Biocenosis is a complex of living interconnected organisms

STRUCTURE OF BIOCENOSIS

What are biocenoses

Groups of co-living and mutually related organisms are calledbiocenoses. The adaptability of members of a 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 term “biocenosis” is more often used in relation to the population of territorial areas that are distinguished on land by relatively homogeneous vegetation (usually along the boundaries of plant associations), for example, the biocenosis of spruce-sorrel forest, the biocenosis of upland meadow, white moss pine forest, the biocenosis of feather grass steppe, wheat field etc.). This refers to the entire set of living beings - plants, animals, microorganisms, adapted to living together in a given territory. In the aquatic environment, biocenoses are distinguished that correspond to the ecological divisions of parts of reservoirs, for example, biocenoses of coastal pebble, sandy or silty soils, and abyssal depths.

STRUCTURE OF BIOCENOSIS

1.Species structure of the biocenosis.

Under species structure biocenosis understand the diversity of species in it and the ratio of their numbers or mass. There are species-poor and species-rich biocenoses. In the polar arctic deserts and northern tundras with extreme heat deficiency, in waterless hot deserts, in reservoirs heavily polluted by sewage, wherever one or several environmental factors deviate far from the average optimal level for life, communities are greatly impoverished, since only a few species can adapt to such extreme conditions. Wherever abiotic conditions approach the average optimum for life, extremely species-rich communities emerge. Examples of these include tropical forests, Coral reefs with their diverse populations, river valleys in arid dry regions, etc.

The species composition of biocenoses, in addition, depends on the duration of their existence. Young, just emerging communities usually include a smaller set of species than long-established, mature ones. Biocenoses created by humans (fields, vegetable gardens, orchards) are also poorer in species than similar natural systems (forest, steppe, meadow. However, even the most impoverished biocenoses include at least several dozen species of organisms belonging to different systematic and ecological groups.

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 (in an anaerobic environment, at the bottom of a reservoir, in rotting sludge). Species-rich natural communities include thousands and even tens of thousands of species, combined complex system relationships.

The influence of a variety of conditions on the diversity of species is manifested, for example, in the so-called "borderline", or edge , effect. It is well known that the vegetation on the edges is usually lush and richer, nesting more types birds, there are more species of insects, spiders, etc. than in the depths of the forest. The conditions of illumination, humidity, and temperature are more varied here. The stronger the differences between two neighboring biotypes, the more heterogeneous the conditions at their boundaries and the stronger the border effect. Species richness increases greatly in places of contact between forest herbaceous, aquatic and land communities, etc.

The species that predominate in numbers are dominants communities. For example, in our spruce forests spruce dominates among the trees, wood sorrel and other species dominate in the grass cover, wren, robin, and chiffchaff dominate among the bird population, bank voles and red-gray voles dominate among mouse-like rodents, etc. However, not all dominant species have the same effect on the biocenosis. Among them, those stand out that, through their vital activity, to the greatest extent create the environment for the entire community and without which, therefore, the existence of most other species is impossible. Such species are called edifiers. 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.). In some cases, animals can also be edificators. For example, in territories occupied by marmot colonies, it is their digging activity that mainly determines the nature of the landscape, microclimate, and plant growth conditions.

In addition to a relatively small number of dominant species, biocenoses include many small and rare forms. They create its species richness, increase the diversity of biocenotic connections and serve as a reserve for the replenishment and replacement of dominants, i.e. give the biocenosis stability and ensure the reliability of its functioning in different conditions. The greater the reserve of such minor species in a community, the greater the likelihood that among them there will be those that can play the role of dominants in the event of any changes in the environment.

The more specific the environmental conditions, the poorer the species composition of the community and the higher the number individual species. In the richest biocenoses, almost all species are small in number.

The diversity of a biocenosis is closely related to its stability: the higher the species diversity, the more stable the biocenosis . Human activity is greatly reducing diversity in natural communities.

