Niche dynamics and biodiversity: many rodent species on one marshy meadow

The ecological niche of a species is determined by its tolerance to environmental factors and by interactions with other species, particularly those using the same resource. We assessed spatial niches of four rodent species coexisting in one meadow habitat within the Bialowieza Primeval Forest. Niche characteristics were based on the valorisation of the habitat around live-trapping sites visited by rodents during seven years of the study. The population size of each species was monitored and expressed as an average annual density. The root vole Microtus oeconomus was the most numerous and dominant species, with its density widely fluctuating due to the temporal increases of predation pressure exerted by the weasel Mustela nivalis. During the study period, the spatial niche of the root vole was nearly constant, with only significantly increased tolerance towards shrub covered sites at times of its high population density. However, even a slight niche expansion of the highly abundant root voles displaced accompanying species: the bank vole Myodes (Clethrionomys) glareolus, the yellow necked mouse Apodemus flavicollis and the striped field mouse A. agrarius, from their preferred sites and efficiently decreased rodent species diversity in the studied habitat. This study illustrates a possible mechanism of the direct effect of predation on the dominant prey species population and indirect one on the species diversity changes over ecological time.