Biocoenosis

BIOCOENOSIS (from Greek bios-life and koinos-common), a biological concept introduced in 1877 by Möbius to designate the dynamically balanced population system established under given ecological conditions; in other words, a biocoenosis is a community of living organisms that inhabits a certain homogeneous tract of nature and has a definite species composition. The members of a biocoenosis depend on each other and consequently are in a state of mobile equilibrium maintained through self-regulation. Along with species common in other places as well, every biocoenosis possesses certain guiding forms peculiar only to it. The concept of biocoenosis is quite elastic. For example, the animal and plant world of an oak forest forms a biocoenosis. However, an anthill in this forest and a hazel bush (with its population) at the forest edge are also biocoenoses of a smaller scale. The dependence between members of a biocoenosis is most easily seen in the relations between the plants constituting it, on the one hand, and the animals, on the other. Plants are the primary producers of complex organic compounds, of which animals are direct or indirect consumers. In turn, animals produce CO₂ and nitrogenous salts, which plants need. A similar dependence exists between animal members of a biocoenosis: for example, predators depend entirely for their existence on the species composition and quantity of the herbivorous inhabitants of the biocoenosis. The tract of nature occupied by a certain biocoenosis (taking the term in a broader sense) is called a biotope, i.e., a biocoenosis is the population of a biotope. Plant biocoenoses received the name of plant communities in botany. The concept of biocoenosis is best developed in hydrobiology and somewhat weaker in terrestrial ecology (see). In parasitology, this concept is still applied very little. However, even here its systematic application is extremely useful in analyzing complex epidemiological relations. For example, the epidemiology of malaria is determined by the equilibrium established within the biocoenosis: plasmodium-human-mosquito-livestock (see Malaria). In a broad sense, every animal species, with the entire aggregate of parasites inhabiting it, represents a biocoenosis. However, the parasitic biocoenosis of the same host varies somewhat in different parts of the distribution area of the host animal (for example, the parasitic fauna of dogs in Europe and Turkestan). Therefore, the biocoenosis of a given host species can be subdivided into several geographical biocoenoses of a lower order (for example, the biocoenosis of European dogs, the biocoenosis of dogs in Turkestan). The parasitic biocoenosis of many hosts can be successfully divided into biocoenoses of a lower order according to another principle as well, namely, depending on the habitat of the parasites in the host's body. Thus, biocoenoses of the intestine, blood, and external integuments are quite naturally outlined. Each of them is characterized by completely definite conditions of existence (temperature, conditions of nutrition, respiration, etc.) and possesses its own quite definite fauna.