2. Spatial structure .

The spatial structure of the biocenosis is determined first
in total, the composition of its plant part - phytocenosis, the distribution of above-ground and underground plant masses. Phytocenosis often acquires a clear longline addition : The assimilating above-ground plant organs and their underground parts are arranged in several layers, using and changing the environment in different ways. Layering is especially noticeable in forests temperate zone. For example, in spruce forests the tree, herb-shrub and moss layers are clearly distinguished. 5-6 tiers can be distinguished in broad-leaved forest: the first, or upper, tier is formed by trees of the first size (pedunculate oak, heart-shaped linden, sycamore maple, smooth elm, etc.); the second - trees of the second size (common mountain ash, wild apple and pear trees, bird cherry, goat willow, etc.); the third tier is the undergrowth formed by shrubs (common hazel, brittle buckthorn, forest honeysuckle, European euonymus, etc.); the fourth consists of tall grasses(wrestlers, spreading pine forest, forest chist, etc.); the fifth tier is made up of lower herbs (common sedge, hairy sedge, perennial grass, etc.); in the sixth tier - the lowest grasses, such as European hoofed grass.

In forests there are always inter-tiered (extra-tiered) plants - these are algae and lichens on the trunks and branches of trees, higher spore-bearing and flowering epiphytes, lianas, etc. Layering allows plants to more fully use the light flux: under the canopy tall plants shade-tolerant, even shade-loving, can exist, intercepting even the weak sunlight. Vegetation layers can be of different lengths: the tree layer, for example, is several meters thick, and the grass cover is only a few centimeters thick. Each tier participates in the creation of phytoclimate in its own way and is adapted to a certain set of conditions.

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

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, among insects there are the following groups: inhabitants of the soil - geobius , ground, surface layer - herpetobium , , moss layer - bryobium, grass stand - phyllobium, higher tiers - aerobium.

Dismemberment in the horizontal direction is mosaic. Mosaic due to a number of reasons: heterogeneity of microrelief, soils, environment-forming influence of plants and their environmental features. It can arise as a result of animal activity (formation of soil emissions and their subsequent overgrowing, formation of anthills, trampling and eating of grass by ungulates, etc.) or humans (selective felling, fire pits, etc.), due to tree fallouts during hurricanes, etc. Changes in the environment under the influence of the vital activity of individual plant species create the so-called phytogenic mosaic.

3. Ecological structure of the biocenosis.

Different types biocenoses are characterized by a certain ratio environmental groups organisms, which expresses the ecological stricture of the community. Biocenoses with a similar ecological structure may have different species composition, since in them the same ecological niches may be occupied by those that are similar in ecology, but are far from related species. Such types that perform the same , functions in similar biocenoses are called vicarious. For example, the same ecological niche - bison on the prairies North America, antelopes in the savannas of Africa, wild horses and kulans in the steppes of Asia. The ecological structure of biocenoses that develop in certain climatic and landscape conditions is strictly natural. So, for example, in biocenoses of different natural areas The ratio of phytophages and saprophages changes naturally. In steppe, semi-desert and desert areas, animal phytophages predominate over saprophages; in forest communities of the temperate zone, on the contrary, saprophagy is more developed. The main type of feeding of animals in the depths of the ocean is predation , whereas in the illuminated, surface zone of the pelagic there are many filter feeders that consume phytoplankton or species with a mixed feeding pattern.

Ecological structure communities also reflects the ratio of such groups of organisms as hygrophytes, mesophytes and xerophytes among plants or hygrophiles, mesophylls and xerophytes among animals. It is quite natural that in dry arid conditions the vegetation is characterized by a predominance of sclerophytes and succulents, while in highly moist biotopes hygro- and even hydrophytes are more abundant.

The relationship of organisms in the biocenosisX.

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

1.Trophic connections occur when one species feeds on another ­ gim-either living individuals, or their dead remains, or waste products. Dragonflies that catch other insects in flight, dung beetles that feed on the droppings of large ungulates, and bees that collect plant nectar enter into a direct trophic relationship with species that provide food. In the case of competition between two species over food objects, an indirect trophic relationship arises between them, since the activity of one affects the food supply of the other. Any effect of one species on the eatability of another or the availability of food for it should be regarded as an indirect trophic relationship between them. For example, caterpillars of nun butterflies, eating pine needles, make it easier for bark beetles to gain access to weakened trees.

Topical and trophic connections have highest value in the biocenosis, form the basis of its existence. It is these types of relationships that keep organisms close to each other different types, uniting them into fairly stable communities of different scales.

