis. This level is made up of plants and photoautotrophic prokaryotes, chemosynthetic bacteria. The biomass of the substance synthesized by autotrophs is the primary production, and the rate of its formation is the biological productivity of the ecosystem. Productivity is expressed in terms of the amount of biomass synthesized per unit of time. The total amount of biomass is considered in this case as gross production, and that part of it, which determines the increase, as net production. The difference between gross and net production is determined by the expenditure of energy for vital activity ("the cost of breathing"), which can be, for example, in a temperate climate, up to 40-70% of gross production.

The pure primary production accumulated in the form of biomass of autotrophic organisms serves as a source of nutrition for representatives of the following trophic levels. Its consumers (consumers) form several (no more than 3-4) trophic levels.

I-st order consumables. This trophic level is compiled by the consumers of primary production. In the most typical cases, when it is created by photoautotrophs, these are herbivorous animals (phytophages). Species at this level are very diverse and adapted to feeding on plant food. Many phytophages have developed a gnawing type of mouth apparatus and adaptations for grinding food. Some animals are adapted to feeding on plant sap or flower nectar. Their oral apparatus is arranged in the form of a tube, with the help of which liquid food is absorbed. There are also adaptations to plant nutrition at the physiological level. In the body of most animals there are no cellulolytic enzymes, and the breakdown of fiber is carried out by symbiotic bacteria. Consumables partly use food to support life processes ("the cost of breathing"), and partly build their own body on its basis. This is the first stage in the transformation of organic matter synthesized by producers. The process of creating and accumulating biomass at the consumer level is called secondary production.

Order II consumables. This level unites animals with a carnivorous type of food (zoophages). This includes carnivores that feed on herbivorous animals and represent the 2nd stage of the transformation of organic matter in food chains. The chemicals that make up animal tissue are fairly uniform. Therefore, the transformation during the transition from one level of consumers to another is easier than the transformation of plant tissues into animals. Zoophages have adaptations to the nature of their diet. Their mouthpieces are adapted to grasp live prey. At the physiological level, the adaptations of zoophages are expressed primarily in the action of enzymes capable of digesting food of animal origin. Some predatory molluscs "drill" the shells of other molluscs using acids secreted by special glands.

The division of the biocenosis into trophic levels is only a general scheme. For example, there are species with a mixed diet. They can belong simultaneously to different trophic levels.

Ecological pyramid. The transition of biomass from one trophic level to another is associated with the loss of matter and energy. On average, it is believed that only about 10% of biomass and associated energy is transferred from level to level. Because of this, the total biomass, production and energy decrease as the trophic level rises. This pattern was noted by C. Elton in the form of the rule of ecological pyramids and acts as the main limiter of the length of food chains.

Each trophic level is composed of many species. An increase in the number of species in the biocenosis determines a more complete use of resources at each trophic level. This is due to an increase in the completeness of the biogenic circulation of substances. Species diversity acts as a mechanism that ensures the reliability of the circulation of substances. The essence of this mechanism is that monophagy - eating only one type of food - is rare in nature. Most animals consume a wide variety of food items. As a result, in addition to direct food links, side links arise that combine the flows of matter and energy of two or more food chains. In this way, food (trophic) webs are formed, in which the multiplicity of food chains acts as an adaptation to the sustainable existence of the ecosystem as a whole. Duplication of the flows of matter and energy along a multitude of parallel trophic chains maintains the continuity of the cycle in the event of disturbances in individual links of the food chain. Thus, the diversity of the species composition of the biocenosis acts as a mechanism for maintaining its stability.

Horizontal connections are also common in food webs. They unite animals of the same trophic level by the presence of common food items. This means the emergence of food competition between different species within the community. With strong food competition, some of the species were ousted from the composition of the community, or interspecific relationships were formed, weakening the force of competition. The amount of competition is determined by the number of foods common to competitors. Hence, the weakening of competition can go through the expansion of the food spectrum of competing species. An increase in the number of food items leads to a decrease in the relative volume of competition. The most effective way to get out of competition by reducing its volume is a high specialization in nutrition, leading to a divergence of food spectra.

The intensity of competition is determined by the ratio of the need for a given type of food for competing species and its abundance in nature. For example, near-water rodents (beaver, muskrat, water vole) feed on reeds and sedges. These plants are widespread in nature, have a high biomass and productivity. Therefore, the needs of all species of animals are met, and competition does not lead to negative consequences. In the event of a coincidence of limited food resources, the intensity of competition increases sharply and can cause the displacement of less competitive species from the community.

The ratio of volume and tension determines the overall strength of competition, which underlies the manifestation of various forms of relations between competing species. With a weakened force of competition, the system of horizontal ties is beneficial for the biocenosis. On its basis, the reliability of the functioning of ecosystems increases.

Decay chains. The processes considered above are associated with the synthesis and transformation of organic matter in food webs and characterize the so-called grazing chains, or grazing chains. The processes of destruction and mineralization of organic substances are usually displayed in a separate block - decomposition chains, or detrital chains. Their identification is due to the fact that organic mineralization occurs practically at all trophic levels. Plants and animals metabolize organic matter to carbon dioxide and water. Detrital chains begin with the decomposition of dead organic matter by saprophages. Saprophagous animals destroy dead organic matter, preparing it for the effects of decomposers. In terrestrial ecosystems, this process takes place in litter and soil. The most active part in the decomposition of dead organic matter is taken by soil invertebrates (worms and arthropods) and microorganisms. Large saprophages (eg insects) mechanically destroy dead tissue. They are not actually decomposers, but they prepare a substrate for organisms (bacteria and fungi) that carry out mineralization processes. Communities of saprophagous organisms are characterized by an unstable organization, some species are easily replaced by others.

Thus, at the consumer level, the flow of organic matter is divided into different groups of consumers. Living organic matter follows the chains of grazing, and the dead one follows the chains of decomposition. In terrestrial biocenoses, decomposition chains are of great importance in the biological cycle: they process up to 90% of the increase in plant biomass that enters these chains in the form of litter. In aquatic ecosystems, most of the matter and energy is included in the grazing chains.

Biocenosis as a living part of biogeocenosis

The set of co-living and mutually related organisms are called biocenoses (from the Latin bios - life, cenosis - general) (Figure 31).

microorganisms adapted to cohabitation in a given area.

The scale of biocenotic groupings of organisms is very different: from communities of lichen cushions on tree trunks or a decaying stump to the population of entire forests, steppes, and deserts.

There is no fundamental difference between biocenotic groupings of different scales. Smaller communities are a constituent, albeit relatively autonomous, part of larger ones, and these, in turn, are parts of communities on an even larger scale. So, the entire living population of lichen pads on the bark of a tree is part of a larger community of organisms associated with this tree and includes its subcrustal and trunk inhabitants, the crown population, etc. In turn, this grouping is only one of the constituent parts of the forest biocenosis. The latter is included in more complex complexes that ultimately form the entire living cover of the Earth. With an increase in the scale of communities, their complexity and the proportion of indirect, indirect connections between species increase.

The area of ​​the abiotic environment occupied by the biocenosis is called biotope (from Latin bios - life, topos - place).

The structure of any system is the patterns in the relationships and connections of its parts. The structure of the biocenosis is multifaceted, and when studying it, various aspects are distinguished.

1. Species structure of biocenosis ... The species structure of the biocenosis is understood as the diversity of species in it and the ratio of their number or mass. There are poor (for example, in the tundra, in the desert) and rich (for example, in tropical forests) species of biocenoses.

2. Spatial structure of biocenosis ... The spatial structure of the biocenosis is determined, first of all, by the addition of its plant part - phytocenosis, the distribution of ground and underground plant masses. When plants of different heights live together, the phytocenosis often acquires a clear tiered structure: the aboveground plant organs and their underground parts are located in several layers, using and changing the environment in different ways.

The position of the species that it occupies in the general system of biocenosis, the complex of its biocenotic connections and requirements for abiotic environmental factors are called ecological niche species.

Each organism lives surrounded by many others, enters into a wide variety of relationships with them both with negative and positive consequences for itself, and ultimately cannot exist without this living environment. Communication with other organisms is a necessary condition for nutrition and reproduction, the possibility of protection, mitigation of unfavorable environmental conditions, and on the other hand, it is a danger of damage and often even an immediate threat to the existence of an individual. The whole amount of influences that living beings have on each other are united by the name biotic factors of the environment.

The immediate living environment of the organism constitutes it biocenotic environment. Representatives of each species are able to exist only in such a living environment, where connections with other species provide them with normal living conditions. In other words, diverse living organisms are found on Earth not in any combination, but form certain cohabitations, or communities, which include species adapted to cohabitation.

Groupings of co-living and mutually related species are called biocenoses (from Latin "bios" - life, "cenosis" - general). The adaptability of members of the biocenosis to living together is expressed in a certain similarity of requirements for the most important abiotic environmental conditions and natural relationships with each other.

The concept of "biocenosis" is one of the most important in ecology. This term was proposed in 1877 by the German hydrobiologist K. Möbius, who studied the habitats of oysters in the North Sea. He found that oysters can live only under certain conditions (depth, currents, the nature of the soil, water temperature, salinity, etc.) and that a certain set of other species constantly lives with them - molluscs, fish, crustaceans, echinoderms, worms , coelenterates, sponges, etc. (Fig. 75). They are all interconnected and subject to environmental influences. Mobius drew attention to the pattern of such cohabitation. “Science, however, does not have a word by which such a community of living beings could be designated,” he wrote. - There is no word to denote a community in which the sum of species and individuals, constantly limited and subject to selection under the influence of external conditions of life due to reproduction, continuously owns a certain territory. I propose the term "biocenosis" for such a community. Any change in any of the factors of the biocenosis causes changes in other factors of the latter ”.

According to Möbius, the possibility of species to coexist for a long time with each other in the same biocenosis is the result of natural selection and has developed in the historical development of species. Further study of the patterns of composition and development of biocenoses led to the emergence of a special section of general ecology - biocenology.

