The concept of biocenosis. Structure of biocenosis. Structures and connections of the biocenosis Spatial structuring of the community
The term “biocenosis” was first used in his work by Karl Mobius in 1877 to describe all organisms inhabiting an area and interacting with each other. He combined the Greek words “βίος” - life and “κοινός” - general into one, which formed the basis of the concepts “spatial structure of biocenosis” and many others.
Animals, vegetation and microorganisms, in all their diversity, living and growing in a certain territory, designated by conventional boundaries, are called biocenosis. In addition, all living things are influenced by the environment, that is, the organic interacts with the inorganic. And this is happening and has been happening for a long period of time.
Even an inattentive observer will notice that animals and plants, microorganisms, are widespread or distributed across the territory they occupy, in width and height. This distribution is called spatial.
In addition, all living organisms existing in this area have species diversity. All these species together or their totality constitute the species structure of the biocenosis.
During growth, the grain consumes useful substances from the ground, and they are obtained when the worms “recycle” all the previous ones after their death. The worm is eaten by a bird. And so on in a circle. This cycle is the trophic structure of the biocenosis. A cat, a mouse, a bird, a grain and others are links, and all together trophic chain.
Thus, the ecological structure of the biocenosis has three types.
The structure characterizing its spatial content is divided into two types.
Height distribution is a vertical or tiered structure. Distribution in width or plane - horizontal or mosaic.
Tiers are most clearly expressed in plants and represent their species distribution across layers located at different distances from the ground. Based on this characteristic, plants are divided into shade-tolerant and light-loving. If we list from the ground up, then there are moss-lichen, shrub-herbaceous, shrub and tree layers.
We can talk about tiers of habitat in insects. Here the principle of distribution of species is as follows: inhabitants of the soil, its surface layer, mosses, grass, and the last one - the topmost one.
For animals and birds, tiers are practically not expressed.
The horizontal structure, that is, a planar cut at each of the vertical levels, is characterized by species diversity or mosaic. The occupancy rate of each such layer with living organisms depends on several factors. This is the influence of the surrounding inanimate nature or an abiogenic factor. Vegetation of this horizon. The combined influence of inanimate nature and flora. And the last factor inherent at the soil level is the diversity that arose as a result of the activity of burrowing animals.
The species structure of the biocenosis, that is, the totality of all types of flora and fauna, is formed depending on various factors. There are communities with a predominance of animal species, and others with plant species. And the totality of species itself can change. The most famous such change can be considered a decrease in species diversity from topical zones to the Earth's poles. As we approach the “tops” of the planet, the number of species, both plants and animals, decreases.
A prime example is the diversity of species in rain forests. For example, in the Amazon River basin they can only be counted in trees up to 90 per 1 hectare. While in temperate latitudes, the same trees will have no more than 10. At the junction of the taiga and tundra zones there will be a maximum of 5. And there will be no trees at all in the Arctic zone or alpine highlands. The picture is the same in the world of animals and microorganisms.
This structure is characterized not only by the number of species, but also by the number of individuals in each species. This indicates the richness of the biocenosis and is its qualitative characteristic. The species that has the largest number of individuals, has the greatest biomass or productivity is called dominant or dominant. This is especially clearly illustrated by a spruce forest, where trees of this species fill the entire area and shade, preventing other vegetation from developing.
Competition that arises between two species leads to the displacement of one by the other from the habitat. Based on the results of his observations and research, this principle of competitive exclusion was formulated by G.F. Gause.
Trophic
The trophic structure is based on three groups of organisms.
The first is producers, that is, those who produce. These are organisms that produce or synthesize organic substances from water and carbon dioxide, that is, from inorganic substances. They use solar energy as a source. The term “producer” usually refers to green plants, which make up about 99% of all life on Earth. Green plants are the basis of the ecological pyramid and its first link.
The third group is decomposers or reducers. These include organisms that break down dead organic matter and convert it into inorganic matter. In the food chain given earlier, they were worms. In addition to them, protozoa, fungi, bacteria and other microorganisms are decomposers. As a result of their activity, organic residues are converted into CO2, H2O and simple salts. This ends the trophic chain and begins again.
In a biocenosis, trophic connections between producers, consumers and decomposers must be constant and uninterrupted. If they rupture or at least slow down or pause in time, this may lead to the death of the entire biocenosis.
Peculiarities
Any of the described structures is not stable and unchangeable. Their boundaries are conditional. Living organisms from one tier or horizontal section can flow or influence another. Starting life on one level and ending it on another. An example would be insects, whose larvae develop in water or soil, and themselves live and die in the upper tiers.
The ecological structure of the biocenosis stands somewhat apart, because it is based on the principle of adaptation of species to various circumstances. For example, to nutrition, appearance, environment, size and so on. The peculiarity is that these circumstances or conditions can be natural, or they can be created and shaped by man. The presence of natural and artificial factors determines the number and quality of species occupying a certain territory or ecological niche.
An inorganic or nonliving environment that forms a homogeneous space for living organisms is called a biotope, the dimensions of which can be very different. The ecological type of biocenosis is considered in inextricable connection with the biotope.
