Effects of Density and Resources on the Social System of Water Voles

Summary

Water voles (Arvicola terrestris) were studied in two different habitats, marsh and grassland, in Sweden. Voles breeding in the marsh moved to burrows in grassland when becoming nonreproductive, whereas voles breeding in grassland remained there all year. Home ranges in the marsh were much larger than in grassland. Males in the marsh had larger home ranges than females, often including several reproductive females within their range. Males with no access to reproductive females had larger ranges than males with access to reproductive females. No difference in home range size could be found between the sexes breeding in grassland. Individuals tended to be territorial in both habitats. However, in the marsh, range overlap occurred between the peripheral areas of females and between males with no access to reproductive females. Increased density in grassland did not result in larger intrasexual overlap, but rather in smaller home ranges and larger intersexual overlap, although intersexual overlap was smaller when a male overlapped two females. The mating system varied from facultative monogamy in the grassland to polygyny in the marsh. During the nonreproductive period almost all animals were solitary and territorial, even during high density. It is suggested that burrows are the key resource for water voles living in habitats where individuals are highly exposed to Predation, resulting in different social systems between habitats.