The scale of biocenotic groupings of organisms is very different, from communities of lichen cushions on tree trunks or a decaying stump to the population of entire landscapes: forests, steppes, deserts, etc.

Rice. 75. Biocenoses of the Black Sea (after S. A. Zernov, 1949):

A - biocenosis of rocks: 1 - Pachygrapsis crab; 2 - barnacles Balanus; 3 – the Patella clam; 4–5 - seaweed; 6 - mussels; 7 - sea anemones; 8 - sea ruff;

B - sand biocenosis: 9 - nemeretina; 10 - Saccocirrus worms; 11 - amphipods; 12 - molluscs Venus; 13 - sultan fish; 14 - flounder; 15 - hermit crabs;

B - biocenosis of Zostera thickets: 16 - zostera; 17 - marine needles; 18 - greenfinches; 19 - Sea Horses; 20 - shrimps;

D - oyster biocenosis: 21 - oysters; 22 - scallops;

D - biocenosis of mussel ooze: 23 - mussels; 24 - red algae; 25 – red sponge Suberites; 26 - ascidian Ciona;

E - biocenosis of phaseolin sludge: 27 - phaseolin mollusc; 28 - echinoderm amphura; 29 - mollusk Trophonopsis;

F - hydrogen sulfide kingdom of bacteria;

З - biocenosis of open sea plankton: 31 - jellyfish, etc.

The term "biocenosis" in modern ecological literature is more often used in relation to the population of territorial areas, which on land are distinguished according to relatively homogeneous vegetation (usually along the boundaries of plant associations), for example, a spruce-sorrel biocenosis, a dry meadow biocenosis, a white-moss pine forest, a feather grass steppe biocenosis, wheat field, etc. This refers to the entire totality of living beings - plants, animals, microorganisms, adapted to cohabitation in a given territory. In the aquatic environment, biocenoses are distinguished that correspond to the ecological subdivisions of parts of water bodies, for example, biocenoses of coastal pebble, sandy or silty soils, abyssal depths, pelagic biocenoses of large water cycles, etc.

In relation to smaller communities (the population of trunks or foliage of trees, moss bumps in swamps, burrows, anthills, decaying stumps, etc.), various terms are used: "microcommunities", "biocenotic groupings", "biocenotic complexes", etc.

There is no fundamental difference between biocenotic groupings of different scales. Smaller communities are a constituent, albeit relatively autonomous, part of larger ones, and these, in turn, are parts of communities of an even larger scale. So, the entire living population of moss and lichen pillows on a tree trunk is part of a larger community of organisms associated with this tree and includes its subcrustal and trunk inhabitants, the population of the crown, rhizosphere, etc. In turn, this group is only one from the constituent parts of the forest biocenosis. The latter is included in more complex complexes that ultimately form the entire living cover of the Earth. Thus, the organization of life at the biocenotic level is hierarchical. With an increase in the scale of communities, their complexity and the proportion of indirect, indirect connections between species increase.

Natural associations of living beings have their own laws of addition, functioning and development, that is, they are natural systems.

Discussing the general principles of the organization of life on Earth, the well-known Russian biologist VN Beklemishev wrote: “All biocenotic stages of organization, from oceanic and epicontinental complexes to some microscopic lichens on the trunk of a pine tree, are very little individualized, little integrated, poorly organized, poorly closed. These are vague, not very definite, often hardly perceptible collective formations, intricately intertwined, imperceptibly passing into each other and nevertheless quite real, existing and acting, which we need to understand in all their complexity and vagueness, which is the task of biocenology with all its branches. "

Thus, being, like organisms, structural units of living nature, biocenoses nevertheless take shape and maintain their stability on the basis of other principles. They are systems of the so-called frame type, without special control and coordinating centers (such as the nervous or humoral systems of organisms), but they are also built on numerous and complex internal connections, have a regular structure and certain boundaries of stability.

According to the classification of the German ecologist W. Tischler, the most important features of the systems related to the supraorganic level of organization of life are the following:

1. Communities always arise, are made up of ready-made parts (representatives of various species or whole complexes of species) available in the environment. In this way, the way of their occurrence differs from the formation of a separate organism, an individual, which occurs through the gradual differentiation of primordia.

2. Parts of the community are replaceable. One species (or a complex of species) can take the place of another with similar ecological requirements without prejudice to the entire system. Parts (organs) of any organism are unique.

3. If the whole organism maintains constant coordination, consistency of the activity of its organs, cells and tissues, then the supraorganismic system exists mainly due to the balancing of oppositely directed forces. The interests of many species in biocenosis are directly opposite. For example, predators are antagonists of their prey, but nevertheless they exist together, within a single community.

4. Communities are based on the quantitative regulation of the number of some species by others.

5. The limiting dimensions of an organism are limited by its internal hereditary program. The sizes of the superorganic systems are determined by external factors. Thus, the biocenosis of a white moss pine forest can occupy a small area among bogs, or it can extend over a considerable distance in an area with relatively uniform abiotic conditions.

These special principles of the composition of supraorganic systems have caused a long discussion of ecologists, and primarily geobotanists, about the “continuity” and “discreteness” of the vegetation cover, which is the basis of terrestrial biocenoses (“continuum” is continuous, continuous, “discrete” is discontinuous). Proponents of the concept of the continuum focus on the gradual transitions from one phytocenosis to another, the absence of clear boundaries between them. From their point of view, phytocenosis is a rather conventional concept. In the organization of the plant community, the decisive role is played by environmental factors and the ecological individuality of species, which does not allow them to be grouped into clear spatial associations. Within the phytocenosis, each species behaves relatively independently. From the standpoint of continuity, species meet together not because they have adapted to each other, but because they have adapted to the common environment. Any variation in habitat conditions causes changes in the composition of the community.

The earlier concept of the discreteness of phytocenoses, which was put forward by S.G.Korzhinsky at the beginning of the formation of phytocenology, asserted the relationships of plants, i.e., internal factors, as the main ones in the organization of the plant community. Its modern supporters, recognizing the presence of transitions between phytocenoses, believe that plant communities exist objectively, and are not a conditional separation from a continuous vegetation cover. They pay attention to the frequency of occurrence of the same combinations of species under similar conditions, the important environmental-forming role of the most significant members of the phytocenosis, which affect the presence and distribution of other plants.

From the standpoint of the modern systemic approach to the organization of living nature, it becomes obvious that both previously irreconcilable points of view, as was often the case in the history of science, contain rational elements. Continuity, as a fundamental property of supraorganic systems, is complemented by the important role of internal connections in their organization, which, however, manifest themselves in a different form than in organisms.

7.2. Biocenosis structure

The structure of any system is the pattern in the relationship and connections of its parts. The structure of the biocenosis is multifaceted, and when studying it, various aspects are distinguished.

7.2.1. Species structure of biocenosis

Distinguish between the concepts of "species richness" and "species diversity" of biocenoses. Species richness Is a general set of community species, which is expressed by lists of representatives of different groups of organisms. Species diversity Is an indicator that reflects not only the qualitative composition of the biocenosis, but also the quantitative relationships of species.

Distinguish between poor and species-rich biocenoses. In polar arctic deserts and northern tundras with extreme heat deficiency, in waterless hot deserts, in reservoirs heavily polluted by wastewater - wherever one or several environmental factors deviate far from the average optimal level for life, communities are greatly depleted, since few species can adapt to such extreme conditions. The species spectrum is also small in those biocenoses that are often subjected to any catastrophic impacts, for example, annual flooding due to river floods or regular destruction of vegetation during plowing, the use of herbicides and other anthropogenic interventions. Conversely, wherever the conditions of the abiotic environment approach the optimal average for life, communities are extremely rich in species. Examples are rainforests, coral reefs with their diverse populations, river valleys in arid regions, etc.

The species composition of biocenoses, in addition, depends on the duration of their existence, the history of each biocenosis. Young, just emerging communities usually include a smaller set of species than long-established, mature ones. Biocenoses created by man (fields, orchards, vegetable gardens) are also poorer in species than natural systems similar to them (forest, steppe, meadow). Man maintains the monotony and species poverty of agrocenoses with a special complex system of agrotechnical measures - just remember the fight against weeds and plant pests.

However, even the most impoverished biocenoses include at least hundreds of species of organisms belonging to different systematic and ecological groups. In addition to wheat, the agrocenosis of a wheat field includes, at least in minimal quantities, a variety of weeds, wheat pests and predators feeding on phytophages, murine rodents, invertebrates - inhabitants of the soil and the ground layer, microscopic organisms of the rhizosphere, pathogenic fungi and many others.

Almost all terrestrial and most aquatic biocenoses include microorganisms, plants and animals. However, in some conditions, biocenoses are formed in which there are no plants (for example, in caves or reservoirs below the photic zone), and in exceptional cases, consisting only of microorganisms (for example, in an anaerobic environment at the bottom of reservoirs, in rotting silts, hydrogen sulfide springs, etc. . NS.).

It is rather difficult to calculate the total number of species in the biocenosis because of the methodological difficulties in accounting for microscopic organisms and the undeveloped taxonomy of many groups. It is clear, however, that species-rich natural communities include thousands and even tens of thousands of species, united by a complex system of various interrelationships.

The complexity of the species composition of communities largely depends on the heterogeneity of the habitat. In such habitats, where species of different ecological requirements can find conditions for themselves, communities richer in flora and fauna are formed. The influence of a variety of conditions on the diversity of species is manifested, for example, in the so-called borderline, or marginal, effect. It is well known that the forest edges are usually lush and richer vegetation, more species of birds nest, and more species of insects, spiders, etc., than in the depths of the forest. The conditions of illumination, humidity, temperature are more varied here. The stronger the differences between two adjacent biotopes, the more heterogeneous the conditions at their borders and the stronger the border effect is. The species richness increases strongly in the places of contact between forest and herbaceous, aquatic and terrestrial communities, etc. The manifestation of the boundary effect is characteristic of the flora and fauna of intermediate zones between contrasting natural zones (forest-tundra, forest-steppe). VV Alekhin (1882–1946) figuratively called the exceptional species richness of the flora of the European forest-steppe “Kursk floristic anomaly”.

