BREEDING SUPPRESSION IN THE BANK VOLE AS ANTIPREDATORY ADAPTATION IN A PREDICTABLE ENVIRONMENT

In northern Fennoscandia, microtine rodent populations fluctuate cycli cally. The environment of an individual vole can be considered to be p redictable when the risks of predation and intra- and interspecific co mpetition change with the cycle, such that both are high during the po pulation highs of voles. The risk of predation is also high during the vole crash. After the crash, the vole population is characterized by low intra- and interspecific competition and low predation pressure. T he main predators affecting voles during the crash are the small muste lids, least weasel and stoat. The density of these specialist predator s declines drastically during the winter after the vole crash. We stud ied experimentally the impact of the perceived presence of stoats on t he breeding and mating behaviour of voles. In a series of breeding exp eriments with bank voles, Clethrionomys glareolus, both old and young females suppressed breeding when exposed to the odour of stoats, Muste la erminea. The weights of females decreased in both experimental and control groups, but more among the voles under odour exposition. It se ems that females actively avoided copulations under high predation ris k and that breeding suppression is mediated by a change in female mati ng behaviour. There was no change in male behaviour or physical condit ion between the experimental and control treatments. An alternative me chanism for the observed breeding suppression could be the one caused by decreased feeding in females mediated with low energy intake which does not allow breeding. Regardless of its mechanism, delay of breedin g should increase the probability of non-breeding females to survive t o the next breeding season. The females surviving the crash should gai n a strong selective advantage in a predator-free environment of the s ubsequent breeding season, which could explain the adaptive function o f this antipredatory strategy.