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Biocenosis structure
There are species, spatial and ecological structures of the biocenosis.
Species structure – the number of species forming a given biocenosis and the ratio of their numbers or mass. That is, the species structure of the biocenosis is determined by species diversity and the quantitative ratio of the number of species or their mass to each other.
Species diversity – number of species in a given community. There are species-poor and species-rich biocenoses. Species diversity depends on the age of the community (young communities are poorer than mature ones) and on the favorableness of the main environmental factors - temperature, humidity, food resources (biocenoses of high latitudes, deserts and highlands are poor in species).
R. Whittaker proposed to distinguish the following types of biodiversity: α -diversity – species diversity in a given habitat; β -diversity – the sum of all species of all habitats in a given area; γ- diversity– diversity of landscapes (combination of α- and β- diversity).
Jaccard's laws of diversity – 1) species diversity of a territory (γ-diversity) is directly proportional to its diversity environmental conditions; 2) the species richness of the community (α-diversity) increases simultaneously with the expansion of the area and decreases as the homogeneity of the latter increases.
De Candolle-Wallace's Rule for Geographical Determination of Diversity Changes – as you move from north to south, as a rule, there is an increase in the species diversity of communities.
Darlington's rule – reducing the area of the island by 10 times, as a rule, reduces the number of animals living on it by half.
Distinguishes between 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. The species spectrum is also small in those biocenoses that are often subject to some catastrophic impacts, for example, annual flooding due to river floods or regular destruction vegetation 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, vegetable gardens) are also poorer in species than similar ones natural systems(forest steppe, meadow).
However, even the most impoverished biocenoses include, according to at least hundreds of species of organisms belonging to different systematic and ecological groups. In the agrocenosis of a wheat field, in addition to wheat, they include at least minimum quantity, 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, pathogenic fungi and many others. Species-rich natural communities include thousands and even tens of thousands of species, united by a complex system of diverse relationships.
They are distinguished by high species diversity ecotones – transition zones between communities, and the increase in species diversity here is called edge effect. It is well known that the vegetation on the edges is usually lush and richer, nesting more types birds, there are more species of insects, spiders, etc. than in the depths of the forest. Here the conditions of illumination, humidity, and temperature are more varied (forest-tundra, forest-steppe).
The importance of an individual species in the species structure of the biocenosis is judged by several indicators: species abundance, frequency of occurrence and degree of dominance. Abundance of the species - the number or mass of individuals of a given species per unit area or volume of space occupied by it. Frequency of occurrence – percentage of the number of samples or survey sites where the species occurs, to total number samples or recording sites. Characterizes the uniformity or unevenness of the distribution of the species in the biocenosis. Degree of dominance – the ratio of the number of individuals of a given species to the total number of all individuals of the group under consideration. Diversity Index calculated by Shannon's formula H=‑Σ pi log2 pi, where Σ is the sign of the sum, pi – the share of each species in communities (by number or mass), and log2 pi– binary logarithm.
The community distinguishes the following types: dominant , predominant in numbers, and "minor" few and rare. Among the dominants, they especially highlight edifiers (builders) are species that determine the microenvironment (microclimate) of the entire community. As a rule, these are plants.
Dominants dominate the community and constitute the “species core” of any biocenosis. 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.
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 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. They 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.
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.
RuleTieneman – The more specific the environmental conditions, the poorer the species composition of the community and the higher the number of individual species can be. 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.
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 and biocenoses are highly stable.
Spatial structure – distribution of organisms different types in space (vertically and horizontally). The spatial structure is formed primarily by the plant part of the biocenosis. Distinguish tiering (vertical structure of biocenosis) and mosaic (horizontal structure of the biocenosis).
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.
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.
Layering is also expressed in herbaceous communities (meadows, steppes, savannas), but not always clearly enough.
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.
Ecological structure – ratio of different organisms environmental groups. Biocenoses with a similar ecological structure may have different species composition. This is due to the fact that the same ecological niches can be occupied by species that are similar in ecology, but are far from related. These types are called replacing or vicarious .
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 hygro- and even hydrophytes are more abundant.
Important characteristics of the structure of a biocenosis are consortium, synusia and parcel. Consortium – a structural unit of a biocenosis that unites autotrophic and heterotrophic organisms on the basis of spatial (topical) and food (trophic) connections around a central member (core). For example, a single tree or group of trees (edificator plant) and associated organisms. A biocenosis is a system of interconnected consortia.
Sinusia – a structural part in the vertical division of a biocenosis, formed by species similar in life form and limited in space (or time). Spatially, a synusia can coincide with a horizon, canopy, layer, or tier of a biogeocenosis. For example, in a pine forest one can distinguish pine synusia, lingonberry synusia, green moss synusia, etc.
Parcel – a structural part in the horizontal division of a biocenosis, differing from other parts in the composition and properties of the components. The parcel is isolated (limited) by the leading element of vegetation. For example, areas of broad-leaved trees in a coniferous forest.