In addition to the number of species that make up the biocenosis, in order to characterize its species structure, it is important to determine their quantitative ratio. If we compare, for example, two hypothetical groups, including 100 individuals of five identical species, from a biocenotic point of view, they may turn out to be unequal. A grouping in which 96 out of 100 individuals belong to one species and one individual to four others looks much more monotonous than one in which all 5 species are represented the same - 20 individuals each.

Number of a particular group of organisms in biocenoses strongly depends on their size. The smaller the individuals of the species, the higher their number in biotopes. So, for example, in soils the abundance of protozoa is calculated in many tens of billions per square meter, nematodes - several million, ticks and collembolans - tens or hundreds of thousands, earthworms - tens or hundreds of individuals. The number of burrowing vertebrates - murine rodents, moles, shrews - is no longer calculated per square meter, but per hectare of area.

Dimension species that make up natural biocenoses differ on a gigantic scale. For example, whales outnumber bacteria 5 million times in length and 3 × 10 20 in volume. Even within individual taxonomic groups, such differences are very large: if we compare, for example, giant trees and small grasses in the forest, tiny shrews and large mammals - elk, brown bear, etc. time. For example, the life cycles of unicellular organisms can occur within an hour, and the life cycles of large plants and animals are stretched over tens of years. The living space of an insect such as a gall midge can be limited by a closed gall on one leaf of a plant, while larger insects - bees collect nectar within a radius of a kilometer or more. Reindeer regularly migrate within hundreds or even more than a thousand kilometers. Some migratory birds live in both hemispheres of the Earth, covering tens of thousands of kilometers annually. On the one hand, natural biocenoses represent the coexistence of different dimensional worlds, and on the other hand, the closest connections are realized in them precisely among organisms of different sizes.

Naturally, in all biocenoses, the smallest forms, bacteria and other microorganisms, prevail numerically. Therefore, when comparing species of different sizes, the indicator of dominance in abundance cannot reflect the characteristics of the community. It is calculated not for the community as a whole, but for individual groupings, within which the difference in the sizes of individual forms can be neglected. Such groups can be distinguished according to different characteristics: systematic (birds, insects, grasses, Compositae), ecological and morphological (trees, grasses) or directly by size (microfauna, mesofauna and macrofauna of soils, microorganisms in general, etc.). Comparing the general characteristics of diversity, the quantitative ratios of the most abundant species within different size groups, the abundance of rare forms and other indicators, one can get a satisfactory idea of ​​the specificity of the species structure of the compared biocenoses.

Species of the same size class that are part of the same biocenosis differ greatly in abundance (Fig. 76). Some of them are rare, others so often that they determine the appearance of the biocenosis, for example, feather grass in the feather grass steppe or oxalis in the oxalis spruce forest. In each community, it is possible to distinguish a group of basic species, the most numerous in each size class, the connections between which, in fact, are decisive for the functioning of the biocenosis as a whole.

The dominant species are dominants community. For example, in our spruce forests, spruce dominates among trees, in the grass cover - oxalis and other species, in the bird population - kinglet, robin, chiffchaff, among murine rodents - red and red-gray voles, etc.

Dominants dominate the community and constitute the “species core” of any biocenosis (Fig. 77). Dominant, or massive, species determine its appearance, maintain the main connections, and influence the habitat to the greatest extent. Typically, typical terrestrial biocenoses are named after the dominant plant species: blueberry pine forest, hairy sedge birch forest, etc. In each of them, certain species of animals, fungi and microorganisms also dominate.

Rice. 76. The relationship between the number of species in a community and the number of individuals per species (according to Yu. Odum, 1975): 1, 2 - different types of communities

Rice. 77. The species structure of the collembola community for 5 years (according to N.A. Kuznetsova, A. B. Babenko, 1985).

The total species richness is 72 species. Dominants: 1 - Isotoma notabilis; 2 - Folsomia fimetarioides; 3 - Sphaeridia pumilis; 4 - Isotomiella minor; 5 - Friesea mirabilis; 6 - Onychiurus absoloni; 7 - other types

However, not all dominant species have the same effect on the biocenosis. Among them, there are those that, by their vital activity, to the greatest extent create an environment for the entire community, and without which, therefore, the existence of most other species is impossible. Such species are called edifiers (literal translation from Latin - builders) (Fig. 78). Removal of the edificator species from the biocenosis usually causes a change in the physical environment, primarily the microclimate of the biotope.

Rice. 78. Madrepore corals are the main edificators of coral reefs, determining the living conditions for thousands of species of aquatic organisms

The main edificators of terrestrial biocenoses are certain types of plants: in spruce forests - spruce, in pine forests - pine, in the steppes - turf grasses (feather grass, fescue, etc.). However, in some cases, animals can also be edificators. For example, in territories occupied by marmot colonies, it is their burrowing activity that mainly determines the nature of the landscape, and the microclimate, and the conditions for the growth of plants. In the seas, the typical edificators among animals are reef-forming coral polyps.

In addition to a relatively small number of dominant species, the biocenosis usually includes many small and even rare forms. The most common distribution of species by their abundance is characterized by the Raunkier curve (Fig. 79). A sharp rise in the left side of the curve indicates the predominance of small and rare species in the community, while a slight rise in the right side indicates the presence of a certain group of dominants, a “species core” of the community.

Rice. 79. The ratio of the number of species with different occurrence in biocenoses and the Raunkier curve (after P. Greig-Smith, 1967)

Rare and scarce species are also very important for the life of the biocenosis. They create its species richness, increase the diversity of biocenotic relationships and serve as a reserve for the replenishment and replacement of dominants, i.e., they give stability to the biocenosis and ensure the reliability of its functioning in different conditions. The larger the reserve of such "minor" species in the community, the more likely it is that among them there will be those that will be able to play the role of dominants under any changes in the environment.

There is a definite relationship between the number of dominant species and the general species richness of the community. With a decrease in the number of species, the abundance of individual forms usually increases sharply. In such impoverished communities, biocenotic connections are weakened and some of the most competitive species are able to reproduce without hindrance.

The more specific the environmental conditions, the poorer the species composition of the community and the higher the number of individual species can be. This pattern was named rules of A. Tinemann, named after a German scientist who studied the peculiarities of the species structure of communities in the 30s of the last century. In species-poor biocenoses, the number of individual species can be extremely high. Suffice it to recall outbreaks of mass reproduction of lemmings in the tundra or insect pests in agrocenoses (Fig. 80). A similar pattern can be traced in communities of all sizes. In piles of fresh horse manure, for example, an almost anaerobic environment, a lot of ammonia and other toxic gases, a high temperature due to the activity of microorganisms, that is, sharply specific living conditions deviating from the usual norm are created for various animals. In such heaps, the species composition of invertebrates is initially extremely poor. Drosophila fly larvae develop, and few species of saprophagous nematodes (family Rhabditidae) and carnivorous gamasid mites (genus Parasitus) breed. But on the other hand, all these species are extremely numerous, there are almost no rare forms. In such cases, the curve describing the distribution of species by their abundance has a strongly smoothed left side (as in Fig. 76). Such communities are unstable and are characterized by sharp fluctuations in the abundance of individual species.

Rice. 80. The structure of dominance in the insect community of the stalk of cereals in the fields (according to N.I.Kulikov, 1988). The abscissa shows species in descending order of abundance

Gradually, as manure decomposes and environmental conditions soften, the species diversity of invertebrates increases, while the relative and absolute numbers of mass forms noticeably decrease.

In the richest biocenoses, almost all species are few in number. In tropical forests, it is rare to find several trees of the same species nearby. In such communities, outbreaks of mass reproduction of certain species do not occur; biocenoses are highly stable. A curve reflecting a species structure of this type would have in Fig. 76 is a particularly steep left side.

Thus, even the most general analysis of the species structure can give quite a lot for the integral characterization of the community. The diversity of the biocenosis is closely related to its sustainability. Human activities greatly reduce the diversity in natural communities. This raises the need to anticipate its consequences and take measures to maintain natural systems.

Quantitative characteristics of the species in the biocenosis. To assess the role of a particular species in the species structure of the biocenosis, different indicators based on quantitative accounting are used. Abundance of species Is the number of individuals of a given species per unit area or volume of occupied space, for example, the number of small crustaceans in 1 dm 3 of water in a reservoir or the number of birds nesting per 1 km 2 of a steppe area, etc. Sometimes, to calculate the abundance of a species, instead of the number of individuals use the value of their total mass. For plants, the projective abundance, or area coverage, is also taken into account. Frequency of occurrence characterizes the uniformity or uneven distribution of the species in the biocenosis. It is calculated as the percentage of the number of samples or counting sites where the species occurs to the total number of such samples or sites. The abundance and occurrence of the species are not directly related. The species can be numerous, but with a low occurrence, or scanty, but quite common. Dominance degree - an indicator reflecting the ratio of the number of individuals of a given species to the total number of all individuals of the considered group. So, for example, if out of 200 birds registered in a given territory, 80 are finches, the degree of dominance of this species among the bird population is 40%.

To assess the quantitative ratio of species in biocenoses, modern ecological literature often uses diversity index, calculated by Shannon's formula:

H = – ?P i log 2 P i,

where? - the sign of the sum, p i Is the share of each species in the community (by number or mass), a log 2 p i- binary logarithm p i.

7.2.2. Spatial structure of biocenosis

The area of ​​the abiotic environment occupied by the biocenosis is called biotope, i.e., otherwise, bitop is the habitat of the biocenosis (from lat. bios- life, topos- a place).

The spatial structure of the terrestrial biocenosis is determined primarily by the addition of its plant part - phytocenosis, the distribution of the terrestrial and underground plant masses.

