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UBC Theses and Dissertations

Understanding drivers of caribou decline and feral horse dynamics in the Chilcotin Plateau of British Columbia Tjaden-McClement, Katherine G.


Understanding the complex mechanisms driving wildlife declines is crucial for effective conservation. In this thesis, I used camera traps to investigate two key conservation questions involving interspecies interactions in the Chilcotin Plateau of west-central British Columbia, Canada: 1) the role of disturbance- mediated apparent competition (DMAC) in the decline of the Itcha-Ilgachuz caribou population, and 2) the impacts of feral horses on native ungulate species. Caribou populations in Canada have faced significant declines, with DMAC emerging as an important contributor. I examined the mechanism of decline for the Itcha-Ilgachuz caribou, focusing on post- disturbance productivity, primary prey responses to disturbance, predator responses to prey and disturbance, and caribou overlap with predators and disturbance. I found a productivity pulse following disturbance, but low overall productivity. Primary prey exhibited strong preferences for burnt areas, but not cutblocks. Wolves were associated with primary prey, but not disturbances, and other predators showed associations with primary prey and/or disturbances. Caribou did not avoid cutblocks, potentially increasing their vulnerability to non-wolf predators. These findings provide mixed support for DMAC, and suggest that wildfire may be an important contributor to caribou decline in this population, emphasizing the importance of fire management going forward. I investigated the potential for competition between feral horses and two important native ungulates: moose and mule deer. Despite concerns about competition for wetlands and water resources, I found no strong evidence of competitive exclusion or avoidance by moose or mule deer in the presence of feral horses. While moose and feral horses shared a preference for wetlands, none of the species had increased use of areas near water sources. Although mule deer showed decreased use in areas overlapping with horses, this pattern was not conclusively linked to horse presence. These results suggest that feral horses may not be significantly impacting native ungulates in this region through competition, but further research is warranted to explore other impacts such as grazing and apparent competition. This research underscores the complexity and context-dependency of conservation challenges involving interacting species, emphasizing the need for management strategies informed by population-specific knowledge to effectively conserve threatened species and ecosystems.

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