Biocenosis(redirected from biocenoses)
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the totality of plants, animals, and microorganisms that inhabit a sector of land or a body of water and are characterized by definite relationships both among themselves and with abiotic factors of the environment. The term “biocenosis” was proposed by the German biologist K. Mobius in 1877. A biocenosis is the complex of organisms of a biogeocenosis which forms as a result of the struggle for existence, natural selection, and other evolutionary factors. Three groups of organisms are distinguished in a biocenosis according to their participation in the biogenic cycle of substances. The first group is the producers—autotrophic organisms—which produce organic substances from inorganic substances; the chief producers in all biocenoses are green plants. The activity of the producers determines the initial stock of organic substances in the biocenosis. The second group is the consumers— heterotrophic organisms—which feed at the expense of the autotrophic organisms. Consumers of the first order are herbivorous animals, as well as parasitic bacteria, fungi, and other achlorophyllous plants that develop at the expense of live plants. Consumers of the second order are predators and parasites of herbivorous organisms. Consumers of the third and fourth orders (hyperparasites, superparasites, and such) exist, but altogether there are no more than five links in food chains. At each successive trophic level the quantity of the biomass decreases sharply. The activity of the consumers makes possible the transformation and transportation of organic substances within the biocenosis, their partial mineralization, and the dispersion of energy accumulated by the producers. The third group is the reducers—animals that feed on the decomposed remains of organisms (saprophages), especially nonparasitic heterotrophic organisms. Reducers make possible the mineralization of organic substances and their conversion to an assimilated state by the producers.
The interrelationships of organisms within a biocenosis are diverse. In addition to trophic links, which determine food chains and which are sometimes very unusual (parasitism, symbiosis), there are links based on the fact that some organisms become substrates for others (topical relations), create the necessary microclimate, and so on. It is often possible to trace groups of species in a biocenosis that are connected with a definite species and are completely dependent on it (“consortions”).
The division into smaller subordinate units—merocenoses (that is, naturally composed complexes that are dependent in their entirety on the biocenosis—for example, the complex of inhabitants of rotting oak stumps in an oak forest)—is characteristic for biocenoses. If animals (for example, bats in a cave biocenosis) rather than autotrophs serve as the energy source for a biocenosis, such a biocenosis is dependent on a supply of energy from without and is incomplete—in essence a merocenosis. Other subordinate groupings (for example, synusia) may be distinguished in biocenoses. Vertical grouping of organisms (biocenotic strata) is also characteristic of biocenoses. The number, developmental stages, and activity of certain species change in an annual cycle, and regular seasonal aspects of biocenoses are created.
A biocenosis is a dialectically developing whole that changes as a result of the activity of its components; as a consequence of this, regular changes and replacements occur in the biocenosis (succession), which may lead to the reconstitution of severely disrupted biocenoses (for example, forests after a fire). A distinction is made between saturated and unsaturated biocenoses. In a saturated biocenosis, all ecological niches are occupied, and the establishment of a new species is impossible without the destruction or subsequent displacement of some component of the biocenosis. Unsaturated biocenoses are characterized by the possibility of the settlement within them of new species without the destruction of other components. It is possible to distinguish primary biocenoses, which are formed without the influence of man (virgin steppe or forest), and secondary biocenoses, which are changed by the activities of man (forests grown to replace those removed, the populations of water reservoirs). Agrobiocenoses are a special category in which the complexes of basic components are consciously regulated by man. Between the primary biocenosis and the agrobiocenosis there is a complete range of intermediate types. The study of biocenoses is important for the rational management of land and water areas, since only a proper understanding of the regulative processes of biocenoses enables man to withdraw a portion of the production of a biocenosis without disrupting or destroying it.
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