Living in the edge: demographic responses driven by density-dependence and pulsed resources in a hibernating mammal

Populations at the edge of a species' distribution often encounter more challenging environmental conditions than those at the core, requiring unique adaptations and strategies. However, the demographic processes driving these populations remain poorly understood. This study aims to understand these processes and the population stability of the hibernating edible dormouse under challenging environmental conditions in two Iberian edge populations: Montseny and Montnegre. Despite their geographic proximity, Montnegre is demographically isolated and faces a harsher environment characterized by a drier climate and forests with lower deciduous tree diversity, whereas Montseny remains connected to other populations. Using long-term capture–recapture data, we analyzed the effects of density-dependence and seed availability on population growth, survival, and recruitment of dormice. Results indicated that both populations experienced large fluctuations in population growth rate, with a slight mean decline. Survival fluctuated less and was higher in Montseny than in Montnegre, likely reflecting the harsher conditions of the latter. We found a negative relationship between population size and both growth rate and survival in both populations especially in Montnegre, suggesting significant density-dependent effects that varied with stochastic annual seed abundance. This was likely influenced by the pulsed annual acorn production in Montnegre. Contrarily, high asynchrony between beechnut and acorn abundance in Montseny dampened the pulsed dynamics of seed availability. Interestingly, demographic contribution to population growth was dominated by survival in Montseny and by recruitment in Montnegre. When comparing survival rates with Central European core populations, we found that survival decreased with increasing climatic aridity, but was unrelated to proximity to the core, underscoring the role of spatial heterogeneity in habitat suitability, independent of range position. Our findings emphasize the complex interplay between ecological processes and evolutionary mechanisms at the edge of a species' range, highlighting the critical role of local adaptations and resource availability in shaping population dynamics.