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Low species diversity in the Arctic promotes strong food-web linkages, as changes in abundance of one species may influence many others. Using harvest records, I determined Arctic fox populations are declining in their southern distributional range due to shallower snow potentially limiting density of lemmings, their primary prey, which live and breed beneath snow. Additionally, warm fall and spring temperatures are shortening access to alternative prey, seals on sea ice. Arctic foxes also influence other species through non-trophic interactions, as lemming winter nests were found on 70% of fox dens examined. I determined warmer subnivean temperatures promoted by accumulation of thick snow leeward of tall vegetation on dens attracted lemmings to these dens. Furthermore, lemming reproduction was higher dens compared to traditional lemming habitat. This research highlights the impact of climatic variables on Arctic predator-prey interactions and the importance of understanding impacts of trophic and non-trophic interactions on species demographics. / February 2017

During the last 20 years studies of various mammals and birds have shown that social organization is highly variable between and within species, and that such variation can frequently be explained on the basis of variation in food habits and food dispersion. This study is an attempt to discover the major ecological pressures affecting social organization and reproductive fitness of Arctic foxes in Iceland. Foxes were both studied at an individual level, by monitoring movements of radio-tagged foxes and observation of fox behaviour in demarcated study areas, and at the population level, by analysis of available foxhunting records, as well as material and information provided by foxhunters. The most common form of social organization was found to be a breeding pair, while social groups of 3-4 individuals also occur, particularly in coastal habitat, which is more productive and spatially more heterogenous with respect to food dispersion, than inland habitat. The Arctic foxes were found to occupy well defined, but fairly flexible group territories, whose borders were advertised by olfactory, auditory and visual signals. In one coastal region, three such territories ranged in size from 8.6 km² to 18.5 km², while there was an indication that territories were larger in inland habitats. In coastal habitats, foxes feed mainly on oceanic prey and do not show cycles in abundance. In inland habitat, foxes show a functional response to the 10 year population cycle of ptarmigan (Lagopus mutus), their main prey in winter. Litter sizes remain stable, however, due to little interannual variation in the foxes' summer diet, which consists mostly of migrant birds. Mean litter size at birth is 5-3 ± 1.7 S.D. and mortality from factors other than foxhunting is about 15% up to the age of weaning. Annual mortality in adults is about 50%, mostly due to foxhunting. Most vixens breed already as yearlings, while dog-foxes are more likely to show delayed breeding. In inland habitats there is balanced polymorphism with regard to colour morph, but in coastal habitats blue foxes have an overall selective advantage. Inland foxes are smaller than coastal foxes. Both size and colour affect reproductive fitness.

I estimated the non-trophic effects of arctic fox (Vulpes lagopus) denning activities on soil nutrient dynamics, vegetation production and quality, snow cover thickness, and their primary terrestrial prey, collared lemmings (Dicrostonyx richardsoni), near Churchill, Manitoba in April, June and August 2014. Arctic foxes increased soil inorganic nitrogen and extractable phosphorous concentration on their dens. This increase in soil nutrient levels resulted in greater vegetation quantity (measured as biomass and cover) and quality (measured as nitrogen content) on dens. Increased vegetation cover, specifically Salix sp. and Leymus mollis cover, positively affected snow cover thickness on dens by trapping blowing snow. Increased snow cover thickness made dens attractive nesting sites to collared lemmings (measured as lemming nest counts). In addition, dens with lemming nests had greater snow cover thickness compared to dens without lemming nests. Greater vegetation quantity and quality on dens could also attract lemmings to dens for winter nesting. / February 2016

The occurrence and ecology of the apicomplexan parasite Toxoplasma gondii in arctic wildlife is not well understood. Transmission cycles, especially in terrestrial systems, are enigmatic because environmentally resistant oocysts, shed by felid definitive hosts, might be less responsible for transmission in the Arctic than in more southern latitudes. Toxoplasma gondii can also be transmitted through the food web by carnivory, and by transmission from mother to fetus during gestation, and these routes are thought to play a large role in the ecology of T. gondii in the Arctic. In this thesis, I examine T. gondii in a well-described part of the food web at Karrak Lake, Nunavut, in the central Canadian Arctic and through experimental infections of domestic waterfowl. In the field over 3 years, I sampled generalist carnovires (arctic foxes), migratory herbivores (Ross’s Geese and Lesser Snow Geese), and resident herbivores (lemmings). Using an occupancy modeling approach that accounted for imperfect detection, I compared commonly used serological assays to estimate prevalence of T. gondii antibodies in sera from arctic foxes and eluted blood on filter paper from Ross’s geese and Lesser Snow Geese and compared commonly used serological assays. I also used a naïve estimator to determine prevalence of T. gondii antibodies in sera from Ross’s Geese and Lesser Snow Geese, and blood on filter paper from lemmings. I detected antibodies against T. gondii in sera from arctic foxes (47-60%, depending on age category), Ross’s Geese (32%) and Lesser Snow Geese (28%). I also detected antibodies in blood on filter paper from Ross’s Geese (39% seropositive) and Lesser Snow Geese (36% seropositive) but not in lemmings. These findings suggest that light geese might introduce T. gondii to the Karrak Lake ecosystem with the annual spring migration and that oocyst transmission might not occur in the terrestrial system, because the parasite was not detected in resident rodents. For the in vivo experimental infections, we used a novel application of a multi-scale occupancy framework to determine within-host detection probability of T. gondii in experimentally inoculated domestic geese and then used those results to guide tissue sampling in wild Ross’s Geese and Lesser Snow Geese. In the experimental inoculation trial, the heart and brain had the highest detection probability for T. gondii through a real-time PCR with melt-curve analysis. Toxoplasma gondii DNA was not detected in tissues from wild geese, suggesting that the parasite was either not present, or methodological difficulties prevented its detection. The research presented in this thesis forms the groundwork for further T. gondii studies in this region.

Host behavior, age, sex, diet, and condition, as well as variation in parasite specificity, drive variation in parasite infection, and ultimately determine the host parasite community. The objectives of this thesis were to 1) examine intraspecific variation in arctic fox parasites, 2) determine relationships between diet and parasites in sympatric arctic and red fox, and 3) compare wolf parasites and diet. Male arctic fox had more cestodes than females and juveniles had more nematodes than adults, likely due to diet and exposure. Red fox carried fewer parasites than arctic fox, likely due to diet, evolved resistance behaviors and higher immune investment, but diet affected cestode abundance in both species. Wolves that ate more white-tailed deer had more cestodes, suggesting increasing deer populations could enhance parasite transmission to moose. However, body condition was unaffected by parasites, suggesting northern canids may have not reached a threshold of infection.

Host behavior, age, sex, diet, and condition, as well as variation in parasite specificity, drive variation in parasite infection, and ultimately determine the host parasite community. The objectives of this thesis were to 1) examine intraspecific variation in arctic fox parasites, 2) determine relationships between diet and parasites in sympatric arctic and red fox, and 3) compare wolf parasites and diet. Male arctic fox had more cestodes than females and juveniles had more nematodes than adults, likely due to diet and exposure. Red fox carried fewer parasites than arctic fox, likely due to diet, evolved resistance behaviors and higher immune investment, but diet affected cestode abundance in both species. Wolves that ate more white-tailed deer had more cestodes, suggesting increasing deer populations could enhance parasite transmission to moose. However, body condition was unaffected by parasites, suggesting northern canids may have not reached a threshold of infection.