Lecture No. 5
(for the bachelor's degree "Standardization and Metrology"
Topic: “Ecological communities and ecosystems. Biocenosis. Biogeocenosis".
1. The concept of biocenosis
2. Species structure of the biocenosis
3. Spatial structure of the biocenosis
4. Relationships of organisms in biocenoses
5. Ecological niches
6. Ecological structure of the biocenosis
7. Border effect
The concept of biocenosis
Populations of different species in natural conditions unite into systems of a higher rank - communities and biocenosis. From lat. bios - life, cenosis – general.
The term “biocenosis” was proposed by the German zoologist K. Moebius.
Biocenosis is a collection of populations of all types of living organisms inhabiting a certain geographical territory that differs from other neighboring territories in terms of chemical composition soils, waters, as well as a number of physical indicators (altitude above sea level, solar radiation, etc.)
The composition of the biocenosis includes: plant and animal components, a component of microorganisms.
Specific communities develop under strictly defined environmental conditions. Interacting with components of the biocenosis such as plants and microorganisms, soil and groundwater form edaphotope, and the atmosphere is climate control
Components related to inanimate nature form ecotop. A space occupied by a biocenosis that is relatively homogeneous in terms of abiotic environmental factors is called biotope.
The part of ecology that studies the composition of communities and the joint life of organisms in them is called synecology.
The biocenosis and the biotope have a mutual influence on each other, expressed mainly in the continuous exchange of energy.
Small communities are part of larger ones, and those in turn are parts of even larger communities.
Species structure of the biocenosis.
The species structure of a biocenosis is understood as the diversity of species in it and the ratio of their numbers or mass.
Each specific biocenosis is characterized by a strictly defined species composition.
Young, just emerging biocenoses have a smaller set of species than long-established ones.
Biocenoses created by humans (gardens, vegetable gardens, fields) are usually poorer in species compared to similar natural systems (forests, meadows, steppes).
To assess the role of an individual species in the species structure of the biocenosis, indicators based on quantitative accounting are used. This is the abundance of the species, the frequency of occurrence of the species, the constancy of the species.
Species abundance is the number of individuals of a given species per unit area or volume of occupied space.
Frequency of occurrence. Characterizes the uniformity or unevenness of the distribution of the species in the biocenosis. This indicator is calculated as a percentage of the number of samples where it occurs this type to the total number of samples.
Constancy. This indicator is the ratio of the number of samples R containing a given species multiplied by the total number of samples R and divided by the total number of samples. C = r. P expressed in %.
Depending on the value WITH The following categories of species constancy are distinguished:
- permanent species found in more than 50% of samples
- additional species found in 25-5% of samples
- random species occurring in less than 25% of samples
In a biocenosis that consists of several species, one or two species occupy the main area or volume. These species are called dominant or dominant. Terrestrial biocenoses, as a rule, are named after the dominant species, for example, birch forest, feather grass steppe, and so on.
Dominance degree is the ratio of the number of individuals of a given species to the number of individuals of all species of a given biocenosis.
So, if out of 200 birds recorded in a given territory, 100 are finches, then the degree of dominance of this species is 50%.
Species that live off dominants are called predominants. For example, in a pine forest, the dominant species are insects, squirrels, and mouse-like rodents that feed on pine.
In every biocenosis there are species that, through their vital activity, create an environment for the entire community and without which the existence of most other species is impossible. These types are called edifiers. Removing an edificator species from a biocenosis leads to a change in the microclimate of the entire biotope of this biocenosis.
The edifiers of terrestrial biocenoses are certain plant species: in birch forests - birch, in pine forests - pine
In addition to a relatively small number of dominant species, the biocenosis also includes small species and even rare forms. There is a certain connection between the number of dominant species and the overall species composition of the community. Close groups are formed within the biocenosis, depending on edificatory plants or other elements of the biocenosis, which are called consortia.
Consortiums- this is a set of populations of organisms whose vital activity within the same biocenosis is professionally or topically related to the central species - an autotrophic plant.
The role of the central species is played by the edificator plant, which determines the characteristics of the biocenosis. Populations of the remaining species of the consortium form its core, due to which there are species that destroy the organic matter created by autotrophs.
The population of an autotrophic plant on the basis of which a consortium is formed is called determinite, and the species united around it are called consorts.
Consorts are connected with the determinant trophically, that is, by food connections, or topically, that is, they find a home or shelter on it.
For example, insects that feed on the leaves of a tree are related to it trophically, and birds that eat these insects and live on these trees are related toptically.
In this regard, all consorts consist of consorts 1, 2 and so on in order.
The composition of the consortium is the result of a long process of selecting species capable of existing in the determinant habitat conditions. Each consortium represents a special structural unit of the biocenosis.
Spatial structure of the biocenosis. – is determined primarily by the composition of its plant part - phytocenosis, and the distribution of above-ground and underground plant masses.
In the course of long evolutionary development, adapting to certain abiotic and biotic conditions, living organisms found their place in the biocenosis. In most cases, this distribution is tiered.