When plants of different heights live together, the phytocenosis often acquires a clear tiered folding: assimilating aboveground plant organs and their underground parts are arranged in several layers, using and changing the environment in different ways. Layering is especially noticeable in temperate forests. For example, in spruce forests, arboreal, grass-shrub and moss layers are clearly distinguished. Five or six tiers can be distinguished in a broad-leaved forest: the first, or upper, tier is formed by trees of the first size (pedunculate oak, heart-shaped linden, plane maple, smooth elm, etc.); the second - trees of the second size (mountain ash, wild apple and pear, bird cherry, goat willow, etc.); the third layer is the undergrowth formed by shrubs (common hazel, buckthorn brittle, forest honeysuckle, European spindle tree, etc.); the fourth consists of tall grasses (wrestlers, spreading pine forest, forest chase, etc.); the fifth tier is composed of lower grasses (common runny, hairy sedge, perennial forested forest, etc.); in the sixth tier - the lowest grasses, such as the European clefthoof. The undergrowth of trees and shrubs can be of different ages and sizes and do not form special layers. The most multi-tiered rainforests are rainforests, the least - artificial forest plantations (Fig. 81, 82).

There is always and in the forests inter-tiered (out-of-tier) plants - these are algae and lichens on the trunks and branches of trees, higher spore and flowering epiphytes, vines, etc.

Rice. 81. The multi-tiered rainforest of the Central Amazon. Vegetation of the strip 20 m long and 5 m wide

Rice. 82. Single-storey planted spruce forest. Monocultures of different ages

Tiering allows plants to more fully use the light flux: under the canopy of tall plants, shade-tolerant ones, up to shade-loving ones, can exist, intercepting even weak sunlight.

Layering is also expressed in herbaceous communities (meadows, steppes, savannas), but not always clearly enough (Fig. 83). In addition, they usually have fewer tiers than forests. However, in forests, there are sometimes only two clearly defined tiers, for example, in a white-moss forest (arboreal, formed by pine, and ground - from lichens).

Rice. 83. Layering of vegetation of the meadow steppe (after V.V. Alekhin, A.A.Uranov, 1933)

The tiers are distinguished according to the bulk of the assimilating organs of plants, which have a great influence on the environment. The vegetation layers can be of different lengths: the tree layer, for example, is several meters thick, and the moss cover is only a few centimeters thick. Each tier participates in its own way in creating a phytoclimate and is adapted to a specific set of conditions. For example, in a spruce forest, plants of the herb-dwarf shrub layer (oxalis, double-leaved mine, bilberry, etc.) are in conditions of dim lighting, equal temperatures (lower during the day and higher at night), weak wind, high humidity and CO2 content. Thus, the arboreal and herbaceous-shrub layers are in different ecological conditions, which affects the functioning of plants and the life of animals living within these layers.

The underground layering of phytocenoses is associated with different rooting depths of the plants that make up their composition, with the placement of the active part of the root systems. In the forests, you can often observe several (up to six) underground levels.

Animals are also predominantly confined to one or another layer of vegetation. Some of them do not leave the corresponding tier at all. For example, the following groups are distinguished among insects: soil inhabitants - geobium, ground, surface layer - herpetobium, moss layer - briobium, grass stand - phyllobium, higher tiers - aerobic. Among the birds there are species that nest only on the ground (chickens, grouse, skates, buntings, etc.), others - in the shrub layer (songbirds, bullfinches, warblers) or in tree crowns (finches, kinglets, goldfinches, large predators, etc. .).

Exploded horizontally - mosaic - is characteristic of almost all phytocenoses, therefore, structural units are distinguished within them, which have received different names: microgroups, microcenoses, microphytocenoses, parcels, etc. These microgroups differ in species composition, the quantitative ratio of different species, closeness, productivity and other properties.

Mosaicity is due to a number of reasons: the heterogeneity of the microrelief, soils, the environment-forming influence of plants and their biological characteristics. It can arise as a result of the activity of animals (the formation of soil emissions and their subsequent overgrowth, the formation of anthills, trampling and grazing of grass by ungulates, etc.) or a person (selective felling, fireplaces, etc.), due to tree felling during hurricanes, etc. ...

AA Uranov substantiated the concept of "phytogenic field". This term denotes that part of the space, which is influenced by an individual plant, shading it, removing mineral salts, changing the temperature and moisture distribution, supplying litter and metabolic products, etc. the structure of phytocenoses.

Changes in the environment under the influence of the vital activity of individual plant species create the so-called phytogenic mosaicity. It is well expressed, for example, in mixed coniferous-deciduous forests (Fig. 84). Spruce is stronger than deciduous trees, shades the soil surface, retains more rain moisture and snow with its crowns, spruce litter decomposes more slowly, contributes to soil podzolization. As a result, nemoral grasses grow well in spruce-deciduous forests under broad-leaved species and aspen, and typical boreal species under spruce.

Due to the differences in the environment-forming activity of different plant species, individual areas in the spruce-broad-leaved forest differ in many physical conditions (illumination, the thickness of the snow cover, the amount of litter, etc.), therefore life in them goes on differently: the herbage, undergrowth, root systems of plants, small animals, etc.

Rice. 84. Phytogenic mosaic of the lipo-spruce forest (after N.V. Dylis, 1971). Plots: 1 - spruce-hairy-sedge; 2 - spruce-mossy; 3 - dense spruce undergrowth; 4 - spruce-linden; 5 - aspen undergrowth; 6 - aspen-runny; 7 - large fern in the window; 8 - spruce-shchitnikovy; 9 - horsetail in the window

Mosaicity, like tiering, is dynamic: there is a change of some microgroups by others, their growth or reduction in size.

7.2.3. Ecological structure of biocenosis

Different types of biocenoses are characterized by a certain ratio of ecological groups of organisms, which expresses ecological structure community. Biocenoses with a similar ecological structure can have a different species composition.

Species performing the same functions in similar biocenoses are called vicarious (i.e., replacing). The phenomenon of ecological vicariate is widespread in nature. For example, marten in the European and sable in the Asian taiga, bison in the prairies of North America, antelopes in the savannas of Africa, wild horses and kulans in the steppes of Asia play a similar role. The specific species for the biocenosis is to a certain extent a random phenomenon, since communities are formed from those species that are in the environment. But the ecological structure of biocenoses, developing in certain climatic and landscape conditions, is strictly natural. So, for example, in biocenoses of different natural zones, the ratio of phytophages and saprophages naturally changes. In steppe, semi-desert and desert regions, phytophagous animals prevail over saprophages, in forest communities of the temperate zone, on the contrary, saprophagy is more developed. The main type of food for animals in the depths of the ocean is predation, while in the illuminated, surface zone of the pelagic zone, there are many filter feeders that consume phytoplankton, or species with a mixed diet. The trophic structure of such communities is different.

The ecological structure of communities is also reflected by the ratio of such groups of organisms as hygrophytes, mesophytes and xerophytes among plants or hygrophils, mesophiles and xerophiles among animals, as well as the spectra of life forms. It is quite natural that in dry arid conditions, the vegetation is characterized by a predominance of sclerophytes and succulents, and in highly humid biotopes, hygrophytes and even hydrophytes are richer. The diversity and abundance of representatives of a particular ecological group characterize a biotope no less than accurate measurements of the physical and chemical parameters of the environment.

This approach to the assessment of biocenoses, which uses the general characteristics of its ecological, species and spatial structure, ecologists call macroscopic. This is a generalized large-scale characteristic of communities, which makes it possible to navigate the properties of the biocenosis when planning economic activities, to predict the consequences of anthropogenic influences, and to assess the stability of the system.

Microscopic approach- this is a deciphering of the connections of each individual species in the community, a detailed study of the finest details of its ecology. This task has not yet been completed in relation to the overwhelming majority of species due to the extraordinary diversity of living forms in nature and the laboriousness of studying their ecological characteristics.

7.3. The relationship of organisms in biocenoses

The basis for the emergence and existence of biocenoses is represented by the relations of organisms, their connections, in which they enter with each other, inhabiting the same biotope. These connections determine the basic living conditions of species in the community, the possibility of obtaining food and conquering new space.

Classifications of biocenotic relations can be built using different principles. One of the popular approaches is to assess the possible result of contact between two individuals. For each of them, the result is taken as positive, negative or neutral. Combinations of results for 2 out of 3 possible results in a formal scheme of 6 options, which is the basis of this classification.

Predators usually refers to animals that feed on other animals, which they capture and kill. Predators are characterized by special hunting behavior.

The extraction of a victim requires from them a significant expenditure of energy for searching, chasing, capturing, overcoming the resistance of the victims.

If the size of the prey is much smaller than the size of the animals that feed on them, the number of food items is high and they themselves are easily accessible - in this case, the activity of the carnivorous species turns into a search and simple collection of prey and is called gathering.

Gathering requires the expenditure of energy mainly to search, not to capture food. Such "gathering" is typical, for example, for a number of insectivorous birds - plovers, plovers, finches, skates, etc. However, between typical predation and typical gathering in carnivores, there are many intermediate ways of obtaining food. For example, a number of insectivorous birds are characterized by hunting behavior when catching insects (swifts, swallows). Shrikes, flycatchers lie in wait and then catch up with the prey as typical predators. On the other hand, the way of feeding carnivorous gatherers is very similar to picking up motionless food by herbivorous animals, for example, seed-eating birds or rodents (turtledove, rock dove, lentils, wood mouse, hamsters, etc.), which are also characterized by specialized search forms of behavior.

Gathering can include filtration feeding of aquatic animals, sedimentation, or sedimentation of water suspension, collection of food by silt-eaters or earthworms. The so-called plant predation is also adjacent to it. In many plants, with a lack of nitrogen in their nutrition, methods have been developed for capturing and fixing insects arriving at them and digesting proteins from their bodies with proteolytic enzymes (pemphigus, sundew, nepentes, Venus flytrap, etc.).

By the way of mastering food items, gathering approaches the typical pasture phytophages. The specificity of grazing consists in eating stationary food, which is in relative abundance, and you do not have to spend a lot of effort looking for it. From an ecological point of view, this method of feeding is characteristic both for a herd of ungulates in a meadow, and for leaf-gnawing caterpillars in the crown of a tree or larvae of ladybirds in aphid colonies.

With a passive method of defense, protective coloration, hard shells, spines, needles, instincts for concealing, using shelters inaccessible to predators, etc. develop. Some of these methods of defense are characteristic not only of sedentary or sedentary species, but also of animals actively fleeing from enemies.

