Indirect effects in food webs at the Arctic's edge

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My research program examines indirect interactions in food webs to understand the mechanisms by which interactions between predators and their prey are affected by alternative food sources or other predators. This understanding will enhance the ability to predict how species loss or environmental change will affect ecosystem structure and dynamics. Arctic foxes are the main terrestrial predator throughout the Arctic; their primary year-round prey are lemmings, but they also feed extensively on migratory birds in summer and fall and consume seals on the sea ice in winter. They also impact other species by modifying the physical environment; through concentrating nutrients on dens, Arctic foxes enhance soil nutrients and increase plant productivity, which may attract lemmings and other herbivores. I am investigating indirect interactions involving Arctic foxes and their prey near Churchill, Manitoba, on the west edge of Hudson Bay, where boreal forest transitions to Arctic tundra. This site is near the southern edge of many Arctic species' distributions, where the impact of climate change is likely to be large. Declines in sea ice associated with climate warming are threatening polar bears, which provide Arctic foxes with access to seal carrion. The recent incursion of red foxes onto the tundra is another potential threat to Arctic foxes, which are smaller and may alter their den use and foraging patterns. I will train 13 students in the next grant cycle while addressing several short-term objectives. We will examine marine-based feeding by Arctic foxes and red foxes to determine if red foxes use tundra dens by the coast to access sea ice, thereby adopting the ecological niche of Arctic foxes. Using long-term harvest records we will assess fox population responses to changes in sea ice, snow, and other climate variables. We will also examine interspecific competition between Arctic foxes and red foxes by assessing overlap in diet and space use in response to varying prey availability, and investigate the chronology of tundra den occupancy by red foxes to determine if they usurp Arctic foxes or merely use unoccupied dens on the landscape. Changes in prey availability and predator pathogens may affect predation pressure on other prey species, so we will also examine these indirect effects by comparing annual variation in prey populations and viruses in each fox species. To assess impacts of ecosystem engineering by foxes we will examine lemming diets on fox dens, determine how fox dens promote shrub growth on upland tundra, and contrast the engineering effects on tundra and forest dens. Understanding indirect interactions among fox prey populations will help predict the wider consequences of climate change, and examining the importance of fox den sites for other organisms will reveal the broader impact of changes in fox populations at the southern edge of their distribution on Arctic biodiversity.