3. Phoric connections. This is the participation of one species in the spread of another. Animals act as transporters. The transfer of seeds, spores, and plant pollen by animals is called zoochory; the transfer of other smaller animals is called zoochory. phoresia. Animals can capture plant seeds in two ways: passive and active. Passive capture occurs when an animal's body accidentally comes into contact with a plant, the seeds or infructescences of which have special hooks, hooks, and outgrowths (straw, burdock). The active method of capture is eating fruits and berries. Animals excrete seeds that cannot be digested along with their droppings. Animal phoresia is widespread mainly among small arthropods, especially in various different groups ticks. It is one of the methods of passive dispersal and is characteristic of species for which transfer from one biotope to another is vital for preservation or prosperity. Dung beetles sometimes crawl with raised elytra, which they are unable to fold due to mites densely littering their bodies. Among large animals, phoresia is almost never found.

4. Factory connections . This is a type of biocenotic relationship into which a species enters, using excretory products, either dead remains, or even living individuals of another species for its constructions (fabrication). So birds use tree branches, mammal fur, grass, leaves, down and feathers of other bird species, etc. to build nests. The megachila bee places eggs and supplies in cups constructed from soft leaves various shrubs (rose hips, lilac, acacia, etc.).

• A biocenosis is a historically established collection of animals, plants, fungi and microorganisms that inhabit a relatively homogeneous living space (a certain area of ​​land or water area) and are interconnected by their environment. Biocenoses arose on the basis of the biogenic cycle and ensure it in specific natural conditions. Biocenosis is a dynamic system capable of self-regulation, the components of which (producers, consumers, decomposers) are interconnected. One of the main objects of ecology research.

  The most important quantitative indicators of biocenoses are biodiversity (the total number of species in it) and biomass (the total mass of all types of living organisms in a given biocenosis).

  Biodiversity is responsible for the equilibrium state of the ecosystem, and therefore for its sustainability. Closed cycle nutrients(biogens) occurs only thanks to biological diversity. Substances that are not assimilated by some organisms are assimilated by others, therefore the output of nutrients from the ecosystem is small, and their constant presence ensures the balance of the ecosystem.

  The term (German: Biocönose) was introduced by Karl Möbius in the 1877 book “Die Auster und die Austernwirthschaft” to describe all the organisms that inhabit a certain territory (biotope) and their relationships.

  Types of biocenosis structures: species, spatial (vertical (tiered) and horizontal (mosaic) organization of the biocenosis) and trophic.

  Groups of organisms different sizes live in a biocenosis at different scales of space and time. For example, life cycles single-celled organisms can occur within an hour, and the life cycles of large plants and animals extend over tens of years.

  Biotopes are characterized by a certain species diversity - a set of populations included in its composition. The number of species depends on the duration of existence, climate stability, and productivity of the type of biocenosis (desert, tropical forest).

  The number of individuals of different species varies, etc. The most numerous species biotopes are called dominant. When studying large biotopes, it is impossible to determine all species diversity. For study, the number of species from a certain territory (area) is determined - species richness. The species diversity of different biocenoses is compared by species richness from the same area.

  The species structure gives an idea of ​​the qualitative composition of the biocenosis. When two species exist together in a homogeneous environment under constant conditions, one of them is completely replaced by the other. Competitive relationships arise. Based on such observations, the principle of competitive exclusion, or Gause's principle, was formulated.

  Human activity greatly reduces the diversity in natural communities, which requires forecasts and predictions of its consequences, as well as effective measures to maintain natural systems.

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§ 5. Biocenosis. Diversity of biocenoses

The concept of biocenosis. Living organisms are found on Earth not in any random combinations, as independent individuals, but form regular complexes (communities). For the first time, the German biologist Karl August Moebius (1825-1908) drew attention to the possibility of identifying such communities. In 1877, he proposed the term biocenosis (from Greek bios- life and koinos- general, to make something common).

Biocenosis - this is a historically established group of plants, animals, fungi and microorganisms inhabiting a relatively homogeneous living space (a piece of land or a body of water) (rice. 2.1).

So, each biocenosis consists of a certain set of living organisms belonging to different species. But we know that individuals of the same species are combined into natural systems called populations. Therefore, biocenosis can also be defined as the totality of populations of all types of living organisms inhabiting common habitats.

