The evolution of life history strategies therefore is constrained along a slow–fast continuum, in which species with slow life histories generally have higher survival rates, live longer maximum life spans, mature at older ages and produce fewer young per year compared with species with fast life histories. Moreover, in stable populations, survival and birth rates must be inversely related. With limited resources, an organism cannot simultaneously maximize both of these traits but must balance investment in survival versus offspring to maximize its lifetime reproductive fitness. The existence of a trade-off between lifespan and reproduction is central to the concept of an evolved life history strategy. Thus, our combined results suggest that (i) hibernation is associated with high rates of overwinter and annual survival, and (ii) an increase in survival in hibernating species is linked with the coevolution of traits indicative of relatively slow life histories. In accordance with evolutionary theories, however, hibernating species do not have longer life spans than non-hibernators with similar survival rates, nor do they have lower reproductive rates than non-hibernators with similar maximum life spans. As predicted, we found an effect of hibernation on the relationships between life history attributes and body mass: small hibernating mammals generally have longer maximum life spans (50% greater for a 50 g species), reproduce at slower rates, mature at older ages and have longer generation times compared with similar-sized non-hibernators. Hibernators also have approximately 15 per cent higher annual survival than similar sized non-hibernating species. Monthly survival was in most cases higher during hibernation compared with the active season, probably because inactivity minimizes predation. We used phylogenetically informed GLS models to test for an effect of hibernation on seasonal and annual survival, and on key attributes of life histories among mammals. Hibernation allows a diverse range of small mammals to exhibit seasonal dormancy, which might increase survival and consequently be associated with relatively slow life histories. Survival probability is predicted to underlie the evolution of life histories along a slow–fast continuum.
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