Structure of Antibodies Now let's briefly look at the structure of the antibody molecule. All antibodies have a common structure - they are proteins consisting of several subunits. In Fig. Figure 3.2 shows the structure of the most common antibody, called IgG. This structure was first described in

5. Species: criteria and structure Remember! What levels of organization of living nature do you know? What is a species? What other systematic categories do you know? Charles Darwin’s evolutionary theory is based on the idea of ​​a species. What is a species and how real is it?

24. Structure of ecosystems Remember! What levels of organization of living nature do you know? What is an ecosystem? The influence of abiotic factors on living organisms and interactions between individual species underlie the life of any community. A community, or biocenosis, is

3.3. Chromosome structure Each chromatid contains one DNA molecule associated with histone and non-histone proteins. Currently, the nucleosome model of eukaryotic chromatin organization is accepted (Kornberg R., 1974; Olins A., Olins D., 1974). According to this model, histone proteins (they

Biocenosis— a set of populations of plants, animals and microorganisms. The place occupied by a biocenosis is called a biotope. The species structure of a biocenosis covers all species living in it. The spatial structure includes a vertical structure - tiers and a horizontal structure - microcenoses and microassociations. The trophic structure of the biocenosis is represented by producers, consumers and decomposers. The transfer of energy from one species to another by eating them is called a food (trophic) chain. The place of an organism in the food chain, associated with its food specialization, is called the trophic level. The trophic structure of a biocenosis and ecosystem is usually displayed by graphic models in the form of ecological pyramids. There are ecological pyramids of numbers, biomass and energy. The rate of solar energy fixation determines the productivity of biocenoses. The set of environmental factors within which a species lives is called an ecological niche. The tendency to increase the diversity and density of living organisms at the boundaries of biocenoses (in ecotones) is called the edge effect.

The concept of biocenosis

Organisms do not live on Earth as independent individuals. They form regular complexes in nature. German hydrobiologist K. Möbius in the late 70s. XIX century studied complexes of bottom animals - clusters of oysters (oyster banks). He observed that, along with oysters, there were also animals such as starfish, echinoderms, bryozoans, worms, ascidians, sponges, etc. The scientist concluded that these animals live together in the same habitat, not by chance. They need the same conditions as oysters. Such groupings appear due to similar requirements for environmental factors. Complexes of living organisms that constantly meet together at different points of the same water basin under the same conditions of existence were called biocenoses by Mobius. The term “biocenosis” (from the Greek bios - life and koinos - general) was introduced by him into the scientific literature in 1877.

The merit of Möbius is that he not only established the existence of organic communities and proposed a name for them, but also managed to reveal many patterns of their formation and development. Thus, the foundations were laid for an important direction in ecology - biocenology (ecology of communities).

The biocenotic level is the second (after population) supra-organismal level of organization of living systems. A biocenosis is a fairly stable biological formation that has the ability to self-maintain its natural properties and species composition under external influences caused by changes in climatic and other factors. The stability of a biocenosis is determined not only by the stability of its constituent populations, but also by the characteristics of the interaction between them.

- these are historically established groups of plants, animals, fungi and microorganisms that inhabit a relatively homogeneous living space (a piece of land or a body of water).

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

It should be noted that the term “biocenosis” has become widespread in the scientific literature in German and Russian, and in English-speaking countries it corresponds to the term “community”. However, strictly speaking, the term “community” is not synonymous with the term “biocenosis”. If a biocenosis can be called a multi-species community, then a population (an integral part of the biocenosis) is a single-species community.

The composition of a biocenosis includes a set of plants in a certain territory - phytocenosis(from Greek phyton - plant); the totality of animals living within the phytocenosis - zoocenosis(from Greek zoon - animal); microbiocenosis(from the Greek mikros - small + bios - life) - a set of microorganisms that inhabit the soil. Sometimes they include as a separate component element in the biocenosis mycocenosis(from Greek mykes - mushroom) - a collection of mushrooms. Examples of biocenoses are deciduous, spruce, pine or mixed forest, meadow, swamp, etc.

The homogeneous natural living space (part of the abiotic environment) occupied by a biocenosis is called biotope. This could be a piece of land or a body of water, a seashore or a mountainside. A biotope is an inorganic environment that is a necessary condition for the existence of a biocenosis. Biocenosis and biotope closely interact with each other.

The scale of biocenoses can be different - from communities of lichens 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.

A specific biocenosis includes not only organisms that permanently inhabit a certain territory, but also those that have a significant impact on it. For example, many insects breed in bodies of water, where they serve as 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 look for food not only in the forest, but also in adjacent meadows or swamps.

Species structure of biocenosis

Species structure of biocenosis is the totality of its constituent species. In some biocenoses, animal species may predominate (for example, the biocenosis of a coral reef); in other biocenoses, plants play the main role: the biocenosis of a floodplain meadow, feather grass steppe, spruce, birch, and oak forest. The number of species (species diversity) in different biocenoses is different and depends on their geographical location. The most well-known pattern of changes in species diversity is its decrease from the tropics towards high latitudes. The closer to the equator, the richer and more diverse the flora and fauna. This applies to all forms of life, from algae and lichens to flowering plants, from insects to birds and mammals.

In the rain forests of the Amazon basin, on an area of ​​about 1 hectare, you can count up to 400 trees of more than 90 species. In addition, many trees serve as supports for other plants. Up to 80 species of epiphytic plants grow on the branches and trunk of each tree.

An example of species diversity is one of the volcanoes in the Philippines. There are more tree species growing on its slopes than in the entire United States!

Unlike the tropics, the biocenosis of a pine forest in the temperate zone of Europe can include a maximum of 8-10 tree species per 1 hectare, and in the north of the taiga region there are 2-5 species in the same area.

The poorest biocenoses in terms of the set of species are alpine and arctic deserts, the richest are tropical forests. Panama's rainforests are home to three times more species of mammals and birds than Alaska.

A simple indicator of the diversity of a biocenosis is the total number of species, or species richness. If any species of plant (or animal) quantitatively predominates in a community (has greater biomass, productivity, number or abundance), then this species is called dominant, or dominant species(from Latin dominans - dominant). There are dominant species in any biocenosis. For example, in a spruce forest, spruce trees, using the main share of solar energy, increase the greatest biomass, shade the soil, weaken air movement and create a lot of inconvenience for the lives of other forest inhabitants.

Spatial structure of the biocenosis

Species can be distributed differently in space according to their needs and habitat conditions. This distribution of species that make up the biocenosis in space is called spatial structure of the biocenosis. There are vertical and horizontal structures.

Vertical structure a biocenosis is formed by its individual elements, special layers called tiers. Tier - co-growing groups of plant species that differ 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. 1).

First, woody, tier usually consists of tall trees with high-mounted foliage that is well illuminated by the sun. Unused light can be absorbed by trees, forming a second, subcanopy, tier.

Understory layer are made up of shrubs and shrubby forms of tree species, for example hazel, rowan, buckthorn, willow, forest apple, etc. In open areas under normal environmental conditions, many shrubby forms of such species as mountain ash, apple, and pear would have the appearance of trees of the first size. However, under the forest canopy, in conditions of shading and lack of nutrients, they are doomed to exist in the form of low-growing, often non-barking seeds and fruits of trees. As the forest biocenosis develops, such species will never reach the first tier. This is how they differ from the next tier of the forest biocenosis.

Rice. 1. Tiers of forest biocenosis

TO adolescent layer These include young, low (from 1 to 5 m) trees, which in the future will be able to enter the first tier. These are the so-called forest-forming species - spruce, pine, oak, hornbeam, birch, aspen, ash, black alder, etc. These species can reach the first tier and form biocenoses with their dominance (forests).

Under the canopy of trees and shrubs there is herbaceous-shrub layer. This includes forest herbs and shrubs: lily of the valley, oxalis, strawberries, lingonberries, blueberries, ferns.

The ground layer of mosses and lichens forms moss-lichen layer.