The composition of the biocenosis includes a set of plants on certain territory - phytocenosis (from Greek phyton- plant), a set of animals living within the phytocenosis, - zoocenosis (from Greek zoon- animal), microbiocenosis - a set of microorganisms inhabiting the soil, and mycocenosis (from Greek mykes- mushroom) - a collection of mushrooms. Examples of biocenoses are deciduous, spruce, pine or mixed forest, meadow, swamp, etc.

Each biocenosis develops within a homogeneous space, which is characterized by a certain combination of abiotic factors, such as the amount of incoming solar radiation, temperature, humidity, chemical and mechanical composition of the soil, its acidity, terrain, etc. Such a homogeneous space (part of the abiotic environment) occupied by biocenosis is called biotope. This could be any piece of land or body of water, the seashore or the slope of a mountain. A biotope is an inorganic environment that is a necessary condition for the existence of a biocenosis. There is a close interaction between biocenosis and biotope.

The scale of biocenoses can be different - from communities of lichen cushions on tree trunks, moss hummocks in a swamp or a decaying stump to the population of entire landscapes. Thus, on land, one can distinguish the biocenosis of a dry meadow (not flooded with water), the biocenosis of a white moss pine forest, the biocenosis of feather grass steppe, the biocenosis of a wheat field, etc.

IN aquatic environment biocenoses are usually distinguished in accordance with the ecological divisions of water bodies - biocenosis of coastal sandy or

silty soils, biocenosis of the tidal zone of the sea, biocenosis of large aquatic plants of the coastal zone of the lake, biocenosis of a fresh reservoir, etc. (Fig. 2.2).

A specific biocenosis includes not only organisms that permanently inhabit a certain territory, but also those that have a significant impact on its life, although they live in other biocenoses.

For example, many insects breed in bodies of water, where they are an important source of food for fish and some other animals. At a young age, they are part of the aquatic biocenosis, and as adults they lead a terrestrial lifestyle, i.e. act as elements of land biocenoses. Hares can eat in the meadow and live in the forest. The same applies to many species of forest birds that seek food not only in the forest, but also in adjacent meadows or swamps.

Species structure of the biocenosis. Each biocenosis can be described based on the totality of its constituent species. The species diversity of different biocenoses is different, which is due to their different geographical locations. It has been established: it decreases in the direction from the tropics towards high latitudes, which is explained by the deterioration of the living conditions of organisms.

For example, in humid tropical forests In Malaysia, up to 200 species of tree species can be counted per 1 hectare of forest. The biocenosis of a pine forest in the conditions of Belarus can include a maximum of ten species of trees per 1 hectare, and in the north of the taiga region there are 2-5 species on the same area. The poorest biocenoses in terms of the set of species are alpine and arctic deserts, the richest are tropical forests.

If any species of plant (or animal) quantitatively predominates in a community (has greater biomass, productivity or numbers), then this species is called dominant, or dominant.

There are dominant species in any biocenosis. In the oak grove these are mighty oaks. Using the main share solar energy and increasing the greatest biomass, they shade the soil, weaken air movement and create special conditions for the life of other forest inhabitants.

However, in addition to oaks, a large number of other organisms live in the oak forest. For example, earthworms living here improve physical and Chemical properties soil, passing particles of dead plants and fallen leaves through the digestive system. The oak and the worm make their own special contribution to the life of the biocenosis, but the role of the oak here is decisive, since the entire life of the oak forest is determined by this tree species and the plants associated with it. Therefore, oak is the dominant species in such a forest.

Spatial structure of the biocenosis. Species are distributed in space in accordance with their needs and habitat conditions. This distribution in space of the species that make up the biocenosis is called spatial structure of the biocenosis. There are vertical and horizontal structures of the biocenosis.

Vertical structure of biocenosis formed by its individual elements, special layers called tiers. Tier - co-growing groups of plant species, differing in height and position in the biocenosis of assimilating organs (leaves, stems, underground organs - tubers, rhizomes, bulbs, etc.). As a rule, different tiers are formed by different life forms (trees, shrubs, shrubs, herbs, mosses). The layering is most clearly expressed in forest biocenoses (Fig. 2.3). So, the first tier here is usually formed by the largest trees with highly located foliage, which is well illuminated by the sun. Unused light can be absorbed by smaller trees, forming a second, sub-canopy layer. About 10% solar radiation intercepted by the undergrowth layer, which is formed by various shrubs, and only from 1 to 5% by grass plants (herb-shrub layer).

