Investigating the mechanism of Arctic fox (Vulpes lagopus) ecosystem engineering on dry heath communities in subarctic tundra

Arctic terrestrial ecosystems are some of the most extreme environments on earth, with a polar climate and landscapes recently carved by glacial retreat. Soil nutrient availability is a limiting factor for tundra productivity and under these conditions, the impacts of consumer-driven nutrient cycling can be magnified. Arctic foxes (Vulpes lagopus) are predators that act as ecosystem engineers in arctic and alpine tundra heath by altering the environment of their den sites, which exhibit increased soil nutrients, verdant atypical vegetation, and deeper snow. These fox dens are biogeochemical hotspots in otherwise nutrient-limited ecosystems and sources of cascading effects across trophic levels. It has been long hypothesized that these dens are so biotically productive because Arctic foxes increase the deposition rate of limiting nutrients by concentrating prey-derived nitrogen (N) and phosphorus (P) in the soil and this hypothesis has been descriptively supported but, the mechanism had not been confirmed with experimentation. To test the ability of the nutrients concentrated by Arctic foxes to cause the ecosystem effects observed on fox dens, I examined a long-term field experiment in Wapusk National Park. Vegetation plots received N and P additions (estimated from fox activity) and/or snow fencing on the windward side to increase snow depth. I investigated how the species composition of plot plant communities changed over 5 years, the treatment effects on plant productivity, intraspecific changes in prostrate shrub leaf metabolism, the response of resident insect communities, and the space use by collared lemmings. I found that nutrient addition facilitates the invasion of tall grass that can accumulate deep snow cover in the winter, deep snow can magnify some effects of increased nutrients, and the nutrient/snow combination can shape plant communities and create preferred lemming habitat. My thesis demonstrates how N and P deposition, increased to a rate within th