So, in the forest biocenosis there are tree stand, undergrowth, undergrowth, grass cover and moss-lichen layer.

Similar to the distribution of vegetation by tiers, in biocenoses different species of animals also occupy certain levels. 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 inherent in the biocenoses of oceans and seas. Different types of plankton stay at different depths depending on the lighting. Different species of fish live at different depths depending on where they find food.

Individuals of living organisms are distributed unevenly in space. Usually they form groups of organisms, which is an adaptive factor in their life. Such groupings of organisms determine horizontal structure of the biocenosis- horizontal distribution of individuals forming various kinds of patterning and spotting of each species.

There are many examples of such distribution: these are numerous herds of zebras, antelopes, elephants in the savannah, colonies of corals on the seabed, schools of sea fish, flocks of migratory birds; thickets of reeds and aquatic plants, accumulations of mosses and lichens on the soil in a forest biocenosis, patches of heather or lingonberries in the forest.

The elementary (structural) units of the horizontal structure of plant communities include microcenosis and microgrouping.

Microcenosis(from the Greek micros - small) - the smallest structural unit of the horizontal division of the community, which includes all tiers. Almost every community includes a complex of microcommunities or microcenoses.

Microgrouping - condensation of individuals of one or several species within a tier, intra-tier mosaic spots. For example, in the moss layer, various moss patches with dominance of one or several species can be distinguished. In the grass-shrub layer there are blueberry, blueberry-sour sorrel, and blueberry-sphagnum microgroups.

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 and diversity of species in the biocenosis, contributing to its stability and viability.

Trophic structure of biocenosis

The interaction of organisms occupying a certain place in the biological cycle is called trophic structure of the biocenosis.

In the biocenosis, three groups of organisms are distinguished.

1.Producers(from Latin producens - producing) - organisms that synthesize from inorganic substances (mainly water and carbon dioxide) all organic substances necessary for life, using solar energy (green plants, cyanobacteria and some other bacteria) or the energy of oxidation of inorganic substances (sulfur bacteria , iron bacteria, etc.). Typically, producers are understood as green chlorophyll-bearing plants (autotrophs) that provide primary production. The total weight of dry matter of phytomass (plant mass) is estimated at 2.42 x 10 12 tons. This constitutes 99% of all living matter on the earth's surface. And only 1% accounts for heterotrophic organisms. Therefore, planet Earth owes its existence to vegetation only to the existence of life on it. It was green plants that created the necessary conditions for the appearance and existence, first, of various prehistoric animals, and then of humans. When they died, the plants accumulated energy in coal deposits, peat and oil sludge.

Producing plants provide humans with food, raw materials for industry, and medicine. They purify the air, trap dust, soften the air temperature, and muffle noise. Thanks to vegetation, there is a huge variety of animal organisms that populate the Earth. Producers constitute the first link in food prices and form the basis of ecological pyramids.

2.Consumers(from Latin consumo - consume), or consumers, are heterotrophic organisms that feed on ready-made organic matter. Consumers themselves cannot build organic matter from inorganic matter and obtain it in finished form by feeding on other organisms. In their organisms, they transform organic matter into specific forms of proteins and other substances, and release waste generated during their life into the environment.

Grasshopper, hare, antelope, deer, elephant, etc. herbivores are consumers of the first order. A toad grabbing a dragonfly, a ladybug feeding on aphids, a wolf hunting a hare - all these are second-order consumers. A stork eating a frog, a kite carrying a chicken into the sky, a snake swallowing a swallow are consumers of the third order.

3. Decomposers(from Latin reducens, reducentis - returning, restoring) - organisms that destroy dead organic matter and transform it into inorganic substances, which, in turn, are absorbed by other organisms (producers).

The main decomposers are bacteria, fungi, protozoa, i.e. heterotrophic microorganisms found in the soil. If their activity decreases (for example, when humans use pesticides), the conditions for the production process of plants and consumers worsen. Dead organic remains, be it a tree stump or the corpse of an animal, do not disappear into nowhere. They are rotting. But dead organic matter cannot rot on its own. Reducers (destructors, destroyers) act as “gravediggers”. They oxidize dead organic residues to C0 2, H 2 0 and simple salts, i.e. to inorganic components, which can again be involved in the cycle of substances, thereby closing it.

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 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 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, united by a complex system of 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 on the edges the vegetation is usually lush and richer, more species of birds nest, more species of insects, spiders, etc. are found 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, wood oxalis and other species dominate in the bird population, kinglets, robin, and chiffchaffs dominate among the mouse-like rodents, bank voles and red-gray voles, etc. However, not all dominant species equally influence 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 of 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 greatly reduces 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 temperate forests. For example, in spruce forests the tree, herb-shrub and moss layers are clearly distinguished. 5-6 tiers can be distinguished in a broad-leaved forest: the first, or upper, tier is formed by trees of the first size (pedunculate oak, cordate 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 (borets, spreading boron, 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 and flowering epiphytes, lianas, etc. Layering allows plants to more fully use the light flux: shade-tolerant, even shade-loving, plants can exist under the canopy of tall plants , intercepting even 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 the following groups are distinguished: soil inhabitants - 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 of biocenoses are characterized by a certain ratio of ecological groups of organisms, which expresses the ecological stricture of the community. Biocenoses with similar ecological structures may have different species composition, since in them the same ecological niches can be occupied by species that are similar in ecology, but are far from related. Such types that perform the same , functions in similar biocenoses are called vicarious. For example, bison in the prairies of North America, antelopes in the savannas of Africa, wild horses and kulans in the steppes of Asia share the same ecological niche. The ecological structure of biocenoses that develop in certain climatic and landscape conditions is strictly natural. For example, in biocenoses of different natural zones the ratio of phytophages and saprophages naturally changes. 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.

The ecological structure of communities is also reflected by 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 are of greatest importance in a biocenosis and 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.

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 common mainly among small arthropods, especially in various groups of mites. 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 the soft leaves of various shrubs (rose hips, lilac, acacia, etc.).

In nature, all living organisms are in constant relationship with each other. What is it called? Biocenosis is an established collection of microorganisms, fungi, plants and animals, which was formed historically in a relatively homogeneous living space. Moreover, all these living organisms are connected not only with each other, but also with their environment. Biocenosis can exist both on land and in water.

Origin of the term

The concept was first used by the famous German botanist and zoologist Karl Moebius in 1877. He used it to describe the collection and relationships of organisms inhabiting a certain territory, which is called a biotope. Biocenosis is one of the main objects of research in modern ecology.

The essence of relationships

Biocenosis is a relationship that has arisen on the basis of the biogenic cycle. It is he who provides it in specific conditions. What is the structure of the biocenosis? This dynamic and self-regulating system consists of the following interconnected components:

• Producers (aphthotrophs), which are producers of organic substances from inorganic ones. Some bacteria and plants, in the process of photosynthesis, convert solar energy and synthesize organic matter, which is consumed by living organisms called heterotrophs (consumers, decomposers). Producers capture carbon dioxide from the atmosphere, which is emitted by other organisms, and produce oxygen.
• Consumers, who are the main consumers of organic substances. Herbivores eat plant foods, in turn becoming lunch for carnivorous predators. Thanks to the digestion process, consumers carry out the primary grinding of organic matter. This is the initial stage of its collapse.
• Decomposers that completely decompose organic matter. They dispose of waste and corpses of producers and consumers. Decomposers are bacteria and fungi. The result of their vital activity is minerals, which are again consumed by the producers.

Thus, it is possible to trace all connections in the biocenosis.

Basic Concepts

All members of the community of living organisms are usually called by certain terms derived from Greek words:

• a set of plants in a specific area - phytocenosis;
• all species of animals living within the same area - zoocenosis;
• all microorganisms living in a biocenosis are microbiocenosis;
• fungal community - mycocenosis.

