On ecology of sibling species Microtus arvalis Pallas, 1779 and Microtus rossiaemeridionalis Ognev, 1924 (Rodentia, Cricetidae) in tsimlyansk sands

Ecological features and circadian activity of the common vole sibling speci es were studied upon joint and separate occurrences. Both species had a sim ilar abundance but different biotopical distribution. Microtus arvalis-chro mosome form "obscurus" populated the studied territory more uniformly the s tudied territory. M. rossiaemeridionalis tended to occur in humid coenoses. In case of joint occurrences, the sibling species occupied different regio ns of biotopes and the rhythms of their activity change, as a rule, in anti phase. Separation of the spatial and temporal niches of these species is co nsidered as possible avoidance of competition between the closely related s pecies.