Tiering is the vertical stratification of biocenoses into equally high structural parts. The layering is especially clearly visible in phytocenoses (plant communities).
A phytocenosis acquires a tiered character when it contains plants that differ in height. For example, forest, vertical structure.
Plants of each tier create their own microclimate and a specific habitat for specific animals, which form their own community in each tier. For example, bird species such as chickens or grouse nest only on the ground (in the ground layer), blackbirds, bullfinches - in the bush layer, finches, goldfinches - in the crowns of trees, etc.
In biocenoses, the vertical distribution of organisms also determines a certain structure in the horizontal direction. The dismemberment of the biocenosis in the horizontal direction is called mosaic and is characteristic of almost all phytocenoses.
The mosaic pattern is due to such reasons as the heterogeneity of the microrelief, the biological characteristics of plants, the diversity of soil fertility, human activities (deforestation, mining, etc.) and the influence of the animal world (trampling meadows with hooves, etc.)
Interspecific relationships in the biocenosis according to the classification of V.N. Beklemishev are divided into four types: trophic, topical, phoric, factory. So:
1. Trophic connections- these are such connections when one species feeds on another: either living individuals, or their dead remains, or the products of their vital activity. When two species compete over food, an indirect trophic relationship arises between them, since the activity of one species affects the food supply of the other.
2. Topical connections– these are connections when changes in the living conditions of one species occur as a result of the life activity of another. This type of connection is very diverse. Topical connections consist in the creation of an environment by one species for another, in the formation of a substrate on which another species settles, etc.
3. Phoric connections- these are connections in which one species takes part in the distribution of another. An example of this type of connection is the transfer of seeds, spores and pollen by animals. (zoochory), and the transfer of some animals (smaller) by others (phoresy).
4. Factory connections- these are connections in which a given species uses excretory products or dead remains of other species for its structures.
For example, birds use grass leaves, mammal hair, down and feathers of other bird species to build their nests.
For the normal development of a particular species, its living conditions must be optimal. To characterize living conditions, there are two criteria: physiological and synecological optimum.
Physiological optimum- this is a combination of all abiotic factors favorable for the species, at which the fastest rates of growth and reproduction are possible.
Synecological optimum- this is a biotic environment in which a species experiences the least pressure from enemies and competitors, which allows it to reproduce successfully.
Physiological and synecological optimums do not always coincide. An example of this discrepancy could be the mass reproduction of the Hessian fly after particularly harsh winters, which should have had a negative impact on the population of this pest. In normal years, the Hessian fly is severely exterminated by several species of its natural enemies. However, due to poor frost resistance, the enemies of the Hessian fly almost completely die. This allows the Hessian fly to restore its numbers.
Ecological niches. An ecological niche is the position of a species that it occupies in the general system of biocenosis. This is a complex of its biocenotic connections and requirements for abiotic environmental factors.
According to Elton's (1934) definition, an ecological niche is this is a place in a living environment, the relationship of the species to food and enemies.
The ecological niche reflects the participation of a given species in the biocenosis. In this case, what is meant is not its territorial location, but the functional manifestation of the organism in the community.
The existence of a species in a community is determined by the combination and action of many factors. When determining whether a particular species belongs to a particular niche, it is necessary to take into account the feeding habits of these organisms and their ability to obtain food.
Thus, plants, taking part in the formation of the biocenosis, provide the existence of a number of ecological niches. These may be niches that include organisms that feed on root tissue or leaf tissue, flowers, fruits, etc.
Each of these niches includes groups of organisms that differ in species composition. Thus, the ecological niche of root beetles includes both nematodes and the larvae of some beetles (May beetles, click beetles). And the niche that sucks plant juices includes bugs and aphids.
Thus, specialization of species in relation to food resources reduces competition and increases the stability of community structure.
There are different types of resource sharing:
1. This is the specialization of morphology and behavior in accordance with the type of food, for example, the beak of birds can be adapted for catching insects, gouging holes, cracking nuts, and so on.
2. Vertical separation, for example, between the inhabitants of the tree crown and the forest floor.
3. Horizontal separation between inhabitants of different microhabitats. For example, there is a division of birds into ecological groups based on the place of their feeding: air, foliage, trunk, soil.
Specialization of a species in nutrition, use of space, time of activity and other conditions is characterized as a narrowing of its ecological niche. And reverse processes are like its expansion.
The narrowing or expansion of the ecological niche of a species in a community is greatly influenced by competitors. According to the rule formulated by Gause, two species do not coexist in the same ecological niche.
A way out of competition can be achieved by diverging requirements for the environment, changing lifestyles, that is, delimiting ecological niches. Only in this case do they acquire the ability to coexist in the same biocenosis.
For example, in European Russia there are closely related species of tits, the isolation of which from each other is due to differences in habitat, feeding areas and prey sizes. The ecological differences between these tit species are reflected in a number of small details of the external structure, such as the length and thickness of the beak.