Quantitative indicators

The most important quantitative indicators of biocenoses:

• biomass, which is the total mass of all living organisms in specific natural conditions;
• biodiversity, which is the total number of species in a biocenosis.

Biotope and biocenosis

In the scientific literature, terms such as “biotope” and “biocenosis” are often used. What do they mean and how do they differ from each other? In fact, the entire set of living organisms that are part of a particular ecological system is usually called a biotic community. Biocenosis has the same definition. This is a collection of populations of living organisms living in a certain geographical area. It differs from others in a number of chemical (soil, water) and physical (solar radiation, altitude, area size) indicators. A section of the abiotic environment occupied by a biocenosis is called a biotope. So both of these concepts are used to describe communities of living organisms. In other words, a biotope and a biocenosis are practically the same thing.

Structure

There are several types of biocenosis structures. They all characterize it according to different criteria. These include:

• The spatial structure of the biocenosis, which is divided into 2 types: horizontal (mosaic) and vertical (tiered). It characterizes the living conditions of living organisms in specific natural conditions.
• The species structure of the biocenosis, responsible for a certain diversity of the biotope. It represents the totality of all populations that are part of it.
• Trophic structure of biocenosis.

Mosaic and tiered

The spatial structure of the biocenosis is determined by the location of living organisms of different species relative to each other in the horizontal and vertical direction. Tiering ensures the fullest use of the environment and an even distribution of species vertically. Thanks to this, their maximum productivity is achieved. So, in any forest the following tiers are distinguished:

• terrestrial (mosses, lichens);
• grassy;
• shrubby;
• arboreal, including trees of the first and second sizes.

The corresponding arrangement of animals is superimposed on the tiers. Thanks to the vertical structure of the biocenosis, plants make full use of the light flux. So, light-loving trees grow in the upper tiers, and shade-tolerant trees grow in the lower ones. Different horizons are also distinguished in the soil depending on the degree of saturation with roots.

Under the influence of vegetation, the forest biocenosis creates its own microenvironment. There is not only an increase in temperature, but also a change in the gas composition of the air. Such transformations of the microenvironment favor the formation and layering of fauna, including insects, animals and birds.

The spatial structure of the biocenosis is also mosaic. This term refers to the horizontal variability of flora and fauna. Mosaic area depends on the diversity of species and their quantitative ratio. It is also influenced by soil and landscape conditions. Often, people create an artificial mosaic by cutting down forests, draining swamps, etc. Because of this, new communities are formed in these territories.

Mosaic character is inherent in almost all phytocenoses. Within their boundaries, the following structural units are distinguished:

• Consortia, which are a set of species united by topical and trophic connections and dependent on the core of this group (central member). Most often, its basis is a plant, and its components are microorganisms, insects, and animals.
• Sinusia, which is a group of species in a phytocenosis, belonging to similar life forms.
• Parcels representing a structural part of the horizontal section of a biocenosis, differing from its other components in its composition and properties.

Spatial structure of the community

A clear example for understanding vertical layering in living beings is insects. Among them are the following representatives:

• soil inhabitants - geobia;
• inhabitants of the surface layer of the earth - herpetobia;
• Bryobia living in mosses;
• phyllobia located in the grass stand;
• aerobia living on trees and shrubs.

Horizontal structuring is caused by a number of different reasons:

• abiogenic mosaic, which includes factors of inanimate nature, such as organic and inorganic substances, climate;
• phytogenic, associated with the growth of plant organisms;
• aeolian-phytogenic, which is a mosaic of abiotic and phytogenic factors;
• biogenic, associated primarily with animals that are able to dig the ground.

Species structure of biocenosis

The number of species in a biotope directly depends on the stability of the climate, the duration of existence and the productivity of the biocenosis. So, for example, in a tropical forest such a structure will be much wider than in a desert. All biotopes differ from each other in the number of species inhabiting them. The most numerous biogeocenoses are called dominant. In some of them, it is simply impossible to determine the exact number of living beings. Typically, scientists determine the number of different species concentrated in a particular area. This indicator characterizes the species richness of the biotope.

This structure makes it possible to determine the qualitative composition of the biocenosis. When comparing territories of equal area, the species richness of the biotope is determined. In science there is the so-called Gause principle (competitive exclusion). In accordance with it, it is believed that if 2 types of similar living organisms exist together in a homogeneous environment, then under constant conditions one of them will gradually displace the other. At the same time, they have a competitive relationship.

The species structure of the biocenosis includes 2 concepts: “richness” and “diversity”. They are somewhat different from each other. Thus, species richness represents the total set of species living in a community. It is expressed by a list of all representatives of different groups of living organisms. Species diversity is an indicator that characterizes not only the composition of the biocenosis, but also the quantitative relationships between its representatives.

Scientists distinguish between poor and rich biotopes. These types of biocenosis differ in the number of community representatives. The age of the biotope plays an important role in this. Thus, young communities that began their formation relatively recently include a small set of species. Every year the number of living creatures in it can increase. The poorest are the biotopes created by man (vegetable gardens, orchards, fields).

Trophic structure

The interaction of various organisms that have their specific place in the cycle of biological substances is called the trophic structure of the biocenosis. It consists of the following components:

Features of biocenoses

Populations and biocenoses are the subject of careful study. Thus, scientists have found that most aquatic and almost all terrestrial biotopes contain microorganisms, plants and animals. They established the following feature: the greater the differences in two neighboring biocenoses, the more heterogeneous the conditions at their boundaries. It has also been established that the number of a certain group of organisms in a biotope largely depends on their size. In other words, the smaller the individual, the greater the number of this species. It has also been established that groups of living creatures of different sizes live in the biotope at different scales of time and space. Thus, the life cycle of some unicellular organisms takes place within one hour, and that of a large animal within decades.

Number of species

In each biotope, a group of main species is identified, the most numerous in each size class. It is the connections between them that are decisive for the normal functioning of the biocenosis. Those species that predominate in numbers and productivity are considered dominant in a given community. They dominate it and are the core of this biotope. An example is bluegrass, which occupies the maximum area in a pasture. She is the main producer of this community. In the richest biocenoses, all types of living organisms are almost always small in number. Thus, even in the tropics, several identical trees are rarely found in one small area. Since such biotopes are distinguished by their high stability, outbreaks of mass reproduction of some representatives of flora or fauna rarely occur in them.

All species of a community constitute its biodiversity. A biotope has certain principles. As a rule, it includes several main species, characterized by high numbers, and a large number of rare species, characterized by a small number of its representatives. This biodiversity is the basis for the equilibrium state of a particular ecosystem and its sustainability. It is thanks to him that a closed cycle of nutrients (nutrients) occurs in the biotope.

Artificial biocenoses

Biotopes are formed not only naturally. In their life, people have long learned to create communities with properties that are useful to us. Examples of biocenosis created by man:

• man-made canals, reservoirs, ponds;
• pastures and fields for agricultural crops;
• drained swamps;
• renewable gardens, parks and groves;
• field-protective forest plantations.

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 a direct threat to the existence of the individual. The entire sum of the influences that living beings have on each other is united by the name biotic environmental factors.

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

Groups of co-living and mutually related species are called biocenoses (from the Latin “bios” - life, “cenosis” - general). 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 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 established that oysters can live only in certain conditions (depth, currents, soil type, water temperature, salinity, etc.) and that a certain set of other species constantly live with them - mollusks, fish, crustaceans, echinoderms, worms , coelenterates, sponges, etc. (Fig. 75). They are all interconnected and influenced by environmental conditions. 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 designate a community in which the sum of species and individuals, constantly limited and subject to selection under the influence of external conditions of life, through reproduction, continuously owns some definite 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 ability of species to coexist with each other for a long time in the same biocenosis is the result of natural selection and 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 groups of organisms is very different, from communities of lichen cushions on tree trunks or a decaying stump to populations of entire landscapes: forests, steppes, deserts, etc.

