Interspecific competition between mice and voles induced by ad libitum food resources: a simulation of climate change effects on sympatric species?

How resources are partitioned among sympatric species is conditional to extrinsic (e.g. climate driven) and intrinsic (e.g. demography-dependent) factors. To analyse these effects, we carried out a treatment-control experiment with supplemental ad libitum food accessible to the community of wild rodents, throughout seasons at two latitudinal extremes. We intensively live-trapped woodland rodents in north-eastern Italian Alps (2019 – 2021) and in south-eastern Norway (2013 – 2015), and applied multistate open robust design models to estimate the variability of demographic parameters under the experimental settings. Rodent assemblage was different at the two latitudes, with yellow-necked mouse, wood mouse (Apodemus spp.) and bank vole (Myodes glareolus) living in sympatry in Italy, whereas only bank vole occurred in Norway. In Norway, food scarcity and harsh climate seemed to limit rodent survival and abundance. In Italy, supplemental food promoted mice abundance, which in turn seemed to depress voles survival and abundance, most likely due to inter-specific behavioural and exploitative competition. The competitive mechanisms which we induced by providing ad libitum food resources may simulate population responses under climate change scenarios, with generalist species (e.g. Muridae) becoming prevalent part of the assemblage and overriding specialist species (e.g. Arvicolinae), also at the current extremes of their distribution range.