Breeding suppression in voles under predation risk of small mustelids: laboratory or methodological artifact?

Many prey animals have life-history strategies that seem to have evolved to avoid predation from specialist predators. During the past few years, the hypothesis of breeding suppression (BSH) of voles as an adaptation to avoid small mustelid predation has prompted several empirical and theoretical studies. However, the validity of empirical work as well as justification of the conclusions in these studies have been criticised. Here we report results of an experiment in which we studied the breeding suppression of bank voles, Clethrionomys glareolus, in four replicated enclosures. We found no effects of simulated least weasel, Mustela nivalis nivalis. predation risk on the reproductive output of Female voles. In contrast to earlier laboratory studies, the weights of females did not differ between treatment groups after the experiment. We reanalysed results of our earlier laboratory studies in light of these results and criticism of the BSH. At present there is no direct evidence for breeding suppression of voles in field populations. Furthermore, the underlying assumptions of the BSH have not been tested experimentally. Thus the most parsimonious explanation for breeding suppression is that it may be a methodological or laboratory artifact.