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

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

B – sand biocenosis: 9 – nemeretines; 10 – Saccocirrus worms; 11 – amphipods; 12 – Venus mollusks; 13 – sultan fish; 14 – flounder; 15 – hermit crabs;

B – biocenosis of zoster thickets: 16 – zoster; 17 – sea needles; 18 - greenfinches; 19 - Sea Horses; 20 - shrimps;

G – oyster biocenosis: 21 – oysters; 22 - scallops;

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

E – biocenosis of phaseolin silt: 27 – mollusk phaseolina; 28 – echinoderm amphiura; 29 – mollusk Trophonopsis;

F – hydrogen sulfide kingdom of bacteria;

H – biocenosis of open sea plankton: 31 – jellyfish, etc.

The term “biocenosis” in modern environmental literature 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 water bodies, for example, biocenoses of coastal pebble, sandy or silty soils, abyssal depths, pelagic biocenoses of large circulations of water masses, etc.

In relation to smaller communities (the population of tree trunks or foliage, moss hummocks in swamps, burrows, anthills, decaying stumps, etc.), various terms are used: “microcommunities”, “biocenotic groups”, “biocenotic complexes”, etc.

There is no fundamental difference between biocenotic groups of different scales. Smaller communities are an integral, albeit relatively autonomous part of larger ones, and they, in turn, are parts of communities of even larger scales. Thus, the entire living population of moss and lichen cushions on a tree trunk is part of a larger community of organisms associated with this tree and including its subbark and trunk inhabitants, the population of the crown, rhizosphere, etc. In turn, this group is only one from the components of the forest biocenosis. The latter is part of more complex complexes that ultimately form the entire living cover of the Earth. Thus, the organization of life at the biocenotic level is hierarchical. 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 composition, functioning and development, that is, they are natural systems.

Discussing the general principles of the organization of life on Earth, the famous Russian biologist V.N. 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, poorly integrated, poorly organized, weakly closed. These are vague, not very defined, often difficult to catch collective formations, complexly intertwined with each other, imperceptibly transforming into each other and nevertheless quite real, existing and active, 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 develop 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.

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

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

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

3. 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. The interests of many species in the biocenosis are directly opposite. For example, predators are antagonists to their victims, but nevertheless they exist together, within a single community.

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

5. The maximum size of an organism is limited by its internal hereditary program. The dimensions of supraorganismal systems are determined by external factors. Thus, the biocenosis of white moss pine forest can occupy a small area among swamps, or it can extend over a considerable distance in an area with relatively homogeneous abiotic conditions.

These special principles of the formation of supraorganismal systems gave rise to a long discussion among ecologists, and primarily geobotanists, about the “continuity” and “discreteness” of the vegetation cover, which is the basis of terrestrial biocenoses (“continuum” - continuous, continuous, “discrete” - discontinuous). Proponents of the continuum concept pay primary attention to the gradual transition of 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 a plant community, the determining 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 are found together not because they have adapted to each other, but because they have adapted to a common environment. Any variation in habitat conditions causes changes in community composition.

The earlier concept of discreteness of phytocenoses, which was put forward by S. G. Korzhinsky at the beginning of the development of phytocenology, stated that the main thing in the organization of a plant community is the relationship between plants, i.e., internal factors. Its modern supporters, recognizing the existence of transitions between phytocenoses, believe that plant communities exist objectively, and are not a conditional selection from a continuous vegetation cover. They draw attention to the recurrence of the same combinations of species in similar conditions, the important environment-forming role of the most significant members of the phytocenosis, influencing the presence and distribution of other plants.

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

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.

There are 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.

There are species-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 sewage - wherever one or several environmental factors deviate far from the average optimal level for life, communities are greatly impoverished, since few species can adapt to such extreme conditions. The species spectrum is also small in those biocenoses that are often subject to some kind of catastrophic impacts, for example, annual flooding during river floods or regular destruction of plant cover during plowing, the use of herbicides and other anthropogenic interventions. Conversely, 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 regions, etc.

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 - 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. The agrocenosis of a wheat field, in addition to wheat, includes, at least in minimal quantities, various weeds, insect pests of wheat and predators that feed on phytophages, mouse-like rodents, invertebrates - inhabitants of the soil and 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 sludge, hydrogen sulfide springs, etc. . P.).

It is quite difficult to calculate the total number of species in a biocenosis due to methodological difficulties in recording microscopic organisms and the lack of development of taxonomy for 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 diverse relationships.

The complexity of the species composition of communities largely depends on the heterogeneity of the habitat. In such habitats, where species with 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 border, or edge, effect. It is well known that on the edges the vegetation is usually lush and richer, more species of birds nest, more species of insects, spiders, etc. are found 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 biotopes, the more heterogeneous the conditions at their boundaries and the stronger the border effect. Species richness increases greatly in places of contact between forest and herbaceous, aquatic and land 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). V.V. Alekhin (1882–1946) figuratively called the exceptional species richness of the flora of the European forest-steppe the “Kursk floristic anomaly.”

In addition to the number of species included in the biocenosis, 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 group in which 96 out of 100 individuals belong to one species and one individual each belongs to four others looks much more uniform than one in which all 5 species are represented equally - 20 individuals each.

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. So, for example, in soils the abundance of protozoa amounts to many tens of billions per square meter, nematodes - several millions, mites and springtails - tens or hundreds of thousands, earthworms - tens or hundreds of individuals. The number of burrowing vertebrates - mouse-like rodents, moles, shrews is no longer calculated per square meters, but per hectares of area.

Dimension species that make up natural biocenoses vary on a gigantic scale. For example, whales are 5 million times longer than bacteria and 3 × 10 20 in volume. Even within individual systematic groups, such differences are very large: if you compare, for example, giant trees and small grasses in the forest, tiny shrews and large mammals - elk, brown bear, etc. Different-sized groups of organisms live in biocenoses at different spatial scales 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. The living space of an insect such as a gall midge may be limited to 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 over hundreds and 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 sized worlds, and on the other hand, the closest connections are made in them precisely among organisms of different sizes.

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

Species of the same size class that are part of the same biocenosis vary greatly in abundance (Fig. 76). Some of them are rare, others are so common that they determine the appearance of the biocenosis, for example, feather grass in the feather grass steppe or wood sorrel in a spruce-sorrel forest. In each community, one can distinguish a group of main species, the most numerous in each size class, the connections between which, in essence, are decisive for the functioning of the biocenosis as a whole.

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, the kinglet, robin, and chiffchaff dominate the bird population, bank voles and red-gray voles dominate among mouse-like rodents, etc.

Dominants dominate the community and form the “species core” of any biocenosis (Fig. 77). Dominant, or mass, species determine its appearance, maintain the main connections, and have the greatest influence on the habitat. Typically, typical terrestrial biocenoses are named by their dominant plant species: pine-blueberry, birch-sedge, etc. Each of them is dominated by certain species of animals, fungi and microorganisms.

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. Species structure of the springtail community over 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, 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 (literal translation from Latin - builders) (Fig. 78). Removal of an edificator species from a 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 digging activity that mainly determines the nature of the landscape, the microclimate, and the growing conditions of plants. In the seas, 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 according to their abundance is characterized by the Raunkier curve (Fig. 79). A sharp rise in the left part of the curve indicates the predominance of small and rare species in the community, and a slight rise in the right part indicates the presence of a certain group of dominants, the “species core” of the community.

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

Rare and small species are also very important for the life of the biocenosis. 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., they give the biocenosis stability and ensure the reliability of its functioning in different conditions. The larger 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.

There is a certain connection between the number of dominant species and the overall 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 unhindered.

