From Big Medical Encyclopedia

FERTILITY — quantitative characteristic of process of reproduction of live organisms. It is expressed by the work of number of descendants in one generation (number of berries, number of young people in a dung, number of eggs in a laying, etc.) on number of generation in a year or for average life expectancy of parental generation.

Potential P. is never implemented owing to considerable death of descendants under the influence of various biotic and abiotic factors of the environment. The influence of natural selection is stronger, the P. Vysokaya P. connected with action is higher natural selection (see), first of all it is characteristic of parasites, in particular of endoparasites to which a difficult life cycle of development and extraordinary development of system of a reproductive organs at the expense of a reduction of other systems of an organism are inherent (c. N of page, etc.). Various devices for protection of posterity lead to sharp reduction of influence of natural selection that is followed by decrease in the Item. This decrease in P. connected with reduction of mortality and increase in survival is observed in the most different systematic groups. So, on one cub every time a tsetse fly, nek-ry bird species (silly fellow) bring, mammals and, as a rule, the person. In general it is possible to claim that for animals from high P. the unstable type of dynamics of number with a bigger amplitude of fluctuations of number, and is more characteristic of views from low P. — steadier type of dynamics of number. However there are many exceptions. So, for the organisms living in the constant environment, napr for many endoparasites, the steady type of dynamics of number is characteristic.

To the item it is subject to geographical variability. In an optimum area (see) where pressure of natural selection is weakened, P. can be lower, than on the periphery of an area. In a pessimum of an area mortality is not compensated to P. and the number of a look can be supported only due to migrations from districts with higher number and smaller mortality of individuals. As P.'s characteristic is quite often used a concept the potential of reproduction (r) estimated on a formula: Ó = (s*n) g , where s — a ratio of number of floors, n — number of juveniles in each generation, g — number of generation in a year. E.g., the cheese fly (Piopila haesi) has s = 0,5, the number of eggs in a laying (n) makes 480, g — 30. Therefore, the potential of reproduction of this look (r) is expressed of 240 30 . The posterity of one female of a hop plant louse (Phorodon humeli) for one summer would reach 10 22 (if to arrange the number of descendants to one line, then the strip of 2500 light years would turn out).

The concept «fertility» and methodical bases of calculation of P. are used as one of vital rates (see. Birth rate ).

See also Reproduction .

Bibliography: Kashkarov D. N. Fundamentals of zooecology, M. — L., 1938; JI e to. Animal numbers and its regulation in the nature, the lane with English, M., 1957; Timofey in-P e with about in with to and y N. V., Baneberries of H. N and I would be l about to about in A. V. Short sketch of the theory of evolution, M., 1977; The Factors influencing fertility under the editorship of K. R. Austen and J. S. Perry, lane with English, M., 1970; F and and l to about in with to Pi y Century. A biological rhythm of fertility and regulation of birth rate, the lane with polsk., Warsaw, 1976.

H. N. Vorontsov.