Numerous orders of animals that feed on grass include steppe biocenoses. Such as ungulates (horses, sheep, saigas) and rodents (gophers, marmots, mice). All of them form one functional group of the biocenosis – herbivores. However, the role of these animals in consuming plant mass is different. Thus, ungulates (horses, cattle) eat mainly tall, most nutritious grasses, biting them at a considerable height (5-7 cm) from the surface. Marmots living here choose food among the grass, thinned out and crushed by their hooves. Marmots settle and feed only where there is no high grass.
Smaller animals - gophers - prefer to collect food where the grass is more disturbed. Here they collect what is left from feeding ungulates and marmots.
Between these three groups of herbivores that form the zoocenosis, there is a division of functions in the use of herbaceous biomass.
The relationships that have developed between these groups of animals are not competitive in nature, but on the contrary ensure their higher numbers.
The ecological niches of species vary in space and time. Often in a biocenosis, the same species can occupy different ecological niches during different periods of development. Thus, a tadpole feeds on plant foods, while an adult frog is a typical carnivore. Therefore, they are characterized by different ecological niches and specific trophic levels.
In insectivorous birds, winter ecological niches differ from summer ones. And so on.
The ecological niche of a species is significantly influenced by interspecific and intraspecific competition.
With interspecific competition, the habitat zone of a species can be reduced to optimal boundaries, where it has an advantage over its competitors.
If interspecific competition narrows the ecological niche of a species, 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 biocenetic connections.
Ecological structure of biocenosis. Biocenoses consist of certain ecological groups of organisms that express the ecological structure of the community. Ecological groups of organisms, occupying similar ecological niches, may have different species composition in different biocenoses. Thus, in humid areas, hygrophytes (plants of excessively moist habitats) dominate, and in arid conditions, xerophytes (plants of dry habitats) dominate.
The ecological structure of the biocenosis is significantly influenced by the ratio of groups of organisms that share a similar type of nutrition. For example, in forests saprophages (animals that feed on the corpses of other animals, destroying rotting remains) predominate; in steppe and semi-desert zones, phytophages (animals that feed only on plant foods) predominate.
In the depths of the ocean, the main type of feeding of animals is predation, and in the surface, illuminated zone there are many species with a mixed type of feeding.
Differences in the ecological structure of the biocenosis are most clearly manifested when comparing communities of organisms in similar biotopes of different regions. For example, marten is in the European taiga and sable is in the Asian taiga. These species occupy similar ecological niches and perform the same functions. These species determine the ecological structure of the community and are called replacing or vicarious.
Thus, the ecological structure of a biocenosis is its composition of ecological groups of organisms that perform certain functions in the community in each ecological niche.
The ecological structure of the biocenosis, in combination with the species and spatial structure, with the characteristics of the ecological niche, serves as a macroscopic characteristic of the biocenosis.
And macroscopic characteristics make it possible to determine the properties of a particular biocenosis, determine its stability in space and time, and also anticipate the consequences of changes caused by the influence of anthropogenic factors.
Border effect. The most important feature of the structural characteristics of biocenoses is the presence of community boundaries. However, it should be noted that these boundaries are rarely clear-cut.
As a rule, neighboring biocenoses gradually transform into one another, forming transitional or border zones on the border of two biocenoses, characterized by special conditions.
Here, the typical conditions of neighboring biocenoses seem to intertwine. Plants characteristic of both biocenoses grow in the transition zone. The abundance of plants in the border zone attracts a variety of animals, so the border zone is often richer in life than each of the biocenoses separately. That is, with the spatial transition of one biocenosis to another, the number of ecological niches increases.
In these transition zones, a concentration of species and individuals occurs, and the so-called edge effect is observed.
Example of edge effect...................Pure steam - sowing
Biogeocenosis. Living organisms and their inanimate environment are inseparably connected with each other and are in constant interaction. These components form a more complex ecological community, an ecosystem or biogeocenosis.
The term biogeocenosis was proposed in 1940 by the Russian ecologist Sukachev. By his definition biogeocenosis(from Greek – bios-life, geo-earth, cenosis-general) is a stable self-regulating ecological system in which organic components are inextricably linked with inorganic ones.
The basic functional unit in modern ecology is the ecosystem. The term ecosystem was first proposed by the English ecologist Tansley in 1935.
By his definition ecosystem is any collection of organisms and inorganic components in which the circulation of substances can take place.
In other words, the combination of a specific physicochemical environment (biotope) with a society of living organisms (biocenosis) forms an ecosystem.
There is an opinion that the concept biogeocenosis more reflective structural characteristics macrosystem being studied, whereas in the concept ecosystem First of all, its functional essence is invested.
In fact, there is no fundamental difference between these terms. And in the modern view, biogeocenosis and ecosystem are synonymous.
The vertical structure of a broad-leaved forest can be represented by the following diagram:
1. Tree layer
2. Shrub layer
3. Herbaceous layer
4. Ground layer
5. Litter
6. Topsoil
7. Subsoil
8. Mother breed
The structure of the biocenosis and the pattern of interaction between its components.