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 is called A. Tineman's rules, named after a German scientist who studied the features 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 observed in communities of very different sizes. In piles of fresh horse manure, for example, there is an almost anaerobic environment, a lot of ammonia and other toxic gases, high temperature due to the activity of microorganisms, i.e., sharply specific living conditions deviating from the usual norm are created for various animals. In such piles, the species composition of invertebrates is initially extremely poor. The larvae of fruit flies develop, and a few species of saprophagous nematodes (family Rhabditidae) and predatory gamasid mites (genus Parasitus) reproduce. But 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 part (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 cereal stems in the fields (according to N.I. Kulikov, 1988). On the x-axis are 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 small in number. In tropical forests it is rare to find several trees of the same species nearby. In such communities there are no outbreaks of mass reproduction of individual species; biocenoses are highly stable. A curve reflecting the species structure of this type would have in Fig. 76 especially steep left side.

Thus, even the most general analysis of the species structure can provide quite a lot for a holistic characterization of the community. The diversity of a biocenosis is closely related to its stability. Human activity greatly reduces diversity in natural communities. This makes it necessary to anticipate its consequences and take measures to maintain natural systems.

Quantitative characteristics of the species in the biocenosis. To assess the role of an individual species in the species structure of the biocenosis, various indicators based on quantitative accounting are used. Species abundance - this 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 in 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, projective abundance, or area coverage, is also taken into account. Frequency of occurrence characterizes the uniformity or unevenness of the distribution of the species in the biocenosis. It is calculated as the percentage of the number of samples or survey 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. A species may be numerous but low in occurrence or low in abundance 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 group under consideration. So, for example, if out of 200 birds recorded 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 in modern ecological literature, they often use diversity index calculated using Shannon's formula:

H = – ?P i log 2 P i,

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

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

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

When plants of different heights live together, the phytocenosis often acquires a clear tiered folding: Assimilating above-ground plant organs and their underground parts are located in several layers, using and changing the environment in different ways. Layering is especially noticeable in temperate forests. For example, in spruce forests the tree, herb-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, 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 (borets, spreading boron, forest chist, etc.); the fifth tier is made up of lower grasses (common grass, hairy sedge, perennial wood grass, etc.); in the sixth tier - the lowest grasses, such as European hoofed grass. Undergrowth of trees and shrubs can be of different ages and sizes and does not form special tiers. Tropical rainforests are the most multi-layered, while artificial forest plantations are the least dense (Fig. 81, 82).

In the forests there is always inter-tiered (extra-tiered) plants - these are algae and lichens on tree trunks and branches, higher spore and flowering epiphytes, lianas, etc.

Rice. 81. Multi-tiered tropical rain forest of the Central Amazon. Vegetation strip 20 m long and 5 m wide

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

Tiering allows plants to more fully use the light flux: shade-tolerant, even shade-loving, plants can exist under the canopy of tall plants, 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 layers than forests. However, sometimes in forests there are only two clearly defined tiers, for example in a white moss forest (woody, formed by pine, and ground - from lichens).

Rice. 83. Layered vegetation of the meadow steppe (according to V.V. Alekhin, A.A. Uranov, 1933)

Tiers are distinguished according to the bulk of the assimilating organs of plants, which have a great influence on the environment. Vegetation layers can be of different lengths: the tree layer, for example, is several meters thick, and the moss layer 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. For example, in a spruce forest, plants of the herbaceous-shrub layer (common wood sorrel, bileaf bileaf, blueberry, etc.) are in conditions of reduced lighting, equalized temperatures (lower during the day and higher at night), weak wind, high humidity and CO 2 content. Thus, the tree and herb-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 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 the following groups are distinguished: soil inhabitants - geobius, ground, surface layer – herpetobium, moss layer - bryobium, grass stand – phyllobium, higher tiers - Aerobic. Among the birds, there are species that nest only on the ground (chickens, grouse, pipits, buntings, etc.), others - in the bush layer (song thrushes, bullfinches, warblers) or in the crowns of trees (finches, kinglets, goldfinches, large predators, etc. .).

Dismemberment in the horizontal direction – mosaic - is characteristic of almost all phytocenoses, therefore, within their boundaries there are structural units that have received different names: microgroups, microcenoses, microphytocenoses, parcels, etc. These microgroups differ in species composition, quantitative ratio of different species, density, productivity and other properties.

The mosaic pattern is due to a number of reasons: heterogeneity of microrelief, soils, environment-forming influence of plants and their biological characteristics. 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. .

A. A. Uranov substantiated the concept of “phytogenic field”. This term denotes that area of ​​space that is affected by an individual plant, shading it, removing mineral salts, changing temperature and moisture distribution, supplying litter and metabolic products, etc. Individuals of different plant species have a different phytogenic field, which is manifested in spatial structure of phytocenoses.

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

Due to differences in the environment-forming activities of different plant species, individual areas in a spruce-broadleaf forest differ in many physical conditions (illumination, thickness of snow cover, amount of litter, etc.), so life in them proceeds differently: the grass stand, undergrowth, root growth are unequally developed systems of plants, small animals, etc.

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

Mosaicity, like layering, is dynamic: one microgrouping is replaced by another, growing or shrinking in size.

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

Species that perform the same functions in similar biocenoses are called vicarious (i.e. substituting). The phenomenon of ecological vicariate is widespread in nature. For example, a similar role is played by marten in the European taiga 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. A specific species for a biocenosis is to a certain extent a random phenomenon, since communities are formed from those species that exist in the environment. But the ecological structure of biocenoses that develop in certain climatic and landscape conditions is strictly natural. For example, in biocenoses of different natural zones the ratio of phytophages and saprophages naturally changes. In steppe, semi-desert and desert areas, phytophagous animals predominate over saprophagous animals; 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, while in the illuminated, surface zone of the pelagic there are many filter feeders that consume phytoplankton, or species with a mixed feeding pattern. 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 hygrophiles, mesophiles and xerophiles among animals, as well as the spectrum of life forms. 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, hygrophytes and even hydrophytes are more abundantly represented. 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 assessing biocenoses, which uses the general characteristics of its ecological, species and spatial structure, is called macroscopic. This is a generalized, large-scale characteristic of communities, which allows one to navigate the properties of the biocenosis when planning economic activities, predict the consequences of anthropogenic impacts, and 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 most subtle details of its ecology. This task has not yet been completed for the vast majority of species due to the extreme diversity of living forms in nature and the complexity of studying their ecological characteristics.

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.

Classifications of biocenotic relationships can be built using different principles. One popular approach is to assess the possible outcome of contacts between two individuals. For each of them, the result is accepted as positive, negative or neutral. Combinations of results for 2 out of 3 possible ones give a formal scheme of 6 options, which forms the basis for this classification.

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

Preying on prey requires them to expend significant energy on searching, chasing, capturing, and 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.

Foraging requires energy expenditure primarily in searching rather than capturing food. Such “gathering” is characteristic, for example, of a number of insectivorous birds - plovers, plovers, finches, pipits, etc. However, between typical predation and typical gathering, carnivores have many intermediate methods of obtaining food. For example, a number of insectivorous birds are characterized by hunting behavior when catching insects (swifts, swallows). Shrikes and flycatchers lie in wait and then overtake the prey like typical predators. On the other hand, the feeding method of carnivorous foragers is very similar to the collection of stationary food by herbivorous animals, for example, seed-eating birds or rodents (dove, rock pigeon, lentil, wood mouse, hamsters, etc.), which are also characterized by specialized search forms of behavior.

Gathering may include filtration feeding of aquatic animals, sedimentation, or sedimentation of water suspension, food collection by mud eaters or earthworms. It is also associated with the so-called plant predation. Many plants, with a lack of nitrogen in their diet, have developed methods for catching and fixing insects flying to them and digesting their body proteins with proteolytic enzymes (pemphigus, sundews, nepenthes, Venus flytrap, etc.).

In terms of the method of acquiring food objects, gathering approaches typical grazing phytophages. The specificity of grazing is the eating of stationary food, which is in relative abundance, the search for which does not require much effort. From an ecological point of view, this feeding method is typical both for a herd of ungulates in a meadow, and for leaf-eating caterpillars in the crown of a tree or ladybird larvae in aphid colonies.

