The Impact of Spacing Behavior in Microtine Rodents on the Dynamics of Least Weasels Mustela nivalis: A Hypothesis

Abstract

The dependence of the least weasel Mustela nivalis on certain microtine species, especially Microtus, has been suggested by several studies. Evidence has been collected from analyses of food selection (fecal droppings) and correlations between weasel numbers and Microtus densities. I propose the hypothesis that the differences in the social behavior between the two main groups of vole prey, namely Microtus and Clethrionomys, could be a probable reason for the least weasel's dependence on some Microtus species. I also suggest that in Europe Mustela nivalis depends on Microtus agrestis in particular (and also on M. arvalis) primarily because in these Microtus species, as well as in M. oeconomus, the home ranges of breeding females are small and can overlap, and the young females can breed within the home ranges of their mothers. Consequently, densities of these species in spring and early summer will easily exceed the threshold density needed to support a breeding Mustela nivalis female in its restricted home range (1-2 ha). In Clethrionomys, territories of breeding females are larger than the home ranges in Microtus, and they do not overlap. In addition, young maturing Clethrionomys females have to disperse from the territories of their mothers. Therefore densities of Clethrionomys in spring and early summer do not usually exceed the threshold necessary for the successful breeding of Mustela nivalis, not even in the spring of cyclic peak years. I discuss the atypical dynamics of microtines and least weasels in Finnish Lapland in the early 1980s in light of this hypothesis.