Effect of resource abundance on woodland rodents' demography at latitudinal extremes in Europe

Climate change effects on primary productivity are especially evident along altitudinal and latitudinal gradients. Some of the species with a fast reproductive cycle strategy and relying on primary productivity may rapidly respond to such changes with alterations to demographic parameters. However, how these bottom-up effects may emerge in systems with different population dynamics has not been elucidated. We aimed to assess the role of food availability on rodent demography in populations characterised by different dynamics, that is multiannual cycles in Northern European populations and mast-driven outbreaks in Southern European populations, both driven by intrinsic and extrinsic factors. We live-trapped woodland rodents at these latitudinal extremes in two study systems (Norway, Italy) while deploying control/treatment designs of food manipulation providing ad libitum trophic resource availability, albeit not reflecting the natural resource fluctuations. We applied a multistate open robust design model to estimate population patterns and survival rates while controlling for seasonal variation, intrinsic traits, and co-occurrence of sympatric species. Yellow-necked and wood mouse (Apodemus spp.) were sympatric with bank vole (Clethrionomys glareolus) in Italy, while only the latter was trapped in Norway. Food provisioning increased both survival and population size of bank vole in Norway, where temperatures are harsher and snow cover persists in winter. In milder Italian habitats, the wood mouse abundance was boosted by food availability, increasing also survival rates (but only in females), whereas the bank vole showed a decrease in both parameters across sexes. We speculate that overabundant food resources may trigger some forms of competition between sympatric wood mouse and bank vole, although other types of interactions, such as predation and parasitism, may also contribute. By manipulating food availability in two systems where rodents have different population dynamics, we showed how resource availability exerted bottom-up effects on rodent demography, especially in the context of climate change, although being mediated by other intrinsic and extrinsic factors