ИСТИНА

What part of a population contributes to the gene pool of the next generations? This information could serve as an important indicator of the viability of populations, because it determines its genetic polymorphism and future existence. Based on that, the concept of effective population size Ne was introduced in population genetics (WRIGHT 1931, 1938). In practice, population size is measured by the number of breeding males and females as recommended by IUCN, because Guidelines for Using the IUCN Red List (2010) state that "mature individuals that will never produce new recruits should not be counted". However, mature individuals whose descendants are infertile do not contribute to the future gene pool either, nor are non-breeding animals. Long-term individual-based studies of Arctic foxes on Mednyi Island (The Commander Islands, Northern Pacific) show that the lack of information about second-generation litters of the breeding individuals can lead to significant measurement errors in the empirical measurement of the effective population size. According to our findings, about half of all animals who lived up to at least one year will take part in the reproduction (54.5 ± 25.6 %, M ± SD; 95 % CI = 40.3 - 68.2 %). But only 19.8 ± 14.2 % (95 % CI = 11.9 - 27.7 %) will have second-generation litters (N = 15 - the number of years included in the analysis). This means that most of the breeding individuals of the Mednyi Arctic fox population do not contribute to the future gene pool because their offspring die before breeding. It is too early to say whether this situation is typical for mammalian populations but this study suggests that: (1) estimation of effective population size based on empirical measurements of breeding individuals produces a largely overestimated number of individuals affecting the gene pool; and (2) small, isolated natural populations, like the Arctic foxes on Mednyi Island, whose recorded adult population is about 100, can have a "reproductive core" of only two dozen animals. The surveys were financed by grants of the Russian Foundation of Basic Sciences