Ecotop
Atmosphere Soil-ground
(climatope) (edaphotope)
Biotope
Vegetation Animals
(phytocenosis) (zoocenosis)
Microorganisms
BIOTIC COMMUNITIES
When it comes to ecosystems, biotic community commonly understood biocenosis, because the community is the population biotope- places of life of the biocenosis.
Biocenosis- ϶ᴛᴏ an organismal system consisting of three components: vegetation, animals and microorganisms. In such a system, individual species, populations and groups of species can be replaced by others, respectively, without much damage to the community, and the system itself exists by balancing the forces of antagonism between species. The stability of a community is determined by the quantitative regulation of the numbers of some species by others, and its size depends on external reasons - on the size of the territory with homogeneous abiotic properties, i.e. e. biotope. Functioning in continuous unity, the biocenosis and biotope form biogeocenosis, or ecosystem. The boundaries of the biocenosis coincide with the boundaries of the biotope and, therefore, with the boundaries ecosystems. Biotic community (biocenosis) - more high level organization than the population that is it integral part. The biocenosis has a complex internal structure. The species and spatial structures of biocenoses are distinguished.
It is important to note that for the existence of a community, not only the size of the number of organisms is important, but even more important is species diversity, which is the basis of biological diversity in living nature. According to the Convention on Biological Diversity of the United Nations Conference on Environment and Development (Rio de Janeiro, 1992), under biodiversity It is common to understand diversity within a species, between species and the diversity of ecosystems.
Diversity within a species is the basis for stability in the development of populations; diversity between species and, consequently, populations is the basis for the existence of a biocenosis as the main part of an ecosystem.
Species structure The biocenosis is characterized by species diversity and the quantitative ratio of species, depending on a number of factors. The main limiting factors are temperature, humidity and lack of food resources. For this reason, biocenoses (communities) of ecosystems at high latitudes, deserts and high mountains are the poorest in species. Organisms whose life forms are adapted to such conditions can survive here. Biocenoses rich in species are tropical forests, with a diverse fauna, and where it is difficult to find even two trees of the same species standing next to each other.
Typically, natural biocenoses are considered species-poor if they contain tens and hundreds of species of plants and animals, while rich - several thousand or tens of thousands of species. Richness of species The composition of biocenoses is determined by either the relative or absolute number of species and depends on the age of the community: young, just beginning to develop, are poor in species compared to mature or climax communities.
Species diversity– this is the number of species in a given community or region, i.e. it has a more specific content and is one of the most important both qualitative and quantitative characteristics of the sustainability of an ecosystem. It is interconnected with the diversity of environmental conditions. The more organisms find conditions in a given biotope that meet environmental requirements, the more species will settle in it.
Species diversity in a given habitat is called α- variety, and the sum of all species living in all habitats within a given region, β -diversity. Indicators for quantitative assessment of species diversity, diversity indices, are usually the ratio between the number of species, the values of their abundance, biomass, productivity, etc., or the ratio of the number of species per unit area.
An important indicator is the quantitative relationship between the number of species. It’s one thing when among a hundred individuals there are five species in the ratio 96:1:1:1:1, and another thing if they have a ratio of 20:20:20:20:20. The latter ratio is clearly preferable, since the first grouping is much more uniform.
The most favorable conditions for the existence of many species are characteristic of transition zones between communities, which are called tokens, and the tendency to increase species diversity here is called edge effect.
The ecotone is rich in species primarily because they come here from all border communities, but, in addition, it can contain its own characteristic species, which do not exist in such communities. A striking example of this is the forest “edge”, on which the vegetation is lush and richer, significantly more birds nest, more insects, etc., than in the depths of the forest.
Species that predominate in numbers are called dominant, or simply – the dominants of a given community. But even among them there are those without which other species cannot exist. They are called edifiers(Latin – “builders”). They determine the microenvironment (microclimate) of the entire community and their removal threatens the complete destruction of the biocenosis. As a rule, edificators are plants - spruce, pine, cedar, feather grass, and only occasionally - animals (marmots).
"Minor" species - small in number and even rare - are also very important in the community. Their predominance is a guarantee sustainable development communities. In the richest biocenoses, almost all species are small in number, but the poorer the species composition, the more dominant species there are. Under certain conditions, there are “outbreaks” in the number of individual dominants.
To assess diversity, other indicators are used that significantly complement the above. Species abundance– the number of individuals of a given species per unit area or volume of space they occupy. Degree of dominance – the ratio (usually in percentage) of the number of individuals of a given species to the total number of all individuals of the group under consideration.
At the same time, the assessment of the biodiversity of the biocenosis as a whole by the number of species will be incorrect if we do not take into account size of organisms. After all, the biocenosis includes both bacteria and macroorganisms. For this reason, it is extremely important to group organisms into groups that are similar in size. Here you can approach from the point of view of taxonomy (birds, insects, Asteraceae, etc.), eco-morphological (trees, grasses, mosses, etc.), or generally in terms of size (microfauna, mesofauna and macrofauna of soils or silts, etc. . P.). At the same time, it should be borne in mind that within the biocenosis there are also special structural associations - consortia. Consortium– a group of heterogeneous organisms that settle on the body or in the body of an individual of a particular species – central member consortium - capable of creating a certain microenvironment around itself. Other members of the consortium can create smaller consortia, etc., i.e., consortia of the first, second, third, etc. order can be distinguished. From here it is clear that a biocenosis is a system of interconnected consortia.
