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RESEARCH PRODUCT

Phenotypic Flexibility in the Social Organization of Clethrionomys

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I review the flexibility of social organization and spacing behavior in Clethrionomys. This review is based on a 6-year comparative study and several experimental studies on cyclic populations of the bank vole, C. glareolus, in Central Finland. The social organization of Clethrionomys populations shows great flexibility during both the breeding and nonbreeding season, and is dependent on habitat patchiness, food availability, Predation, kinship, philopatry, and familiarity between individuals. The first three factors are most important in destabilizing a population, whereas the last three stabilize a population without exhausting its resources. Female territoriality can weaken in a productive environment perhaps due to increasing kinship between reproductive females during the breeding season. During the winter, food availability seems to determine the social structure of the population, which consists of either large or small aggregations of both sexes. Winter territoriality may be influenced by relatively homogenous habitat with low productivity. Forest-dwelling species of Clethrionomys seem to adopt behavioral tactics different from those of most Microtus that live in a productive, but unstable habitat. Despite these behavioral differences, both genera cycle synchronously in northern Fennoscandia. This leads to the conclusion that we have to seek explanations for microtine cycles not based on the behavior of individual voles.