The ground layer of mosses and lichens forms the moss-lichen layer. So, schematically, 5 tiers are distinguished in the forest biocenosis.

Similar to the distribution of vegetation, different animal species in biocenoses also occupy certain levels (Fig. 2.4). Soil worms, microorganisms, and digging animals live in the soil. Various centipedes, ground beetles, mites and other small animals live in leaf litter and on the soil surface. Birds nest in the upper canopy of the forest, and some can feed and nest below the upper tier, others in bushes, and still others near the ground. Large mammals live in the lower tiers.

Tiering is also observed in the biocenoses of oceans and seas. Different types of plankton stay at different depths, depending on the lighting, and different types of fish, depending on where they find food.

Living organisms are distributed unevenly in space. They usually form groups, which is an adaptive factor in their lives. Such groupings of organisms determine horizontal structure of the biocenosis.

Dissection in the horizontal direction - mosaic - is characteristic of almost all biocenoses. There are many examples of such a distribution. Many species of fish move from place to place in huge schools. Waterfowl and passerines gather in large flocks, preparing for long-distance flights. North American caribou form huge herds in tundra conditions. In the South American tropics, groups of ants, armed with powerful jaws and stings, line up in a 20-meter wide front and go on the attack, exterminating everyone who hesitates and is unable to escape.

The same examples can be given for plants: a spotted distribution of clover individuals in a meadow, spots of mosses and lichens, a cluster of lingonberry shrubs in a pine forest, extensive spots of sorrel in a spruce forest, strawberry glades on light edges.

The presence of mosaics is important for the life of the community. Mosaicism allows for more complete use of different types of microhabitats. Individuals forming groups are characterized by high survival rates and use food resources most efficiently. This leads to an increase in the number and diversity of species in the biocenosis, contributing to its stability and viability.

Relationships between organisms in biocenoses. Individuals of different species do not exist in biocenoses in isolation; they enter into various direct and indirect relationships with each other. Direct relationships are divided into four types: trophic, topical, phoric, factory.

Trophic relationships arise when one species in a biocenosis feeds on another (either the dead remains of individuals of this species, or the products of their vital activity). A ladybug feeding on aphids, a cow in a meadow eating lush grass, a wolf hunting a hare - these are all examples of direct trophic connections between species.

Topical relations characterize changes in the living conditions of one species as a result of the life activity of another. Spruce, shading the soil, displaces light-loving species from under its crown, crustaceans settle on the skin of whales, mosses and lichens are located on the bark of trees. All these organisms are connected to each other by topical connections.

Phoric relations - participation of one species in the spread of another. This role is usually played by animals that carry seeds, spores, and pollen. Thus, the seeds of burdock or string, which have clinging thorns, can be captured by the fur of large mammals and transported over long distances.

Factory relations - a type of relationship in which individuals of one species use excretory products, dead remains, or even living individuals of another species for their structures. For example, birds build nests from dry twigs, grass, mammal fur, etc. To build their houses, caddisfly larvae use pieces of sand bark, fragments of shells, or the shells themselves with live small species of mollusks.

Of all the types of biotic relationships between species in a biocenosis, topical and trophic connections are of greatest importance, since they hold organisms of different species near each other, uniting them into fairly stable communities of different scales.

Biocenoses can vary in size - from small (a hummock in a swamp, an anthill, cushions of lichens on tree trunks, a small pond) to very large (biocenosis of a forest, meadow, lake, swamp, feather grass steppe).

Biocenoses most often do not have clear boundaries. In nature, they transform into each other gradually, making it impossible to determine where one biocenosis ends and another begins. For example, the biocenosis of a dry forest gradually turns into a biocenosis of a moist meadow, which is replaced by a swamp. Visually, we can distinguish the forest biocenosis from the meadow and swamp, but we are not able to clearly say where the boundary line lies. In the vast majority of cases, we will be dealing with a kind of transitional strip of varying width and length, because hard, sharp boundaries in nature are a rare exception. Such the transitional strip (or zone) between adjacent physiognomically distinct communities is called an ecotone.

Historically established groups of co-living and interconnected organisms of different species are called biocenoses. The composition of the biocenosis includes phytocenosis, zoocenosis, mycocenosis and microrobocenosis. Each biocenosis is characterized by species and spatial (vertical and horizontal) structure and various biotic relationships of organisms.