Most often, the central members of the consortium are plants. Consortia arise based on close, diverse relationships between species (Fig. 4.1).
Species structure of the biocenosis. The species structure of a biocenosis is understood as the species composition and the ratio of the number of species or their mass. Species composition and species richness depend on environmental conditions. There are biocenoses poor (oligomixed) and rich (polymixed) in species. For example, the first deposits of blue-green algae on cooling lava or a colony of sulfur bacteria in sulfur springs are more beautiful than rare, poor biocenoses. Complex multi-species communities are usually found in nature. Thus, in the forest-tundra of Western Siberia in the vicinity of the city of Salekhard, 65 species of lichens, 87 mosses, 166 vascular plants, 144 fungi, about 600 insects, 62 birds were identified in the community of organisms. 14 species of mammals (Novikov, 1979). The highest species richness (biodiversity) is found in tropical forest communities and coral reefs.
The number of plant species recorded in a certain area (1 m3. 100 m3) indicates the species richness of the phytocenosis. A complete list of species, compiled on the basis of a description of a number of survey sites within each community, is the species richness of the phytocenosis. For example, in a pine forest with undergrowth in the Moscow region on an area of 0.5 hectares, 8 species of trees, 13 species of shrubs, 106 species of shrubs and grasses, and 18 species of mosses were found. In the Central Russian meadow steppes, characterized by floristic richness, there are up to 120 or more species per 100 m2 alone higher plants.
An example of very large floristic richness is tropical rainforests. Thus, in the forests of Sri Lanka there are about 1,500 tree species alone, in the Amazon basin there are even more - 2,500. On the territory of Russia, some phytocenoses in the Sikhote-Atin mountains in Primorye, complex oak forests and upland meadows in the forest zone are characterized by high diversity. At the same time, in dark spruce and beech forests, no more than 10 species of flowering plants can be found per 100 m2.
The main reason for the poverty of the herbaceous community in spruce forests is heavy shading. Illumination as an environmental factor here is much lower than the optimum required for the life of flowering plants. With extreme heat deficiency, as in the northern tundras or arctic deserts, moisture deficiency, as in waterless hot deserts, oxygen deficiency, as in reservoirs heavily polluted by sewage, i.e., wherever one or more environmental factors deviate far from the optimal living standards, communities are greatly impoverished, since few species can adapt to extreme conditions.
The species composition of biocenoses also depends on the duration of their existence. Young, emerging communities have a smaller set of species than established mature ones. “Cultural” biocenoses - fields, gardens, vegetable gardens, plantations of seaweed grown in suspended culture, marine invertebrate farms, fish ponds, etc. - are also poorer in species than natural systems - meadows, steppes, forests, reservoirs. Species uniformity and people specifically support the poverty of agrocenoses using complex system agrotechnical measures and constantly fighting weeds and plant pests.
Species of the same size class that are part of a biocenosis vary greatly in abundance. Some of them are rare, others are so common that they determine the appearance of the biocenosis. In each community, one can distinguish a group of the main, most numerous species, the connections between which are actually decisive in the functioning of the biocenosis.
Species that predominate in numbers dominate the community and are its dominants. They form the core of the species. For example, in the spruce forests of Russia, spruce dominates among the trees. in the grass cover - wood sorrel, in the bird population - wren, robin, chiffchaff, among mouse-like rodents - red and red-gray voles.
In all biocenoses, the smallest forms - bacteria and other microorganisms - predominate numerically. Therefore, any estimates refer to one-dimensional species.
In addition to a relatively small number of dominant species, the community includes many small and even rare forms. They are also important for the life of the biocenosis, since they create its species richness, increase the diversity of biocenotic connections and serve as a reserve for replenishment and replacement by the dominant. Therefore, they give the biocenosis stability and ensure the reliability of its functioning in different conditions.
To assess the role of an individual species in the species structure of the biocenosis, various indicators based on quantitative accounting are used. The abundance of a species is the number of individuals of a given species per unit area or volume. Sometimes, instead of the number of individuals, the value of their total mass is used. The frequency of occurrence characterizes the distribution of 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 degree of dominance reflects the ratio of the number of individuals of a given species to the total number of all individuals of the group under consideration.
Although dominant species dominate the community, they do not all equally influence the biocenosis. Plants that mainly determine the specific habitat of a plant community are called edificators (from the Latin aedificator - builder). Hence. edificators are types of organisms that predetermine the conditions for the existence of other types of organisms, or. otherwise, the species that contribute the most to habitat. The concept of “edifier” was first used by G.I. Poplavskaya in 1924. According to Poplavskaya. edificators are the creators of the phytogenic environment of a community. A species becomes an edifier in a specific environment in a specific cenosis.
