Predation risk and reproduction in the bank vole

Abstract

Context Life-history strategies are the means that organisms use to achieve successful reproduction in environments that vary in time and space. Individual animals maximise life-time reproductive success (LRS) through optimal timing of reproduction and investment in offspring. A crucial factor affecting LRS is predation risk in a highly seasonal environment. According to the breeding-suppression hypothesis (BSH), females should delay breeding under short periods of high predation risk. Delayed breeding under risk is suggested to have substantial consequences for females’ fitness. Aims We tested the BSH in an iteroparous boreal small rodent, the bank vole, Myodes glareolus. Methods We used caged-live weasels and spread weasel scent to simulate increased predation risk in four of eight 0.25-ha outdoor enclosures. We monitored females’ reproduction in three periods (May, July, August), i.e. during the breeding season over the course of summer. Key results Contrary to our main prediction, predation risk did not affect timing of mating, pregnancy rate or litter size in any study period. Conclusions and implications We conclude that during the short but resource-rich breeding season of boreal summer, postponing breeding does not seem to be an optimal strategy for females, even under high risk of predation. Under favourable summer condition, i.e. in circumstances without any constraining factors such as food or conspecific density, females manage to balance the costs of predation against benefits of resource availability and do not suppress breeding. Although the BSH has been studied widely, also our results reveal the intricacies of this adaptive behaviour.