Drivers of change in meso-carnivore distributions in a northern ecosystem
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- Institutt for biologi 
Species have been subject to major perturbations in recent times, such as over-harvest, habitat loss and climate change, affecting their distribution and abundance. Alpine and arctic tundra ecosystems are particularly vulnerable to such perturbations, where several species have experienced reduced distributions and population declines over the past century, affecting food web interactions and community structures. Underlying and potentially synergistic mechanisms driving these declines may concurrently facilitate invasions from neighboring ecosystems, increasing the pressure on tundra communities. In this thesis, I investigate the effect of perturbations on meso-carnivore communities within tundra ecosystems in Scandinavia, focusing on how climate change, anthropogenic impact and biotic interactions may drive diverging population trajectories of two competing meso-carnivores, the arctic fox and the red fox. Disentangling and quantifying these mechanisms are of fundamental importance for ecosystem-based management and in conserving threatened species. An initial retrospective analysis of meso-carnivore populations in Scandinavia over the past 150 years revealed complex synergistic mechanisms at several spatial and temporal scales driving the decline and non-recovery of the arctic fox whilst facilitating the expansion of red fox. By using extensive data from fieldwork-based studies paired with occupancy models and general linear models, I found that the more generalist and resource-limited red fox was favored by a milder climate and by anthropogenic impacts and was overall positively associated with larger tundra predators, likely due to resource provisioning. The arctic fox showed either a negative or no particular response to the same factors, whereas co-occurrence between red and arctic foxes shifted with availability of primary prey (small rodents). Relaxed climatic constraints and an increasing availability of resources will likely continue to facilitate the expansion of meso-carnivores such as the red fox, which necessitates ecosystem-based management encompassing resource availability and biotic interactions when conserving tundra communities and threatened species.