The defensive adaptations of potential victims are very diverse, sometimes very complex and unexpected. For example, cuttlefish, fleeing from a pursuing predator, empty their ink sac. According to the hydrodynamic laws, the liquid thrown out of the bag by a fast-swimming animal does not spread out for some time, acquiring the shape of a streamlined body close in size to the cuttlefish itself. Deceived by the dark outline that appeared in front of his eyes, the predator “grabs” the ink liquid, the narcotic effect of which temporarily deprives him of the opportunity to navigate in the environment. The method of protection in puffer fish is peculiar. Their shortened body is covered with adjoining spines. A large bag extending from the stomach allows these fish to swell into a ball in case of danger, swallowing water; at the same time, their needles are straightened and make the animal practically invulnerable to a predator. An attempt by a large fish to grab a blowfish can end in death for it from a prickly ball stuck in its throat.

In turn, the difficulty of detecting and catching prey contributes to the selection of predators for the best development of the sense organs (vigilance, subtle hearing, flair, etc.), for a faster reaction to prey, endurance during pursuit, etc. Thus, ecological relationships between predators and prey guide the evolution of related species.

Predators usually have a wide range of food. The extraction of victims requires a lot of strength and energy. Specialization would make predators highly dependent on the number of a certain prey species. Therefore, most of the species leading a predatory lifestyle are able to switch from one prey to another, especially to the one that is more accessible and abundant in a given period. True, many predators have preferred types of prey, which they prey more often than others. This selectivity can be due to various reasons. First, the predator actively chooses the most nutritious food in terms of food. For example, diving ducks and whitefishes in northern reservoirs are chosen from among aquatic invertebrates mainly the larvae of chironomid mosquitoes (bloodworms), and their stomachs are sometimes filled with bloodworms, despite the presence of other food in the reservoir.

The nature of the food can also be determined by passive selectivity: the predator first of all eats such food for the prey of which it is most adapted. Thus, many passerines feed on all insects that live openly on the soil surface, on grass, leaves, etc., but do not eat soil invertebrates, for which special devices are needed. Finally, the third reason for the food selectivity of predators may be active switching to the most massive prey, the appearance of which stimulates hunting behavior. With a high number of lemmings, even peregrine falcons, whose main method of hunting is to catch birds in the air, begin to hunt lemmings, seizing them from the ground. The ability to switch from one type of prey to another is one of the necessary ecological adaptations in the life of predators.

7.3.2. Commensalism

Commensalism - this is a form of relationship between two species, when the activity of one of them delivers food or shelter to the other (to the commensal). In other words, commensalism is the unilateral use of one species by another without harming it. Commensalism, based on the consumption of food leftovers from the owners, is also called parasitism. Such, for example, is the relationship between lions and hyenas, picking up the remains of prey that have not been eaten by lions. The commensals of large sharks are the accompanying fish, adhered, etc. The attitude of parasailing is established even between insects and some plants. In the liquid of pitchers of insectivorous nepentes, dragonfly larvae live, protected from the digestive action of plant enzymes. They feed on insects that end up in trapping jars. Excreta consumers are also commensals of other kinds.

The use of shelters is especially developed either in buildings or in bodies of other types. Such commensalism is called lodging. Fieraster fish hide in the aquatic lungs of sea cucumbers, juveniles of other fish - under the umbrellas of jellyfish protected by stinging threads. Commensalism is the settlement of epiphytic plants on the bark of trees. In the nests of birds, holes of rodents, a huge number of arthropod species live, using the microclimate of shelters and finding food there due to decaying organic remains or other species of cohabitants. Many species are specialized in this way of life and do not occur outside their burrows at all. Permanent burrowing or nesting cohabitants received the name nidicolov.

Relationships such as commensalism are very important in nature, as they contribute to closer cohabitation of species, more complete development of the environment and the use of food resources.

Often, however, commensalism is transformed into other types of relationships. For example, in the nests of ants, among a large number of their cohabitants, there are species of rove beetles from the genera Lomechusa and Atemeles. Their eggs, larvae and pupae are kept together with juvenile ants, which take care of them, lick and transfer them to special chambers. The ants also feed adult beetles. However, beetles and their larvae eat the eggs and larvae of the hosts, without meeting any resistance from their side. On the sides of the chest and the first segments of the abdomen, these beetles have special outgrowths - trichomes, at the base of which droplets of secretion are secreted, extremely attractive to ants. The secret contains ethers, which have an intoxicating, narcotic effect on ants, similar to the effect of alcohol. Ants constantly lick Lomehus and Atemeles. As a result, their instincts are upset, coordination of movements is disturbed, and even some morphological changes appear. Working ants in families with many Lomehus are inactive and lethargic. Families become small and die as a result.

7.3.3. Mutualism

A typical symbiosis is represented by the relationship between termites and their intestinal cohabitants - the flagellate order Hypermastigina. These protozoa produce the enzyme b-glucosidase, which converts fiber into sugars. Termites do not have their own intestinal enzymes for digesting cellulose and without symbionts they die of hunger. Young termites emerging from eggs lick the anus of adults, infecting themselves with flagellates. Flagellates find in the intestines of termites a favorable microclimate, protection, food and conditions for reproduction. In a free-living state, they do not actually occur in nature.

Intestinal symbionts involved in the processing of coarse plant feed have been found in many animals: ruminants, rodents, grinder beetles, May beetle larvae, etc. Species that feed on the blood of higher animals (ticks, leeches, etc.), as a rule, have symbionts, helping to digest it.

In multicellular animals and plants, symbiosis with microorganisms is very widespread. Many species of trees are known to cohabit with mycorrhizal fungi, leguminous plants - with the nodule bacteria Rhizobium, fixing molecular nitrogen in the air. Nitrogen-fixing symbionts were found on the roots of about 200 species of other groups of angiosperms and gymnosperms. Symbiosis with microorganisms sometimes goes so far that colonies of symbiotic bacteria can be considered as specialized organs of multicellular organisms. Such, for example, are the mycetomas of cuttlefish and some squid - sacs filled with luminous bacteria and which are part of the organs of luminescence - photophores.

The line between symbiosis and other types of relationships is sometimes rather arbitrary. It is interesting to use their intestinal microflora by lagomorphs and some rodents. In rabbits, hares, pikas, regular eating of their own feces was found. Rabbits produce two types of excrement: dry and soft, mucous membranes. They lick soft feces directly from the anus and swallow without chewing. Studies have shown that this coprophagia is completely natural. Rabbits, deprived of the opportunity to consume soft feces, lose weight or gain poorly in weight and are more likely to be susceptible to various diseases. Soft feces of rabbits are almost unchanged contents of the cecum, enriched with vitamins (mainly B 12) and protein substances. The cecum of the lagomorphs is a fermentation vat for processing fiber and is saturated with symbiotic microorganisms. There are up to 10 billion bacteria in 1 g of soft feces. Getting along with feces into the stomach of a rabbit, microorganisms are completely killed under the influence of acid and are digested in the stomach and long small intestine. Thus, in exclusively herbivorous lagomorphs, coprophagia is a way of obtaining essential amino acids.

Less obligatory, but extremely essential is the mutualistic relationship between the Siberian cedar pine and the birds nesting in the cedar forests — the nutcracker, nuthatch, and kuksa. These birds, feeding on pine seeds, have instincts for storing food. They hide small portions of "nuts" under a layer of moss and forest litter. The birds do not find a significant part of the reserves, and the seeds germinate. The activity of these birds, thus, contributes to the self-renewal of cedar forests, since the seeds cannot germinate on a thick layer of forest litter, which blocks their access to the soil.

There is a mutually beneficial relationship between plants that have succulent fruits and birds that feed on these fruits and spread seeds that are usually indigestible. Mutualistic relations with ants develop in many plants: about 3000 species are known that have adaptations for attracting ants. A typical example is cecropia, a tree native to the Amazon. Ants of the genera Azteca and Cramatogaster colonize the voids in the articulate trunk of the cecropia and feed on special rounded formations about 1 mm in diameter - "Müllerian bodies", which the plant produces on the bulges located on the outer side of the leaf sheath. House ants vigilantly protect leaves from pests, especially from leaf-cutting ants of the genus Atta.

The more diverse and stronger the ties that support the cohabitation of species, the more stable their cohabitation. Communities with a long history of development are therefore more durable than those that arise after sudden disturbances in the natural environment or are created artificially (fields, orchards, vegetable gardens, greenhouses, greenhouses, aquariums, etc.).

7.3.4. Neutralism, amensalism

Neutralism - this is a form of biotic relations in which the cohabitation of two species on the same territory does not entail either positive or negative consequences for them. Under neutralism, the species are not directly related to each other, but depend on the state of the community as a whole. For example, squirrels and moose, living in the same forest, practically do not contact each other. However, the oppression of the forest by a prolonged drought or its exposure during mass reproduction of pests affects each of these species, although to a different extent. Relations of the type of neutralism are especially developed in species-rich communities, including members of different ecology.

At amensalism for one of the two interacting species, the consequences of living together are negative, while the other receives neither harm nor benefit from them. This form of interaction is more common in plants. For example, light-loving herbaceous species growing under a spruce are oppressed as a result of strong shading by its crown, while for the tree itself, their neighborhood may be indifferent.

Relationships of this type also lead to the regulation of the number of organisms, affect the distribution and mutual selection of species.

7.3.5. Competition

Competition - This is the relationship of species with similar ecological requirements existing at the expense of common resources that are in short supply. When such species live together, each of them is at a disadvantage, since the presence of the other reduces the possibilities for mastering food, shelter and other livelihoods that the habitat has. Competition is the only form of environmental relations that negatively affects both interacting partners.

The forms of competitive interaction can be very different: from direct physical struggle to peaceful coexistence. Nevertheless, if two species with the same ecological needs end up in the same community, sooner or later one competitor crowds out the other. This is one of the most general environmental rules, which is called competitive exclusion law and was formulated by GF Gause.

