Demographic effects of climate fluctuations on an alpine marmot (Marmota marmota) population [Effets démographiques des fluctuations climatiques sur une population de marmotte alpine (Marmota marmota)].

Résumé

Climate shapes demographic rates of a wide range of large herbivore species. The underlying processes most frequently advanced are a variation of resource abundance and a quality with precipitation or temperature and the costs of locomotion in snow during winter. Alpine marmot copes with winter by overwintering in burrows (from September to late April) so that consequences of climate maybe less marked than for non-dormant species. We predicted marmot survival and recruitment to depend primarily on summer condition before wintering when they build fat body reserves and less on winter condition. We found that survival of all age- and sex-classes of marmots responded to climate. In summertime, the amount of rain per month was negatively associated with marmot survival. Moreover, winter condition was also important to marmot survival. The average thickness and the extent to which the snow layer lasted in spring were significantly correlated to marmot survival. In contradiction with the current view of climate effects in herbivore populations, summer precipitation decreased survival despite it is generally reported to increase the primary production. We discuss this relationship in terms of too high costs of thermoregulation when foraging under wet conditions. Thermoregulation was also important in winter since the snow layer thickness, acting as an insulation layer, decreased the probability of survival when too thin. Our results suggest that thermoregulation is a key factor in alpine marmot and provide some insights regarding the consequences of climate change on this species.