The effects of seasonality on variation in the length of breeding season in arvicoline rodents

Strong seasonality, coupled with long winters, has increasingly been propos ed as a causal factor destabilising population dynamics in arvicolines. How ever, there are few empirical data demonstrating geographic variation in th e length of breeding season with respect to seasonality In 78 populations o f 24 vole species living in both Eurasia and North America, I explored the responses to seasonality (defined as annual temperature amplitude), maximum monthly average temperature, minimum monthly average temperature and three geographic variables represented by latitude, altitude and distance to the nearest seacoast. I assessed their effects at the level of (1) populations , by fitting generalised linear mixed models, and (2) species, by fitting s tandard linear models using both species means and phylogenetic independent contrasts. Populations in more seasonal environments exhibited shorter bre eding seasons but the predictive power of minimum temperature was greater b y far than that of temperature amplitude. The stronger seasonality in North America did not translate into shorter breeding seasons in North American arvicolines. The results indicated that annual temperature range and minimu m temperature, when used as correlates of density dependence, could be of h elp in disentangling the potential effects of seasonality and length of bre eding season on population dynamics in microtines.