The social vole Microtus socialis (Сricetidae, Rodentia) in the westernmost part of its geographic range

According to the literature, there are several isolated range segments of Microtus socialis across the Palearctic, within which the distribution of the species has mosaic pattern. The westernmost range segment is located in the south of Ukraine covering steppe areas of the Crimea and southern Ukraine and stretching from the lower reaches of the Dnipro to Melitopol in the east and to Dnipro in the north. The social vole is represented in this centre of distribution by the subspecies Microtus socialis nikolajevi. The Yahorlyk Kut Peninsula in Kherson Oblast represents the westernmost edge of the subspecies’ range, where local conditions have practically remained in their natural state and the social vole (Microtus socialis) has a substantial population density. The Yahorlyk Kut Peninsula separates Yahorlyk Bay of the Black Sea from Tendra Bay. The western part of the peninsula (5540 ha) constitutes the ‘Yahorlyk Kut’ protected area of the Black Sea Biosphere Reserve, where steppe habitats have been partially preserved in their natural state in contrast to the area of the former bombing range, which was attached to the reserve in 1998, where the steppe has slightly transformed. This is the only area of typical halophytic wormwood–grass steppe that has avoided continuous ploughing and irrigation. The population density of M. socialis depends on the microrelief, hydrological conditions, and natural spring flooding. The disturbance of vegetation and soil cover due to fires and grazing disrupt the natural population dynamics of social voles. Recovery takes 2 to 3 years. After the cessation of the impact of hydrological, pyrogenic, or pascual factors, population density of the social vole in different habitats becomes balanced. Over 30 years, the population density of Microtus socialis ranged from 200 to 7000 ind./ha (on average 1800 ind./ha). The amplitude of fluctuations in the value of relative abundance in the periods between peaks is about 15 units. The cyclicity in population dynamics of the social vole in the Yahorlyk Kut Peninsula is 6–8 years. The dynamics of the number of social voles is determined by abiotic and biotic factors, which are also cyclical. Disturbances in the cyclicity of population dynamics can occur due to ‘force majeure’ situations of both natural and anthropogenic nature.