In a simplified form, it sounds like "two competing species do not get along together."

The incompatibility of competing species was emphasized even earlier by Charles Darwin, who considered competition to be one of the most important components of the struggle for existence, playing a large role in the evolution of species.

In the experiments of GF Gause with the cultures of the slippers of Paramecium aurelia and P. caudatum, each of the species, placed separately in test tubes with hay infusion, multiplied successfully, reaching a certain level of abundance. If both species with a similar feeding pattern were placed together, then at first there was an increase in the number of each of them, but then the number of P. caudatum gradually decreased and they disappeared from the infusion, while the number of P. aurelia remained constant (Fig. 86).

Rice. 86. Growth in the number of ciliates Paramaecium caudatum (1) and P. aurelia (2) (according to GF Gauze from F. Dre, 1976): A - in a mixed culture; B - in separate cultures

The winner in the competitive struggle is, as a rule, the species that, in a given ecological situation, has at least small advantages over another, that is, it is more adapted to environmental conditions, since even closely related species never coincide across the entire ecological spectrum. So, in the experiments of T. Parkas with laboratory cultures of flour beetles, it was revealed that the result of competition can be determined by the temperature and humidity at which the experiment proceeds. In numerous cups of flour, in which were placed several specimens of two species of beetles (Tribolium confusum and T. castaneum) and in which they multiplied, after a while only one of the species remained. At high temperature and humidity of flour it was T. castaneum, at lower temperature and moderate humidity it was T. confusum. However, with average values ​​of factors, the “victory” of one type or another was clearly random, and it was difficult to predict the outcome of competition.

The reasons for the displacement of one species by another may be different. Since the ecological spectra of even closely related species never coincide completely, despite the general similarity of requirements for the environment, the species still differ in some way from each other. Even if such species coexist peacefully together, but the intensity of reproduction of one is slightly more than the other, then the gradual disappearance of the second species from the community is only a matter of time, since with each generation more and more resources are captured by a more competitive partner. Often, however, competitors actively influence each other.

In plants, the suppression of competitors occurs as a result of the interception of mineral nutrients and soil moisture by the root system and sunlight - by the leaf apparatus, as well as as a result of the release of toxic compounds. For example, in mixed crops of two types of clover, Trifolium repens forms a leaf canopy earlier, but then it is shaded by T. fragiferum, which has longer petioles. With the joint cultivation of duckweeds Lemna gibba and Spirodela polyrrhiza, the number of the second species first increases and then decreases, although in pure crops the growth rate of this species is higher than that of the first. The advantages of L. gibba in this case are that in conditions of thickening, it develops aerenchyma, which helps to stay on the water surface. S. polyrrhiza, which lacks aerenchyma, is pushed down and shaded by a competitor.

The chemical interactions of plants through their metabolic products are called allelopathy. Similar ways of influencing each other are characteristic of animals. In the above experiments by GF Gause and T. Park, suppression of competitors occurred mainly as a result of the accumulation of toxic metabolic products in the environment, to which one of the species is more sensitive than the other. Higher plants with a low demand for nitrogen, the first to appear on fallow soils, suppress the formation of nodules in legumes and the activity of free-living nitrogen-fixing bacteria by root excretions. By preventing the enrichment of the soil with nitrogen, they gain an advantage in competition with plants that need a large amount of nitrogen in the soil. Cattail in overgrown water bodies is allelopathically active in relation to other aquatic plants, which allows it, avoiding competitors, to grow in almost clean thickets.

In animals, there may be cases of direct attack by one species on another in a competitive struggle. For example, the larvae of the egg-eaters Diachasoma tryoni and Opius humilis, trapped in the same host egg, fight each other and kill the rival before starting to feed.

The possibility of competitive displacement of one species by another is the result of ecological individuality of species. In unchanged conditions, they will have different competitiveness, since they necessarily differ from each other in tolerance to any factors. In nature, however, in most cases the environment is changeable both in space and in time, and this makes it possible for many competitors to coexist. For example, if weather conditions more or less regularly change in favor of one or another species, the beginning processes of displacing each other by them do not reach the end and change their sign to the opposite. So, in wet years, mosses can grow in the lower tier of the forest, and in dry years they are pressed by the cover of hairy sedges or other grasses. These species also coexist in one phytocenosis, occupying forest areas with different moisture conditions. In addition, species competing not for one, but for several resources often have different thresholds of limiting factors, which also prevents the completion of competitive exclusion processes. Thus, the American ecologist D. Tilman, cultivating two species of diatoms together, found that they do not displace each other, because they have different sensitivity to the lack of nitrogen and silicon. A species that is able to reproduce ahead of another at a low nitrogen content cannot achieve this due to a lack of silicon for it, while its competitor, on the contrary, has enough silicon, but little nitrogen.

Competing species can get along in the community even if the increase in the number of a stronger competitor is not allowed by the predator. In this case, the activity of the predator leads to an increase in the species diversity of the community. In one of the experiments from the bottom of the coastal area of ​​the sea, where 8 species of sessile invertebrates lived - mussels, sea acorns, sea ducks, chitons - a predator, a starfish, which feeds mainly on mussels, was removed. After a while, mussels occupied the entire area of ​​the bottom, displacing all other species.

Thus, biocenoses in each group of organisms contain a significant number of potential or partial competitors, which are in dynamic relations with each other. A species may not have strong rivals either, but it may be slightly influenced by each of the many others, partially using its resources. In this case, they talk about "Diffuse" competition, the outcome of which also depends on many circumstances and may end with the displacement of this species from the biocenosis.

Competition, therefore, has a double meaning in biocenoses. It is a factor that largely determines the species composition of communities, since intensely competing species do not get along together. On the other hand, partial or potential competition allows species to quickly capture additional resources that are released when the activities of neighbors are weakened and replace them in biocenotic connections, which preserves and stabilizes the biocenosis as a whole.

As with any form of biotic relationship, competition is often difficult to separate from other types of relationship. In this regard, the behavioral features of ecologically similar ant species are indicative.

Large meadow ants Formica pratensis build bulk nests and guard the area around them. In the smaller F. cunicularia, the nests are small, in the form of earthen mounds. They often settle on the periphery of the nesting territory of meadow ants and hunt in their foraging areas.

With the experimental isolation of meadow ant nests, the hunting efficiency of F. cunicularia increases 2–3 times. The ants produce larger insects, which are usually prey for F. pratensis. If F. cunicularia nests are isolated, the production of meadow ants does not increase, as one would expect, but is halved. It turned out that the more mobile and active foragers of F. cunicularia serve as stimulators of the search activity of meadow ants, a kind of scouts for protein food. The intensity of movement of foragers of meadow ant along the roads in those sectors where there are nests of F. cunicularia is 2 times higher than where they are not. Thus, the overlap of the hunting territory and food spectra allows us to consider F. cunicularia as a competitor to meadow ants, but the increase in the efficiency of F. pratensis hunting indicates the benefits of F. cunicularia stay on their territory.

Rice. 87. A female deep-sea anglerfish with three males attached to it

Mutualistic and competitive relationships are the main essence of intraspecific relationships. The study of the role of these relationships within the species, diversity and specificity of their forms is the subject of a special section of synecology - ecology of populations.

As can be seen from the above examples, the formal classification of the types of biotic connections cannot fully reflect all their diversity and complexity in living nature, but still allows one to navigate in the main types of interaction between organisms. Other classifications draw attention to other aspects of biotic relationships using different approaches.

VN Beklemishev subdivided relations between species in a community into direct and indirect. Direct connections arise from direct contact of organisms. Indirect links represent the influence of species on each other through the habitat or by affecting third species.

According to the classification of V.N. Beklemishev, direct and indirect interspecific relations, according to the value they may have in the biocenosis, are divided into four types: trophic, topical, phoric, and factory.

7.3.6. Trophic connections

Trophic connections arise when one species feeds on another - either living individuals, or their dead remains, or waste products. And dragonflies, catching other insects on the fly, and dung beetles, feeding on the droppings of large ungulates, and bees collecting plant nectar, enter into a direct trophic relationship with the species that provide them with food. In the case of competition between two species due to food objects, an indirect trophic relationship arises between them, since the activity of one is reflected in the supply of food to the other. Any effect of one species on the consumption of another or the availability of food for it should be regarded as an indirect trophic relationship between them. For example, caterpillars of nun moths, eating the needles of pine trees, facilitate access to weakened trees for bark beetles.

Trophic connections are the main ones in communities. It is they who unite the species living together, since each of them can live only where there are food resources it needs. Any species is not only adapted to certain food sources, but itself serves as a food resource for others. Nutritional relationships in nature create a food web that ultimately extends to all species in the biosphere. The image of this food web can be recreated by placing any species in the center and connecting it with arrows to all others that are in direct or indirect food relations with it (Fig. 88), and then continue this procedure for each species involved in the scheme. As a result, all wildlife will be covered, from whales to bacteria. As the studies of Academician A. M. Ugolev have shown, there is "an extraordinary uniformity of the properties of assimilation systems at the molecular and supramolecular levels in all organisms of the biosphere," which allows them to receive energy resources from each other. He argues that behind the endless variety of types of food there are common fundamental processes that form a single system of trophic interactions on a planetary scale.

Rice. 88. Herring food links are part of the ocean food web

Any biocenosis is permeated with food links and is a more or less localized in space section of a common food web that connects all life on Earth.

7.3.7. Topical connections

Individual consortia can be of varying degrees of complexity. The largest number of consortium connections are those plants that play the main role in creating the internal environment of the biocenosis. Since each member of a large consortium can, in turn, be the center of a smaller association, consortia of the first, second and even third order can be distinguished. Thus, a biocenosis is a system of interconnected consortia that arise on the basis of the closest topical and trophic relationships between species. Consort relationships, which are based on topical relationships, form a kind of block structure of the biocenosis.

Topical and trophic relationships are of the greatest importance in the biocenosis, they form the basis of its existence. It is these types of relationships that keep organisms of different species close to each other, uniting them into fairly stable communities of different scales.