For example, a birch tree that settles in a cleared coniferous forest, that is, on podzolized soil, soon greatly changes it. Absorbing minerals from the soil, it returns many of them in the form of litter - leaves, root hairs, root tips, pieces of bark, branches. Nitrogen and ash elements such as calcium are especially strongly extracted from the soil and returned back, that is, they are most intensively involved in the cycle. In soil enriched with nitrogen, the processes of nitrification—the oxidation of ammonified dead organic matter that enters the litter—intensify. It involves the conversion of ammonium to nitrous acid, carried out by some genera of bacteria, and then the further oxidation of nitrous acid into nitric acid, carried out by other genera of bacteria.
Due to the increase in ash content and especially the enrichment of calcium. soil acidity decreases. Enrichment with humus leads to an improvement in structure and a change in color - the soil becomes darker. As a result, it thaws earlier and warms up better. And this, in turn, leads to an increase in the biological activity of the soil. Revitalizing the activity of soil matter and flora increases the porosity and adsorption capacity of the upper layers. Gradually, the soil from podzolic, as it was after cutting down the coniferous forest, becomes sod-podzolic, and with the long-term existence of birch forests - even soddy. The soil population is changing.
However, the edificatory activity of birch is manifested not only in soil formation, but also in changes in terrestrial environmental conditions: shading created by its crowns, the influence on light, water and temperature regimes, the presence of organisms accompanying it - all this enhances the impact of birch on environment.
The environment-forming actions of different plants are different. Very strong edificators are alder, aspen, oak, spruce; from herbs - legumes, cereals, coltsfoot, tansy, wormwood, knotweed, wood lice (Ponomareva, 1978).
For the northern and central parts of the forest zone of Eurasia, the main edificators are spruce and fir. Of all tree species, they change the habitat conditions to the greatest extent: they strongly shade the subcanopy space, increase the acidity of the soil, and lead to their podzolization. Only those tree species that grow quickly and are able to be the first to take over free space coexist with such edificators, which can be observed in spruce-deciduous and fir-deciduous mixed forests, usually with birch and aspen. In the herbage of spruce forests, the common sorrel feels especially good, its strong fruiting and ripening of seeds indicate successful growth. Strawberries, on the contrary, are in a depressed state, no more than 1-3 flowers develop on its thin generative shoots, and only in some places small and dry fruits can be found.
An edifier can be a single individual, for example a spruce. capable of significantly changing the environment and influencing surrounding plants, as well as a group of individuals, i.e., a collective of plants. The edificatory role of pine is predominantly manifested in the collective.
The main edifiers of terrestrial biocenoses are certain plant species. However, in some cases animals can also be edificators. Thus, in territories occupied by marmot colonies, the digging activity of these animals mainly determines the nature of the landscape, as well as the microclimate and growing conditions of plants.
If edificatory species create a habitat, then indicator plants indicate the nature of the growing conditions. Thus, the presence of wood sorrel in the forest zone indicates close to optimal moisture conditions and a significant richness of soils in nutritious minerals. The appearance of blueberries indicates somewhat excess moisture and some deficiency of mineral nutrients. Lingonberries indicate a lack of moisture and soil fertility; mosses (cuckoo flax and sphagnum) - for excessively excessive moisture, deficiency of minerals, lack of oxygen for root respiration and the presence of peat formation processes.
Expressive examples of indicator plants are given by I. N. Ponomareva (1978). Thus, the presence of hazel, bird cherry and elderberry in the undergrowth of northern forests indicates soil fertility. The presence of lily of the valley here further confirms this. Large feather grass from small ones! the participation of fescue and forbs in the steppe or dry steppe zone indicates the presence of rich chernozems. At the same time, the appearance of even a small amount of Potentilla erecta indicates a decrease in soil fertility, and the presence of white beetle sticking out in meadows is a sign of their degradation.
The presence of some species indicates not only the growing conditions, but also the changes in plant communities that have occurred. For example, oak anemone, found in spruce or mixed forests, indicates the previous existence of an oak-type phytocenosis in this territory.
Biocenoses are named by edificator plants and indicator plants. For example, sorrel spruce forests, blueberry spruce forests or green moss forests. For the steppes, fescue-feather grass, grass-forb and similar biocenoses are distinguished.
Animals also participate in the formation of the plant community. The ways in which they influence the species composition and species ratio may be different. This includes spreading plant buds, loosening or compacting the soil, eating plants, and selective or complete trampling. The influence of animals on plant communities can be so great that the formation and existence of certain types of phytocenoses is possible only with the constant influence of animals. For example, typical steppe communities dominated by tussock grasses, primarily feather grass, are preserved only with moderate grazing by herbivorous artiodactyls. The famous North American prairies are believed to have been supported by bison, antelope, elk, Virginia deer and other animals. First of all, animals eat legumes and forbs, which, moreover, are more sensitive to trampling. Affects the species composition and amount of excrement. Perhaps the lack of grazing explains the fact that even within three decades the vegetation of typical prairies on fallow lands is not restored (Ipatov and Kirikova, 1997).
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