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

Defensive adaptations among potential victims are very diverse, sometimes very complex and unexpected. For example, cuttlefish, escaping from a pursuing predator, empty their ink sac. According to hydrodynamic laws, the liquid thrown out of the bag by a fast-swimming animal does not spread out for some time, taking on the shape of a streamlined body, similar in size to the cuttlefish itself. Deceived by the dark outline that appears before its eyes, the predator “grabs” the ink liquid, the narcotic effect of which temporarily deprives it of the ability to orient itself in the environment. Pufferfish have a unique method of protection. Their shortened body is covered with adjacent spines. A large sac extending from the stomach allows these fish, in case of danger, to swell into a ball, swallowing water; at the same time, their needles straighten out and make the animal practically invulnerable to predators. An attempt by a large fish to grab a pufferfish can result in its death from a prickly ball stuck in its throat.

In turn, the difficulty of detecting and capturing prey contributes to selection among predators for better development of sensory organs (sightedness, keen hearing, sense of smell, etc.), a faster reaction to prey, endurance during pursuit, etc. Thus, ecological connections between predators and prey direct the course of evolution of related species.

Predators usually have a wide range of diets. Preying on victims requires a lot of strength and energy. Specialization would make predators highly dependent on the abundance of a particular type of prey. Therefore, most species leading a predatory lifestyle are able to switch from one prey to another, especially to the one that is more accessible and abundant at a given period. True, many predators have preferred types of prey, which they hunt more often than others. This selectivity may be due to various reasons. Firstly, the predator actively chooses the most nutritionally nutritious food. For example, diving ducks and whitefish in northern reservoirs choose mainly the larvae of chironomid mosquitoes (bloodworms) among aquatic invertebrates, 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 the food for which it is most adapted. Thus, many passerines feed on all insects that live openly on the surface of the soil, on grass, leaves, etc., but do not eat soil invertebrates, the extraction of which requires special devices. Finally, the third reason for the food selectivity of predators may be an active switch to the most abundant prey, the appearance of which stimulates hunting behavior. When the number of lemmings is high, even peregrine falcons, whose main method of hunting is catching birds in the air, begin to hunt lemmings, grabbing 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.

Commensalism - this is a form of relationship between two species when the activity of one of them provides food or shelter to the other (commensal). In other words, commensalism is the unilateral use of one species by another without causing harm to it. Commensalism, based on the consumption of food leftovers from the hosts, is also called freeloading. Such, for example, is the relationship between lions and hyenas, who pick up the remains of prey left uneaten by the lions. The commensals of large sharks are the sticky fish that accompany them, etc. A freeloading relationship is established even between insects and some plants. The liquid in the pitchers of insectivorous Nepenthes contains dragonfly larvae, protected from the digestive action of plant enzymes. They feed on insects that fall into trapping jars. Excrement consumers are also commensals of other species.

The use of shelters either in buildings or in the bodies of other species is especially developed. This commensalism is called Tenancy. Fieraster fish hide in the aquatic lungs of sea cucumbers, juveniles of other fish hide under the umbrellas of jellyfish protected by stinging threads. Commensalism is the settlement of epiphytic plants on the bark of trees. Bird nests and rodent burrows are home to a huge number of species of arthropods that use the microclimate of shelters and find food there from decaying organic remains or other types of cohabitants. Many species are specialized in this way of life and are not found outside their burrows at all. Permanent burrowing or nesting cohabitants are called Nidikolov.

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 develops 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 young ants, who groom them, lick them and transfer them to special chambers. Ants also feed adult beetles. However, the beetles and their larvae eat the eggs and larvae of their hosts without encountering resistance from them. 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, which extremely attracts ants. The secret contains ethers, which have a stupefying, narcotic effect on ants, similar to the effect of alcohol. Ants constantly lick Lomechus and Atemeles. As a result, their instincts are upset, coordination of movements is disrupted, and even some morphological changes appear. Working ants in colonies where there are many Lomechus are inactive and lethargic. Families become small and die as a result.

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

Intestinal symbionts involved in the processing of rough plant feed are found in many animals: ruminants, rodents, borer beetles, chafer 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. It is known that many species of trees coexist with mycorrhizal fungi, and leguminous plants with rhizobium nodule bacteria, which fix molecular nitrogen in the air. Nitrogen-fixing symbionts have been 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 squids - sacs filled with luminous bacteria and part of the luminescent organs - photophores.

The line between symbiosis and other types of relationships is sometimes very arbitrary. It is interesting that lagomorphs and some rodents use their intestinal microflora. Rabbits, hares, and pikas have been found to regularly eat their own feces. Rabbits produce two types of excrement: dry and soft, mucous-coated. They lick soft feces directly from the anus and swallow without chewing. Research has shown that such coprophagia is quite natural. Rabbits deprived of the opportunity to consume soft feces lose weight or gain poor 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 lagomorphs is a fermentation tank for the processing of fiber and is saturated with symbiotic microorganisms. In 1 g of soft feces there are up to 10 billion bacteria. When microorganisms enter the rabbit's stomach along with feces, they are completely killed by acid and are digested in the stomach and long small intestine. Thus, in exclusively herbivorous lagomorphs, coprophagy is a way of obtaining essential amino acids.

Less obligatory, but extremely significant, are the mutualistic relationships between the Siberian pine pine and the birds nesting in cedar forests - the nutcracker, nuthatch and jock. 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. 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 seeds cannot germinate on a thick layer of forest litter that blocks their access to the soil.

The relationship between plants that have succulent fruits and birds that feed on these fruits and distribute seeds that are usually indigestible is mutually beneficial. Mutualistic relationships with ants develop in many plants: about 3,000 species are known that have adaptations for attracting ants. A typical example is cecropia, a tree found in the Amazon. Ants of the genera Azteca and Cramatogaster inhabit voids in the articulated trunk of cecropia and feed on special round formations with a diameter of about 1 mm - “Müllerian bodies”, which the plant produces on swellings located on the outer side of the leaf sheath. Cohabiting ants vigilantly protect leaves from pests, especially leaf-cutter ants of the genus Atta.

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

Neutralism - this is a form of biotic relationships in which the cohabitation of two species in the same territory does not entail either positive or negative consequences for them. With neutralism, 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, have virtually no contact with each other. However, suppression of the forest by prolonged drought or its denudation due to the mass proliferation of pests affects each of these species, although to a different extent. Relations of the neutralism type are especially developed in species-rich communities that include 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 tree experience oppression 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 and influence the distribution and mutual selection of species.

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 opportunity to acquire food, shelter and other means of subsistence available in the habitat. Competition is the only form of environmental relations that negatively affects both interacting partners.

Forms of competitive interaction can be very different: from direct physical struggle to peaceful coexistence. However, if two species with the same ecological needs end up in the same community, sooner or later one competitor will displace the other. This is one of the most general environmental rules, which is called competitive exclusion law and was formulated by G.F. 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 one of the most important components of the struggle for existence, playing a large role in the evolution of species.

In G. F. Gause's experiments with cultures of Paramecium aurelia and P. caudatum slippers, each species, placed separately in test tubes with hay infusion, successfully multiplied, reaching a certain level of abundance. If both species with a similar feeding pattern were placed together, then at first an increase in the number of each of them was observed, 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. Increase in the number of ciliates Paramaecium caudatum (1) and P. aurelia (2) (according to G.F. Gause from F. Dre, 1976): A – in a mixed culture; B – in separate cultures

The winner in the competition is, as a rule, the species that in a given ecological situation has at least slight advantages over another, i.e., is more adapted to environmental conditions, since even closely related species never coincide across the entire ecological spectrum. Thus, 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 takes place. In numerous cups with flour, in which several specimens of beetles of two species (Tribolium confusum and T. castaneum) were placed and in which they multiplied, after some time 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 the factors, the “victory” of one type or another was clearly of a random nature, and it was difficult to predict the outcome of the competition.

