On the ecology of the forest lemming (Myopus schisticolor Lill.) on the southern periphery of the area

The article describes the state and dynamics of the forest lemming population located in Karelia at the southern borders of the population distribution: abundance, biotopic distribution, seasonal migrations, nutrition, reproduction, ecological structure of the population, and long-term population changes. This is the result of long-term expeditionary and stationary studies (1957-2018). The determined abundance indicators (0.26 specimens per 10 trap trenches per day; 1.9 % in the total catches of small mammals) were relatively low due to the location at the southern periphery of the range. It was also established that lemmings were strictly confined to coniferous green moss forests with a powerful moss and shrub cover; at that, the lacy character of the animals distribution was preserved within the biotope, as well as seasonal migrations. The migrations are often massive, especially in the years of intensive reproduction. Young wintered animals form the basis of the migrants. The high specialization in nutrition by green mosses typical for this species was noted. The breeding period lasts from the second half of May to September. The adult wintered animals mainly take part in it, but since the end of July a relatively small proportion of previously arrived broods can reach maturity and participate in breeding. Adult females produce at least 2-3 broods per season, while arrived ones - 1-2 broods of 4.4 + 0.26 pups with fluctuations from 3 to 6. The analysis of the age composition of the harvested animals showed that until June adult wintered animals prevaiedl in the population of forest lemmings. Further, their proportion significantly drops, and in October exclusively arrived lemmings are caught. The sex ratio in the species shifts in the favor of females, judging by the catching of young animals. This indicates the presence of a unique system of genetic sex determination in this species, when along with ordinary females that have two female (XX) chromosomes in the karyotype, there is a significant number of phenotypically normal and fertile females with the male XY karyotype. Long-term changes in abundance are characterized by arrhythmies and a wide amplitude with sharp 15-20-fold rises and deep, very long depressions.