Winter in Hokkaido

摘要

In Hokkaido, winter seems to be the most interesting season, both for voles and for those studying voles. The former spend the winter producing strong direct density-dependence in their population dynamics (Stenseth et al. 1998), the latter spend much effort on tracing the impact of social interactions among voles on their survival and on density (Ishibashi et al. 1998a). The importance of winter survival for density regulation processes has been postulated by two sets of hypotheses on population regulation: first by the hypotheses which explain vole dynamics by predator-prey interactions, with special reference to winter duration and snow cover (Hansson and Henttonen 1985, 1988); then - more indirect - by the hypotheses linking demographic processes with kinship among vole females and stressing the importance of winter survival for the maintenance of female relatedness (Kawata 1990; Lambin and Krebs 1991, 1993). In Hokkaido little is known about interactions between gray-sided voles and their predators; but the effects of kinship on winter survival of voles are fairly well known thanks to the recent study of Ishibashi et al. (1998a).