The reasons for the displacement of one species by another may be different. Since the ecological spectra of even closely related species never completely coincide, despite the general similarity of environmental requirements, species still differ from each other in some way. Even if such species live peacefully together, but the reproduction intensity of one is slightly greater 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 canopy of leaves early, but is then shaded by T. fragiferum, which has longer petioles. When duckweeds Lemna gibba and Spirodela polyrrhiza are grown together, the number of the second species first increases and then decreases, although in pure cultures the growth rate of this species is higher than that of the first. The advantage of L. gibba in this case is that under thickening conditions it develops aerenchyma, which helps it float on the surface of the water. S. polyrrhiza, which does not have aerenchyma, is pushed down and shaded by a competitor.

The chemical interactions of plants through the products of their metabolism are called allelopathy. Animals also have similar ways of influencing each other. In the above experiments by G. F. Gause and T. Park, the suppression of competitors occurred mainly as a result of the accumulation in the environment of toxic metabolic products, to which one of the species is more sensitive than the other. Higher plants with a low nitrogen requirement, which are 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 secretions. By preventing the enrichment of the soil with nitrogen, they gain advantages in competition with plants that require large amounts of it in the soil. Cattail in overgrown reservoirs is allelopathically active in relation to other aquatic plants, which allows it, avoiding competitors, to grow in almost pure thickets.

In animals, there may be cases of direct attack by one species on another in competition. For example, the larvae of the egg eaters Diachasoma tryoni and Opius humilis, which find themselves in the same host egg, fight with each other and kill the opponent before starting to feed.

The possibility of competitive displacement of one species by another is the result ecological individuality of species. Under constant conditions, they will have different competitiveness, since they necessarily differ from each other in tolerance to some factors. In nature, however, in most cases the environment is variable both in space and time, and this makes it possible for many competitors to coexist. For example, if weather conditions change more or less regularly in favor of one species or another, the beginning processes of displacing each other do not reach completion and change sign to the opposite. Thus, in wet years, mosses can grow in the lower layer of the forest, and in dry years they are crowded out by a cover of hairy sedge or other grasses. These species also coexist in the same phytocenosis, occupying forest areas with different moisture conditions. In addition, species that compete for more than one resource often have different thresholds of limiting factors, which also prevents the processes of competitive exclusion from completing. Thus, the American ecologist D. Tillman, cultivating two types of diatoms together, found out that they do not displace each other because they have different sensitivity to the lack of nitrogen and silicon. A species that is capable of reproducing ahead of another with 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 coexist in a 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, a predator, a starfish, which fed mainly on mussels, was removed from the bottom of a coastal area of ​​the sea, where 8 species of sessile invertebrates lived - mussels, sea acorns, sea ducks, chitons. After some time, mussels occupied the entire area of ​​the bottom, displacing all other species.

Thus, biocenoses contain in each group of organisms a significant number of potential or partial competitors that are in dynamic relationships with each other. A species may also have no strong competitors, but may be slightly influenced by each of the many others that share its resources. In this case they talk about "diffuse" competition, the outcome of which also depends on many circumstances and may result in 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 released when the activities of neighbors weaken and replace them in biocenotic connections, which preserves and stabilizes the biocenosis as a whole.

As with all other forms of biotic relationships, competition is often not easily separated from other types of relationships. In this regard, the behavioral features of ecologically similar ant species are indicative.

Large meadow ants Formica pratensis build mounded nests and guard the territory around them. In 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 feeding areas.

When experimentally isolating meadow ant nests, the hunting efficiency of F. cunicularia increases 2–3 times. The ants bring larger insects, which are usually prey for F. pratensis. If F. cunicularia nests are isolated, the prey of meadow ants does not increase, as would be expected, but is reduced by half. It turned out that the more mobile and active foragers of F. cunicularia serve as stimulators of the search activity of meadow ants, as a kind of scouts for protein food. The intensity of movement of meadow ant foragers along roads in those sectors where there are F. cunicularia nests is 2 times higher than in those areas where there are none. Thus, the overlap of the hunting territory and food spectra allows us to consider F. cunicularia as a competitor of meadow ants, but the increased hunting efficiency of F. pratensis indicates the benefit of F. cunicularia staying on their territory.

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

Mutualistic and competitive relationships represent the basic 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 types of biotic connections cannot fully reflect all their diversity and complexity in living nature, but still allows one to navigate the main types of interaction between organisms. Other classifications focus on other aspects of biotic relationships using different approaches.

V.N. Beklemishev divided the relationships between species in a community into direct and indirect. Direct connections occur through direct contact between organisms. Indirect connections represent the influence of species on each other through their habitat or by influencing third species.

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

Trophic connections arise when one species feeds on another - either living individuals, or their dead remains, or waste products. And dragonflies, which catch other insects in flight, and dung beetles, which feed on the droppings of large ungulates, and bees, which collect nectar from plants, enter into a direct trophic relationship with the species that provide them with food. In the case of competition between two species over food items, an indirect trophic relationship arises between them, since the activity of one is reflected in 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.

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

Rice. 88. Herring food connections – part of the ocean food web

Any biocenosis is permeated with food connections and represents a more or less spatially localized section of the general trophic network that connects all life on Earth.

Individual consortia may vary in complexity. The plants that play the main role in creating the internal environment of the biocenosis have the largest number of consort relations. 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 relations, which are based on topical relationships, form a kind of block structure of the biocenosis.

Topical and trophic connections are of greatest importance in a biocenosis and 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.

Phoric connections is the participation of one species in the spread of another. Animals act as transporters. The transfer of seeds, spores, and pollen by animals is called zoochory, transfer of other, smaller animals – phoresia (from lat. foras- out, out). Transfer is usually carried out using special and various devices. Animals can capture plant seeds in two ways: passive and active. Passive capture occurs when the body of an animal accidentally comes into contact with a plant, the seeds or infructescences of which have special hooks, hooks, and outgrowths (seed, burdock). Their distributors are usually mammals, which carry such fruits on their fur, sometimes over quite considerable distances. The active method of capture is eating fruits and berries. Animals excrete seeds that cannot be digested along with their droppings. Insects play an important role in the transmission of fungal spores. Apparently, the fruiting bodies of fungi arose as formations that attracted insect dispersers.

Rice. 89. Phoresia of mites on insects:

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

2 – phoresia of mites on ants

Animal phoresia is widespread mainly among small arthropods, especially in various groups of mites (Fig. 89). 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. For example, many flying insects - visitors to accumulations of rapidly decomposing plant remains (animal corpses, ungulate droppings, heaps of rotting plants, etc.) carry gamasid, uropod or thyroglyphoid mites, which thus move from one accumulation of food materials to another. Their own dispersal capabilities do not allow these species to travel significant distances. Dung beetles sometimes crawl with raised elytra, which they are unable to fold due to mites densely littering their bodies. Some types of nematodes spread to insects through phoresy (Fig. 90). The legs of dung flies often have a lampbrush appearance due to the abundance of nematodrabditids attached to them. Among large animals, phoresia is almost never found.

Rice. 90. Dispersal of nematode larvae on beetles:

1 – larvae waiting for a settler;

2 - larvae attached under the elytra of the beetle

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 structures (fabrications). Thus, birds use tree branches, mammal fur, grass, leaves, down and feathers of other bird species, etc. to build nests. Caddisfly larvae build houses from pieces of branches, bark or leaves of plants, from the shells of small types of coils, even capturing shells with live shellfish. The megachila bee places eggs and supplies in cups constructed from the soft leaves of various shrubs (rose hips, lilac, acacia, etc.).

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

1 – physiological optimum curves;

2 – synecological optimum (according to V. Larcher, 1978)

7.4. Ecological niche

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

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

The concept of “ecological niche” should be distinguished from the concept of “habitat”. In the latter case, we mean 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 abiotic environmental conditions, but also, no less, on its biocenotic environment. The nature of the ecological niche occupied is determined both by the ecological capabilities of the species and by the extent to which these capabilities can be realized in specific biocenoses. This is a characteristic of the lifestyle that a species can lead in a given community.

