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Beluga whales are year-round residents of the Arctic and top predators in the ecosystem. Many beluga whale populations are migratory and spend winters in polynyas and breaks in the ice to avoid entrapment. Once the ice in begins to break up and melt, beluga whale populations migrate to the same Arctic estuaries year after year. Possible uses of estuaries include feeding, aiding in skin sloughing, protection of calves from predators, and other warm water benefits. However, much is still unknown about the use of these habitats both spatially and ecologically. I investigated estuary use by Cumberland Sound beluga whales, through their distribution. Their summering area covers northern fiords of Cumberland Sound, including Clearwater Fiord where there is a large estuary. While the whales are known the frequent the fiords, the specific distribution and core areas were unknown. Using very high resolution satellite imagery, I established critical habitat within the summering region. I also provided an updated estuary abundance estimate for this small beluga whale population. Second, I explored estuary use of Hudson Bay beluga whales by investigating the primary feeding season. Migratory species often have one season where they eat the majority of their food for the year and build fat reserves, which provides energy and supports thermoregulation. This fat can be used to investigate feeding ecology of whales. Despite being the largest beluga population, fundamental ecological knowledge of Hudson Bay beluga whales, such as the primary feeding season is unknown. I used lipid content and adipocyte size throughout the blubber of Hudson Bay beluga whales to identify when they were consuming the majority of their food. I determined that there was no consistent primary feeding season, and therefore both summering and wintering areas were used for feeding. By exploring the beluga whales’ use of seasonal habitat through distribution and foraging ecology, my thesis illuminates fundame

Predators are widely recognized for their irreplaceable roles in influencing the abundance and traits of lower trophic levels. Yet, predators also shape community interactions and ecological processes via localized pathways, irrespective of their influence on prey density or behavior. I synthesized empirical and theoretical research and identified pathways by which predators have indirect ecological effects confined to discrete patches. This synthesis revealed how predators indirectly affect other species via patches – ranging from mediating scavenger interactions to influencing parasite/disease transmission risk – and ultimately provides a more holistic view of predation in ecosystems. I then demonstrated how satellite imagery could resolve whether Arctic foxes create biogeochemical hotspots via their denning behavior. Using satellite imagery, I showed that Arctic fox dens have greater plant productivity and green-up faster than reference sites, supporting the hypothesis that Arctic foxes cause the unique vegetation on their dens by concentrating nutrients derived from prey remains there. I then assessed how predators influence the reproductive ecology of Canada geese. Birds presumably select nest sites in areas they perceive are safer, but few links between spatial patterns of risk and nest habitat selection or nesting success exist. By comparing habitat selection models fit to goose nest locations and fox movement locations, I showed predator activity strongly affects the spatial distribution and reproductive success of geese. However, these effects were mediated by the date nest incubation started, revealing how nesting phenology and predator activity interact to shape bird reproduction. Finally, I assessed how fox predation affects goose reproductive success from an ecosystem-level perspective. I showed winter environmental conditions influence the abundance and availability of main winter foods for Arctic foxes, which in turn showed a numerical response to the

The loss and degradation of freshwater habitats in Canada threaten the rich array of plant and animal species supported within these ecosystems, threatening the biodiversity that these ecosystems sustain. Assessing the distribution of the species in these threatened ecosystems is necessary for the effective monitoring of the well-being of their populations and the ecosystem, but it can be difficult, as some species can evade traditional survey methods due to their elusiveness, size, range, or rarity. Environmental DNA (eDNA), which describes the pool of DNA present in an environment that can be collected in and isolated from environmental samples, offers an alternative to traditional surveying that can be more sensitive and less invasive. Therefore, I developed and validated TaqMan™ MGB probe-based eDNA assays for six freshwater fishes of conservation concern in Manitoba: Bigmouth Buffalo Ictiobus cyprinellus, Chestnut Lamprey Ichthyomyzon castaneus, Golden Redhorse Moxostoma erythrurum, Hornyhead Chub Nocomis biguttatus, Northern Brook Lamprey Ichthyomyzon fossor, and Silver Lamprey Ichthyomyzon unicuspis. The designed assays were validated in situ using paired eDNA and capture-based sampling and used to map the distribution of the above species from water samples collected and filtered from 129 sites across Manitoba in 2021–2023. I detected the eDNA of four of the target species outside of their historic range: Bigmouth Buffalo in the Roseau, Morris, and Assiniboine rivers; Golden Redhorse in Hazel Creek; Hornyhead Chub in waterbodies of the Winnipeg River watershed where it has not been reported previously; and Northern Brook Lamprey in Boggy River. Apart from Northern Brook Lamprey, the eDNA of all target species was not detected in at least one site within their historic range. Further research is needed to confirm if the lack of eDNA detections of the target species within their historic range is a result of range restriction, or if a refinement of the methods

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