Impact of kinship and familiarity on the annual social organization and population dynamics of Clethrionomys and Microtus voles

In the following we review the results of comparative and experimental studies on the impact of kinship and familiarity on the social systems and population dynamics of microtine rodents. We refer especially to the bank vole Clethrionomys glareolus and the field vole Microtus agrestis. In the beginning of the breeding season the neighbouring territorial Clethrionomys females can be close kin or at least mutually familiar after having spent the winter in an aggregation and probably having nested together. This relatively high degree of kinship or familiarity promotes population growth in the first half of the breeding season, if external factors, such as food and predation, allow it. Kinship should have less or no impact on the social relationships in Clethrionomys males. The impact of relatedness between the breeding females seems to be unimportant in Microtus agrestis. The differences in kin interactions between these species are most probably food-mediated. Field voles use most effectively the rich food resources during the early summer. The preferred dicotyledons are, however, soon depleted and the growth of the graminids slows down as they form seeds during midsummer. As a consequence the breeding females have a strong tendency to disperse and kin groups are very short-lived. This affects the population density negatively during mid-summer. In the bank vole females the lower level of agonism among neighbouring breeding females promotes population growth but exclusive female territoriality throughout the breeding season prevents as a rapid population growth as in the field vole. The role of kin interactions in population dynamics of Clethrionomys and Microtus voles seems to be different, but as a whole it should have an annual character only, and have no or little to do with multiannual population fluctuations of microtine rodents.