The factors causing the suppression of red-backed vole population on the southwestern periphery of the area are analyzed. Trends towards a further reduction in species abundance and distribution area, accompanied by its movement eastwards, are detected. The features of spatial and ecological structure of population typical for the peripheral area include low and unstable abundance, dispersion and mosaic interpopulation groupings, a decrease in reproductive potential, fading fibrillation type of population dynamics etc. A number of mutually exclusive hypotheses, explaining observed processes both from ecological and historical point of view, as a result of interspecific competition and a general shift in the species population strategy, are studied.