UBC Theses and Dissertations

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UBC Theses and Dissertations

The impact of hyperabundant deer populations on bumblebees in the Salish Sea and decision options for deer management Beckett, Kephra


Garry oak and associated ecosystems (GOAE) are culturally and ecologically significant landscapes home to over 100 species-at-risk. Less than 5% of GOAE’s original extent remains in Canada, much of which is found on the Gulf Islands, within the Salish Sea of British Columbia. Due to reduced predation and hunting on the Gulf Islands, native black-tailed deer have become hyperabundant and are reshaping plant and animal communities. To guide the management, restoration and protection of these endangered ecosystems, this thesis examines the impacts of deer on a key group of native pollinators within GOAE, bumblebees. Globally bumblebees are in decline, and to date, the role of deer browsing in contributing to their decline has not been explored in GOAEs. I tested the hypothesis that deer browsing has an indirect impact on bumblebee populations through their direct negative impact on floral communities. I surveyed deer density, floral communities, and bumblebee abundances across ten islands with and without deer in the Salish Sea. I found that deer had a negative effect on the abundance of flowering plants, especially native species, and had an indirect negative impact on female bumblebees. These results clearly support the call for urgent deer management, so I then used these results in a structured decision making process to evaluate deer management options for the region. Following a structured decision process with 11 Garry oak ecosystem and deer experts we determined management objectives, management strategies, and the estimated benefit of each strategy. We developed 5 discrete strategies and 4 combinations of strategies to achieve different objectives – maximizing ecological integrity, maximizing the socio-political and technical feasibility of strategies, and minimizing costs. Results revealed that: 1) contract hunting had the highest estimated ecological benefit, 2) benefits were higher on smaller, less inhabited islands, and 3) birth control had the lowest estimated effectiveness. These results were used in tandem with estimated cost data to calculate final cost-effectiveness scores and prioritize the strategies. The top two cost-effective strategies were contract hunting, and the portfolio combination of contract hunting, Indigenous-led hunting, and improved predator viability, with estimated costs of $1.8Million and $2.3Million respectively.

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