Thermal climate-linked variation in annual survival rate of hibernating rodents: shorter winter dormancy and lower survival in warmer climates

Abstract

In seasonal climates, many animals, including a wide range of small mammals, are physiologically capable of prolonged dormancy (˜hibernation), when foraging-related activity ceases entirely for part the year. Low metabolic rates while dormant minimise energy and water requirements, but the behavioural state of inactivity also reduces exposure to mortality risks, especially predation. Thermal effects on activity underlie spatial patterns in annual survival rate of ectothermic animals. We hypothesised that, because local thermal conditions affect the duration of mammalian hibernation, positive effects of dormancy on survival could also underlie a negative relationship between spatial variation in thermal climate and annual survival rate among populations of hibernating rodents. We applied mixed models to test for effects of local thermal climate on collated data of hibernation duration and annual survival rate among populations of hibernating and a representative sample of non-hibernating rodent species. Our analyses revealed strong negative effects of mean annual temperature on hibernation duration and adult annual survival rate within hibernating species (β: −8·6 day and −5·1% per 1 °C) but no effect in non-hibernating rodent species. This thermal climate-linked pattern in annual survival rate seems to be unique among mammals. A parsimonious explanation lies in the large increase in monthly survival rates during hibernation compared to activity. The current spatial pattern suggests ongoing climate warming might reduce annual survival rates of hibernating rodents by shortening their hibernation season. Decreased annual survival because of increased activity in warmer climates with shorter winter seasons is an unappreciated mechanism leading to impacts of global warming on animal populations in temperate climates.