7.3.8. Phoric connections

Phoric connections Is the participation of one species in the spread of another. Animals act as transporters. The transfer of seeds, spores, pollen by animals is called zoochory, transfer of other, smaller animals - phoresis (from lat. foras- out, out). The transfer is usually carried out with the help of special and various devices. Animals can capture plant seeds in two ways: passive and active. Passive seizure occurs when the body of an animal accidentally touches a plant, the seeds or seedlings of which have special hooks, hooks, outgrowths (string, burdock). They are usually distributed by mammals, which sometimes carry such fruits on wool over rather long distances. An active way of capturing is eating fruits and berries. Animals shed non-digestible seeds along with their droppings. Insects play an important role in the transfer of fungal spores. Apparently, the fruiting bodies of fungi arose as formations attracting settling insects.

Rice. 89. Phoresia of mites on insects:

1 - the deutonymph of the uropod mite is attached to the beetle with a stalk of hardened secretory fluid;

2 - phoresis of ticks on ants

Phoresia of animals is widespread mainly among small arthropods, especially among various groups of ticks (Fig. 89). It represents one of the methods of passive dispersal and is characteristic of species for which transfer from one biotope to another is vital for conservation or prosperity. For example, many flying insects - visitors to accumulations of rapidly decaying plant debris (animal corpses, ungulate droppings, heaps of decaying plants, etc.) carry gamasid, uropodic or tyroglyphoid mites, which migrate in this way from one accumulation of food materials to another. Their own resettlement opportunities do not allow these species to cover significant distances for them. Dung beetles sometimes crawl with raised elytra, which are unable to fold due to mites densely dotted with their bodies. Some types of nematodes spread to insects by means of phoresia (Fig. 90). The legs of dung flies often look like lamp brushes due to the abundance of nematodrabditids attached to them. Among large animals, phoresia is almost never found.

Rice. 90. Dissemination of nematode larvae on beetles:

1 - larvae waiting for the settler;

2 - larvae attached under the beetle's elytra

7.3.9. Factory connections

Factory connections - this is a type of biocenotic relationship that a species enters into, which uses excretion products for its structures (fabrications), or dead remains, or even living individuals of another species. For example, birds use tree branches, mammalian wool, grass, leaves, down and feathers of other bird species, etc. to build nests. Caddis larvae build houses from pieces of branches, bark or leaves of plants, from the shells of small types of coils, capturing even shells with live shellfish. The megahila bee places eggs and supplies in cups made from soft leaves of various shrubs (rose hips, lilacs, acacia, etc.).

Rice. 91. Scheme of the influence of pH on the growth of various plants when grown in single-species crops and under competitive conditions:

1 - curves of the physiological optimum;

2 - synecological optimum (according to V. Larher, 1978)

7.4. Ecological niche

The position of the species that it occupies in the general system of biocenosis, the complex of its biocenotic connections and requirements for abiotic environmental factors are called ecological niche species.

The concept of an ecological niche has proven to be very fruitful for understanding the laws of species living together. Many ecologists have worked on its development: J. Grinnell, C. Elton, G. Hutchinson, J. Odum, and others.

Ecological niche should be distinguished from habitat. In the latter case, it means that part of the space that is inhabited by the species and which has the necessary abiotic conditions for its existence. The ecological niche of a species depends not only on the abiotic conditions of the environment, but also, at least, on its biocenotic environment. The nature of the occupied ecological niche is determined both by the ecological possibilities of the species and by the extent to which these possibilities can be realized in specific biocenoses. This is a characteristic of the way of life that a species can lead in a given community.

G. Hutchinson put forward the concept of a fundamental and realized ecological niche. Under fundamental the whole set of conditions under which a species can successfully exist and reproduce is understood. In natural biocenoses, however, species do not master all the resources suitable for them due, first of all, to competitive relations. Realized ecological niche - This is the position of a species in a specific community, where it is limited by complex biocenotic relationships. In other words, the fundamental ecological niche characterizes the potential of the species, and the realized one - that part of them that can be realized under the given conditions, given the availability of the resource. Thus, the realized niche is always less than the fundamental one.

In ecology, the question of how many ecological niches a biocenosis can accommodate and how many species of a particular group with similar environmental requirements can coexist is widely discussed.

The specialization of a species in nutrition, use of space, time of activity and other conditions is characterized as a narrowing of its ecological niche, the reverse processes - as its expansion. The expansion or contraction of the ecological niche of a species in the community is greatly influenced by competitors. Competitive exclusion rule, formulated by GF Gause for ecologically close species, it can be expressed in such a way that two species do not get along in one ecological niche.

Experiments and observations in nature show that in all cases where species cannot avoid competition for basic resources, weaker competitors are gradually pushed out of the community. However, in biocenoses, there are many opportunities for at least partial delimitation of ecological niches of ecologically close species.

The way out of competition is achieved due to the divergence of requirements for the environment, a change in lifestyle, which, in other words, is the delineation of ecological niches of species. In this case, they acquire the ability to coexist in the same biocenosis. Each of the species living together in the absence of a competitor is capable of a more complete use of resources. This phenomenon is easy to observe in nature. So, herbaceous plants of the spruce forest are able to be content with a small amount of soil nitrogen, which remains from the interception of it by the roots of trees. However, if the roots of these spruces are chopped off in a limited area, the conditions for nitrogen nutrition of the grasses are improved and they grow vigorously, taking on a dense green color. Improvement of living conditions and an increase in the number of a species as a result of the removal from the biocenosis of another, close in ecological requirements, is called competitive release.

The division by co-living species of ecological niches with their partial overlap is one of the mechanisms of stability of natural biocenoses. If any of the species sharply decreases its number or drops out of the community, others take on its role. The more species in the biocenosis, the lower the number of each of them, the more pronounced their ecological specialization. In this case, one speaks of “denser packing of ecological niches in the biocenosis”.

In closely related species living together, very fine delineations of ecological niches are usually observed. So, ungulates grazing in the African savannas use pasture food in different ways: zebras mainly cut off the tops of grasses, wildebeests feed on what the zebras leave them, while choosing certain types of plants, gazelles pluck out the lowest grasses, and swamp antelopes are content with high dry stems left over from other herbivores. The same "division of labor" in the southern European steppes was once carried out by wild horses, marmots and ground squirrels (Fig. 92).

Rice. 92. Different types of herbivores eat grass at different heights in the African savannas (upper rows) and in the steppes of Eurasia (lower rows) (after F.R. Fuente, 1972; B.D. Abaturov, G.V. Kuznetsov, 1973)

In our winter forests, tree-feeding insectivorous birds also avoid competing with each other through different search patterns. For example, nuthatches and pikas collect food on trunks. At the same time, nuthatches rapidly examine the tree, quickly seizing insects or seeds that come across large cracks in the bark, while small pikas carefully rummage the slightest cracks on the surface of the trunk, into which their thin awl-shaped beak penetrates. In winter, in mixed flocks, great tits search extensively in trees, in bushes, on stumps, and often in the snow; titmouse-chicks mainly examine large branches; long-tailed tits seek food at the ends of branches; small beads carefully ransack the upper parts of the coniferous crowns.

Ants exist in natural conditions in multi-species associations, the members of which differ in their way of life. In the forests of the Moscow region, the following association of species is most often found: the dominant species (Formica rufa, F. aquilonia, or Lasius fuliginosus) occupies several layers, L. flavus is active in the soil, Myrmica rubra is active in the forest floor, L. niger and F. fusca, trees - Camponotus herculeanus. Specialization to life in different tiers is reflected in the life form of the species. In addition to separation in space, ants also differ in the nature of obtaining food, in the time of daily activity.

In deserts, the most developed complex of ants collecting food on the soil surface (herpetobionts). Among them, representatives of three trophic groups stand out: 1) daytime zooonecrophages are active in the hottest time, feed on the corpses of insects and small live insects that are active during the day; 2) nocturnal zoophages - they hunt sedentary insects with soft covers that appear on the surface only at night, and molting arthropods; 3) carpophages (day and night) - they eat plant seeds.

Several species from one trophic group can live together. The mechanisms for getting out of competition and delimiting ecological niches are as follows.

1. Dimensional differentiation (fig. 93). For example, the average weights of workers of the three most common daytime zooonecrophages in the sands of the Kyzyl Kum desert are 1: 8: 120. Approximately the same ratio of weights in a medium-sized cat, lynx and tiger.

Rice. 93. Comparative sizes of four species of ants from the group of diurnal zooonecrophages in the sandy desert of the Central Karakum desert and distribution of prey of three species by weight classes (according to G.M. Dlussky, 1981): 1 - medium and large workers Cataglyphis setipes; 2 - C. pallida; 3 - Acantholepis semenovi; 4 - Plagiolepis pallescens

2. Behavioral differences consist in different foraging strategies. The ants that create roads and use the mobilization of porters to transport discovered food to the nest feed mainly on the seeds of the clumping plants. Ants, whose foragers work as solitary collectors, collect mainly seeds from dispersed plants.

3. Spatial differentiation. Within the same tier, food collection by different species can be confined to different areas, for example, in open places or under wormwood bushes, on sandy or clayey areas, etc.

4. Differences in activity times refer mainly to the time of day, but in some species mismatches in activity and seasons of the year (mainly spring or autumn activity) were noted.

Ecological niches of species are variable in space and time. They can be sharply differentiated in individual development, depending on the stage of ontogenesis, as, for example, in caterpillars and adults of lepidoptera, larvae and beetles of May beetle, tadpoles and adult frogs. In this case, both the habitat and the entire biocenotic environment change. In other species, the ecological niches occupied by young and adult forms are closer, but nevertheless there are always differences between them. Thus, adult perches and their fry living in the same lake use different energy sources for their existence and enter different food chains. Fry live off small plankton, while adults are typical predators.

The weakening of interspecific competition leads to the expansion of the ecological niche of the species. On oceanic islands with poor fauna, a number of birds, in comparison with their relatives on the mainland, inhabit more diverse habitats and expand the range of food, since they do not collide with competing species. In island inhabitants, there is even an increased variability in the shape of the beak as an indicator of the expansion of the nature of food connections.