The collection of living beings that are part of ecological system, is called a biotic community, or biocenosis. Hence, biocenosis- the totality of populations of all types of living organisms inhabiting a certain geographical area, differing from other neighboring territories in chemical composition soils, waters, as well as a number of physical indicators(altitude above sea level, amount of solar radiation, etc.). This refers to the entire set of living beings - plants, animals, microorganisms, adapted to living together in a given territory. The concept of “biocenosis” is one of the most important in ecology, since it follows from it that living beings form complexly organized systems on Earth, outside of which they cannot exist sustainably. The main function of the community is to ensure balance in the ecosystem based on a closed cycle of substances.

Biocenoses can include thousands of species of different organisms. But not all of them are equally significant. Removing some of them from the community has no noticeable effect on them, while removing others leads to significant changes.

Some types of biocenosis may be represented by numerous populations, while others may be small. The scale of biocenotic groups of organisms varies greatly - from communities of lichen cushions on tree trunks or a decaying stump to populations of entire landscapes: forests, steppes, deserts, etc.

The organization of life at the biocenotic level is subordinated to hierarchy. As the scale of communities increases, their complexity and the proportion of indirect, indirect connections between species increase.

Natural associations of living beings have their own laws of functioning and development, i.e. are natural systems.

Thus, being, like organisms, structural units of living nature, biocenoses nevertheless develop and maintain their stability on the basis of other principles. They are systems of the so-called frame type- without special management and coordinating centers, and are also built on numerous and complex internal connections.

The most important features of systems related to the inorganic level of life organization, for example, according to the classification of the German ecologist V. Tishler, are the following:

• Communities always arise, are made up of ready-made parts (representatives various types or entire complexes of species) present in the environment. In this way, the way they arise differs from the formation of a separate organism, which occurs through gradual differentiation of the simplest initial state.
• Community parts are interchangeable. The parts (organs) of any organism are unique.
• If the whole organism maintains constant coordination and consistency in the activities of its organs, cells and tissues, then the supraorganismal system exists mainly due to the balancing of oppositely directed forces.
• Communities are based on the quantitative regulation of the numbers of some species by others.
• The maximum size of an organism is limited by its internal hereditary program. The dimensions of supraorganismal systems are determined by external factors.

Within the phytocenosis, each species behaves relatively independently. From the standpoint of continuity, species are found together not because they have adapted to each other, but because they have adapted to general environment a habitat. Any variation in habitat conditions causes changes in community composition.

It is multifaceted, and when studying it, various aspects are highlighted.

Species and spatial structure of the biocenosis

There are concepts of “species richness” and “species diversity” of biocenoses. Species richness- a general set of community species, which is expressed by a list of representatives of different groups of organisms. Species diversity- an indicator that reflects not only the qualitative composition of the biocenosis, but also the quantitative relationships of species.

There are species-poor and species-rich biocenoses. The species composition of biocenoses, in addition, depends on the duration of their existence and the history of each biocenosis. Young, just emerging communities usually include a smaller set of species than long-established, mature ones. Biocenoses created by humans (fields, gardens, orchards) are also poorer in species than similar natural systems (forests, steppes, meadows). Man maintains the monotony and species poverty of agrocenoses with a special complex system of agrotechnical measures.

Almost all terrestrial and most aquatic biocenoses include both plants and animals. The stronger the differences between two neighboring biotopes, the more heterogeneous the conditions at their boundaries and the stronger the border effect. Number of a given group of organisms in biocenoses strongly depends on their size. The smaller the individuals of a species, the higher their numbers in biotopes.

Groups of organisms of different sizes live in biocenoses at different scales of space and time. For example, the life cycles of single-celled organisms can take place within an hour, while the life cycles of large plants and animals extend over tens of years.

Naturally, in all biocenoses the smallest forms - bacteria and other microorganisms - predominate numerically. In each community, one can distinguish a group of main species, the most numerous in each size class, the connections between which are decisive for the functioning of the biocenosis as a whole. Species predominant in numbers (productivity) are dominants of the community. Dominants dominate the community and constitute the “species core” of any biocenosis.