G. Hutchinson put forward the concepts of a fundamental and realized ecological niche. Under fundamental refers to the entire set of conditions under which a species can successfully exist and reproduce. In natural biocenoses, however, species do not develop 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 capabilities of a species, and the realized one characterizes that part of them that can be realized under given conditions, given the availability of the resource. Thus, the realized niche is always smaller than the fundamental one.

In ecology, the question of how many ecological niches a biocenosis can accommodate and how many species of any particular group that have similar environmental requirements can live together is widely discussed.

Specialization of a species in nutrition, use of space, time of activity and other conditions is characterized as a narrowing of its ecological niche, while reverse processes are characterized as its expansion. The expansion or narrowing of the ecological niche of a species in a community is greatly influenced by competitors. Competitive exclusion rule formulated by G.F. Gause for species that are similar in ecology, can be expressed in such a way that two species do not coexist in the same ecological niche.

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

Exit from competition is achieved due to divergence of requirements for the environment, changes in lifestyle, which, in other words, is the delimitation of the ecological niches of species. In this case, they acquire the ability to coexist in the same biocenosis. Each of the species living together is capable of more complete use of resources in the absence of a competitor. This phenomenon is easy to observe in nature. Thus, herbaceous plants in a spruce forest are able to be content with a small amount of soil nitrogen, which remains from being intercepted by tree roots. However, if the roots of these spruce trees are cut off in a limited area, the nitrogen nutrition conditions for the grasses improve and they grow rapidly, taking on a dense green color. Improving living conditions and increasing the number of a species as a result of removing from the biocenosis another, similar in environmental requirements, is called competitive release.

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

Closely related species living together usually have very fine delineations of ecological niches. Thus, ungulates grazing in African savannas use pasture food in different ways: zebras pluck mainly the tops of grasses, wildebeests feed on what zebras leave for them, choosing certain types of plants, gazelles pluck the shortest grasses, and topi antelopes are content with tall dry ones. stems left behind by other herbivores. The same “division of labor” in the southern European steppes was once carried out by wild horses, marmots and gophers (Fig. 92).

Rice. 92. Different types of herbivores eat grass at different heights in African savannas (top rows) and in the Eurasian steppes (bottom rows) (according to F. R. Fuente, 1972; B. D. Abaturov, G. V. Kuznetsov, 1973)

In our winter forests, insectivorous tree-feeding birds also avoid competition with each other due to their different search patterns. For example, nuthatches and pikas collect food on tree trunks. At the same time, nuthatches quickly examine the tree, quickly grabbing insects or seeds caught in large cracks in the bark, while small pikas carefully search the surface of the trunk for the smallest cracks into which their thin awl-shaped beak penetrates. In winter, in mixed flocks, great tits conduct a wide search in trees, bushes, stumps, and often in the snow; Chickadees inspect mainly large branches; long-tailed tits search for food at the ends of branches; small kinglets carefully search the upper parts of coniferous crowns.

Ants exist in natural conditions in multi-species associations, the members of which differ in lifestyle. 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 litter, the ground layer is colonized by L. niger and F. fusca, trees – Camponotus herculeanus. Specialization for life in different tiers is reflected in the life form of species. In addition to separation in space, ants also differ in the nature of obtaining food and in the time of daily activity.

In deserts, the most developed complex of ants collect food on the soil surface (herpetobionts). Among them, representatives of three trophic groups stand out: 1) diurnal zoonecrophages - active in the hottest time, feeding on the corpses of insects and small living insects 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) - eat plant seeds.

Several species from the same trophic group can live together. The mechanisms for exiting competition and delineating ecological niches are as follows.

1. Size differentiation (Fig. 93). For example, the average weights of working individuals of the three most common diurnal zoonecrophages in the Kyzylkum sands are in the ratio 1:8:120. Approximately the same ratio of weights is found in a medium-sized cat, lynx and tiger.

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

2. Behavioral differences consist of different foraging strategies. Ants that create roads and use the mobilization of carriers to carry discovered food to the nest feed primarily on the seeds of plants that form clumps. Ants, whose foragers work as solitary foragers, collect mainly seeds of plants that are dispersedly distributed.

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

4. Differences in activity times relate mainly to the time of day, but in some species there are discrepancies in activity between seasons (mainly spring or autumn activity).

The ecological niches of species vary 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 May beetles, 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 are part of different food chains. The fry live off small plankton, while the adults are typical predators.

The weakening of interspecific competition leads to the expansion of the ecological niche of the species. On oceanic islands with a poor fauna, a number of birds, compared to their relatives on the mainland, inhabit more diverse habitats and expand the range of food, since they do not encounter competing species. Among island inhabitants, there is even 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 the manifestation of all its potential, then intraspecific competition, on the contrary, contributes to the expansion of ecological niches. With an increased number of species, the use of additional food begins, the development of new habitats, and the emergence of new biocenotic connections.

In reservoirs, plants that are completely immersed in water (elodea, hornwort, urut) find themselves in different conditions of temperature, illumination, and gas conditions than those floating on the surface (telores, watercolor, duckweed) or rooting at the bottom and bringing 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). Different epiphytic orchids have highly specialized pollinators.

In a mature broad-leaved forest, the trees of the first tier - common oak, smooth elm, sycamore maple, heart-leaved linden, and common ash - have similar life forms. The tree canopy formed by their crowns ends up in the same horizon, under similar environmental conditions. But a careful 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 and shade tolerance, timing of flowering and fruiting, methods of pollination and distribution of fruits, composition of consorts, etc. Oak, elm and ash are anemophilous plants, but the saturation of the environment with their pollen occurs at different times. Maple and linden are entomophiles, good honey plants, but they bloom at different times. Oak has zoochory, while other broad-leaved trees have anemochory. The composition of consorts is different for everyone.

If in a broad-leaved forest the tree crowns are located in the same horizon, then the active root endings are located at different depths. The roots of oak penetrate most deeply, the roots of maple are located higher and the roots of ash are even more superficial. The litter of different tree species is utilized at different rates. The leaves of linden, maple, elm, and ash almost completely decompose by spring, and the leaves of oak still form loose forest litter in the spring.

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

During ontogenesis, plants, like many animals, change their ecological niche. As they age, they use and transform their environment more intensively. The transition of a plant into the generative period significantly expands the range of consorts and changes the size and intensity of the phytogenic field. The environment-forming role of aging, senile plants decreases. They are losing many consorts, but the role of the destructors associated with them is increasing. Production processes are weakened.

Plants have overlapping ecological niches. It intensifies 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 foliage layer diversity and bird species diversity (Shannon MacArthur indices from E. Pianka, 1981)

7.5. Coenotic strategies of species

In phytocenology, classifications of plants have been developed according to their ability to grow together and their coenotic significance. The general provisions of these classifications can also be applied to animals, since they characterize a kind of species strategy that determines 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 phytocenotypes. L. G. Ramensky proposed to distinguish between three types of plants living together - violents, patients and explerents. He popularly characterized them as enforcers, endurance and performers (i.e., space fillers), likening them to lions, camels and jackals. Violents have a high competitive ability in these conditions: “developing energetically, they seize territory and retain it, suppressing, drowning out rivals with vital energy and complete use of environmental resources.” Patients “in the struggle for existence... they are taken 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 violents. Explerents “they have a very low competitive power, but they are able to very quickly capture vacated territories, filling the gaps between strong plants, and they are just as easily replaced by the latter.”

More detailed classifications also identify other intermediate types. In particular, one can also distinguish a group pioneer species that quickly occupy newly emerging areas where there was no vegetation yet. Pioneer species partially have the properties of explorers - low competitive ability, but, like patients, they have high tolerance to the physical conditions of the environment.

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

In almost any group of organisms, species similar in their ability to coexist are distinguished, therefore the Ramensky-Grime classification of coenotic strategies can be classified as general ecological.