If interspecific competition narrows the ecological niche of a species, preventing all its potencies from manifesting itself, then intraspecific competition, on the contrary, promotes the expansion of ecological niches. With the increased number of the species, the use of additional forages begins, the development of new habitats, the emergence of new biocenotic relationships.

In water bodies, plants completely immersed in water (elodea, hornwort, urut) find themselves in different conditions of temperature, illumination, gas regime than those floating on the surface (telores, vodokras, duckweed) or rooting at the bottom and carrying leaves to the surface (water lily, egg-capsule, victoria). They also differ in their relationships with the environment. Epiphytes of tropical forests occupy similar, but still not identical niches, since they belong to different ecological groups in relation to light and water (heliophytes and sciophytes, hygrophytes, mesophytes and xerophytes). Various epiphytic orchids have highly specialized pollinators.

In a mature broad-leaved forest, trees of the first tier - common oak, smooth elm, plane maple, heart-leaved linden, common ash - have similar life forms. The tree canopy formed by their crowns turns out to be in the same horizon, under similar environmental conditions. But close analysis shows that they participate in the life of the community in different ways and, therefore, occupy different ecological niches. These trees differ in the degree of light love and shade tolerance, the timing of flowering and fruiting, the methods of pollination and distribution of fruits, the composition of consorts, etc. Oak, elm and ash are anemophilic plants, but the saturation of the environment with their pollen occurs at different times. Maple and linden are entomophiles, good honey plants, but bloom at different times. The oak has a zoochoria, the rest of the broad-leaved trees have an anemochoria. The composition of the consorts is different for everyone.

If in a broad-leaved forest the crowns of trees are in the same horizon, then the active root ends are located at different depths. The roots of the oak penetrate the deepest, the roots of the maple are located higher, and even more superficially - the ash. The litter of different types of trees is utilized at different rates. Linden, maple, elm, ash leaves almost completely decompose by spring, and oak leaves still form a loose forest floor in spring.

In accordance with the ideas of L.G. Ramenskiy about the ecological individuality of species and taking into account the fact that plant species in the community participate in different ways in the development and transformation of the environment and transformation of energy, it can be assumed that in the existing phytocenoses, each plant species has its own ecological niche ...

In ontogeny, plants, like many animals, change their ecological niche. As they age, they use and transform the environment more intensively. The transition of a plant to the generative period significantly expands the range of consorts, changes the size and intensity of the phytogenic field. The environment-forming role of aging, senile plants is decreasing. They lose many consorts, but the role of their associated destructors increases. Production processes are weakened.

In plants, there is an overlap of ecological niches. It increases in certain periods when environmental resources are limited, but since species use resources individually, selectively and with different intensities, competition in stable phytocenoses is weakened.

Rice. 94. Correlation between the diversity of deciduous layers and the species diversity of birds (Shannon MacArthur indices from E. Pianca, 1981)

7.5. Coenotic Species Strategies

In phytocenology, classifications of plants have been developed according to their ability to grow together and coenotic significance. The general provisions of these classifications can be applied to animals, since they characterize a kind of strategies of species that determine their place in biocenoses. Most commonly used system of L. G. Ramensky and D. Grime.

Groups of plants that occupy a similar position in phytocenoses are called phytocoenotypes. L. G. Ramenskiy proposed to distinguish three types among co-living plants - violets, patents and explents. He popularly characterized them as siloviki, hardy and performing (i.e., filling free space), likening them to lions, camels and jackals. Violent have a high competitive ability in these conditions: "while vigorously developing, they capture the territory and hold it for themselves, suppressing, drowning out rivals with the energy of life and the full use of environmental resources." Patents "In the struggle for existence ... they take it not by the energy of vital activity and growth, but by their endurance to extremely harsh conditions, permanent or temporary." They are content with the resources that remain from the violets. Explorents "Have a very low competitive power, but they are able to very quickly capture the liberated territories, filling the gaps between strong plants, they are just as easily displaced by the latter."

More detailed classifications also distinguish other, intermediate types. In particular, one can also distinguish between the group pioneer species that quickly occupy newly emerging areas that have not yet had any vegetation. Pioneer species partially possess the properties of explents - low competitiveness, but, like patents, they have high endurance to the physical conditions of the environment.

In the 70s of the last century, 40 years after L.G. Ramenskiy, the identification of the same three phytocoenotypes was repeated by the botanist D. Greim, unfamiliar with his classification, denoting them with other terms: competitors, tolerants and ruderals.

Almost in any group of organisms, species similar in their ability to coexist are distinguished, therefore, the classification of coenotic strategies of Ramensky-Greim can be attributed to general ecological.

PRACTICAL WORK 6

1. Complete the following definition: “A biocenosis is a collection of organisms:

1.1. one species living in a certain area ______________

1.2. of different species living together and related to each other _______

1.3. of the same species inhabiting heterogeneous areas of the range ___________

1.4. one species inhabiting the same biogeographic area _______

2. Insert the missing words in the following sentences. The complex of co-living and related species is called _____________________. The position that a species occupies in the biocenosis is called ____________________. It is characterized by the ranges of conditions in which organisms of this species live normally, the nature of connections with other species, and the way of life. Species living together may have partially overlapping ____________________, however, they never completely coincide, since the law comes into force and one species displaces the other from ____________________________________.

3. Different types of bark beetles are closely related to certain species of trees. In addition, on the same tree, some species of beetles inhabit the trunk in the lower part, others in the upper part, and third species live only on branches or on the roots. Explain the importance of differences in the selection of sites for insects _____________________

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4. In some farms, both carp and ducks are bred in the same ponds. At the same time, fish production does not decrease, but increases. Offer your explanation for this fact ____________________________

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5. Layering as a structural phenomenon is inherent in many biocenoses. On a longitudinal cut, any biocenosis resembles a multi-storey building. Name the "floors" and their number in a mixed forest, in a spruce forest, in a cereal-clover meadow ___________________________________________

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6. Calculate the index of similarity of two phytocenoses (plant components of biocenoses) using Jaccard's formula: K = C x 100% / (A + I) - C; where A is the number of species of this group in the first community, B is the number of species of this group in the second community, and C is the number of species common to both communities. The index is expressed as a percentage of similarity .________________________________________________________

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The first phytocenosis is located in the reserve and includes the following species: pedunculate oak, linden, hazel, hairy sedge, male fern, Schultes bedstraw, and common runny.

The second phytocenosis is located in the neighboring forest, where people rest, and includes the following types of plants: pedunculate oak, domestic apple, linden, medicinal dandelion, plantain, hairy sedge, wild strawberry, common bilberry, dioecious nettle, bird mountaineer, large burdock, succession ...

Write down the names of the species that disappeared from the oak forest community under the influence of trampling _______________________________________

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Write down the names of the species that appeared in the oak forest due to trampling and other processes accompanying the rest of people in the forest ________________________________________________________________

Write down against each name of a plant species its brief ecological characteristics (preferred biotopes, relation to anthropogenic factors) ________________________________________________________________________________________________________________________________

Tasks in the test form on the topic "Biocenosis and its stability"

1. Biocenosis is called:

a) a set of organisms and habitats associated with the circulation of substances;

b) a group of organisms living together of the same species;

c) a set of co-living organisms belonging to different species;

d) a complex of landscape and soil and climatic conditions of a given habitat.

2. With a close composition of fauna and flora, there are:

a) communities that differ in the set of soil organisms;

b) similar, regularly recurring biocenoses;

c) communities close in the rate of circulation of substances;

d) biocenoses, distinguished by a set of biotic connections.

3.

a) hazel grouse, chiffchaff warbler;

c) wild boar, yellow-throated mouse;

d) praying mantis, badger.

4. The area of ​​the abiotic environment occupied by the biocenosis is called:

a) an ecotope;

b) area;

c) ecosystem;

d) biotope.

5. The ecological niche of the species is called:

a) part of the biotope used for food extraction;

b) a set of habitat conditions;

c) the position of the species in the biocenosis;

d) the regular distribution of individuals of the species.

6. Biocenosis is called:

a) a complex of landscape and soil and climatic conditions of a given habitat;

b) a set of co-living and interconnected organisms belonging to different species;

c) a set of organisms and habitats;

d) a group of organisms living together of the same species.

7.

a) blueberries, green mosses;

b) maple, hazel;

c) white lily, curly pond;

d) European larch, high juniper.

8. In the strip of deciduous forests in different oak forests, there are such animals as:

a) hazel grouse, bank vole;

b) blue tit, acorn weevil;

c) praying mantis, crossbill;

d) sable, squirrel.

9. The species structure of the biocenosis is understood as:

a) distribution of individuals of different species by longline;

b) the variety of species, the ratio of their numbers;

c) the relationship between individuals of different species;

d) the ratio of the number of individuals of different age groups.

10. The spatial structure of the biocenosis is primarily determined by:

a) the ratio of the biomass of producers and consumers;

b) the placement of individuals of different species relative to each other;

c) the ratio of the number of males and females;

d) distribution of individuals of different ages over the tiers.

11. Biocenosis is called:

a) a complex of organisms and habitats, united by the circulation of substances and the flow of energy;

b) a set of organisms and a natural landscape complex;

c) the natural system, which is supported by connections between individuals of different species;

d) a set of individuals of the same species, jointly inhabiting the territory, freely interbreeding and bearing fertile offspring.

12. In the strip of deciduous forests in different oak forests, there are such plants as:

a) blueberries, green mosses;

b) white lily, curly pond;

c) European larch, high juniper;

d) runny, oak anemone.

13. In the strip of deciduous forests in different oak forests, there are such animals as:

a) pied flycatcher, jay;

b) bank vole, tit-tit;

c) speckled gopher, crossbill;

d) peregrine falcon, squirrel.

14. The species are called dominants of the community:

a) strongly affecting the habitat;

b) prevailing in number;

c) characteristic only for a given biocenosis;

d) persisting when changing biocenoses.

15 ... The most vulnerable parts of the biocenosis are:

a) numerous types;

b) dominant species;

c) few species;

d) environment-forming species.

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