For example, when studying a pasture, it was found that the maximum area in it is occupied by a plant - bluegrass, and among the animals grazing there, most of all are cows. This means that bluegrass dominates among producers, and cows dominate among consumers.

In the richest biocenoses, almost all species are small in number. In tropical forests it is rare to find several trees of the same species nearby. There are no outbreaks in such communities mass reproduction individual species, biocenoses are highly stable.

The totality of all types of community constitutes it biodiversity. Typically, a community includes several main species with high abundance and many rare species with a small number.

Biodiversity is responsible for the equilibrium state of the ecosystem, and therefore for its sustainability. A closed cycle of nutrients (biogens) occurs only due to biological diversity. Substances that are not assimilated by some organisms are assimilated by others, therefore the output of nutrients from the ecosystem is small, and their constant presence ensures the balance of the ecosystem.

Human activity greatly reduces diversity in natural communities, which requires forecasts and predictions of its consequences, as well as effective measures to maintain natural systems.

The area of ​​the abiotic environment occupied by a biocenosis is called biotope.

The spatial structure of a terrestrial biocenosis consists of its plant part - phytocenosis, the distribution of above-ground and underground mass of plants. Animals are also predominantly confined to one or another layer of vegetation (Fig. 1).

Rice. 1. Distribution of ungulates by food tiers (De la Fuente, 1972): 1- giraffe; 2 - gerenuk antelope; 3 - dik-dik antelope; 4 - rhinoceros; 5 - elephant; 6 - zebra; 7 - giu; 8 - Grant's gazelle; 9 - antelope hartebeest

Biocenosis is a historically established group of plants, animals, fungi and microorganisms that inhabit one area (a piece of land or a body of water). Biocenoses are formed either on their own or under human influence.

Biocenosis as a term was proposed by Karl Mobius in the 19th century. The existence of a biocenosis can be determined by both biological and physical-geographical features. The composition, structure of the biocenosis, its characteristics depend on various factors, starting from climatic conditions and ending with B different zones the composition and characteristics of biocenoses differ.

Any biocenosis is a collection natural ingredients, having their own species composition. So, say, the biocenosis of a humid tropical forest will be very different from the desert one, that is, the number of species of the biocenosis of the tropics will be much more extensive than in the desert. For formation species composition biocenoses are also influenced by historical factors. For example, older communities have large quantity species than young ones.

Tiering (spatial structure of the biocenosis) is the vertical arrangement of the phytocenosis in the underground and above-ground parts. The structure of the biocenosis has a terrestrial and underground component. All tiers of the biocenosis are characterized by various characteristics: ecological, floristic, morphological, etc. Tiering is well expressed in the forests where it is represented:

• tree layer;
• shrubby;
• shrub-herbaceous;
• layer of mosses and lichens.

Based on the number of tiers, biocenoses are:

• simple;
• complex.

Biocenosis is a complex in which there are permanent connections called food or trophic. On their basis, the trophic structure of a biocenosis presupposes the emergence of food connections in cases where organisms of one species or another feed on the organisms of another species themselves or on the products of their vital activity. Such connections are called direct or indirect. Direct connections are formed due to the absorption of representatives of another by organisms of one species. Indirect connections are formed as a result of competition between organisms of two different species for food.

Biocenosis is a changing structure. It can undergo long-term changes in one direction, which lead to a restructuring of its characteristics, and can also cause the replacement of one biocenosis with another. This process is called succession. Successions are divided into primary and secondary. Primary successions occur in areas not previously inhabited by any biocenosis. Secondary successions occur on the site of disappeared or destroyed biocenoses. The final stage of the life activity of a phytocenosis is called menopause. Succession is usually divided into the following types:

• syngenesis (changes caused by the interaction of plants);
• endoecogenesis (changes that occurred as a result of the life activity of the phytocenosis itself);
• exoecogenesis (changes caused by the actions of natural factors external to the phytocenosis).

These types are in turn divided into:

• climatogenic;
• edaphogenic;
• zoogenic;
• anthropogenic.

Under the influence of successions, a stable phytocenosis can be restored or formed, or, conversely, regress.

The dominant environmental factors are determined by the division of zones according to temperature distribution environment and the amount of precipitation. As the distance from the equator increases, natural zones change. Within the limits, impacts occur, called extrazonal and intrazonal, which are determined by the influence of relief, hydrological objects and other factors.