Author: Lewthwaite, Jayme
Species' responses to anthropogenic have been varied and complex. Some species and areas have flourished, whilst others have been reduced to a fraction of their previous extent or diversity levels. Are these responses idiosyncratic or are there generalizable patterns that we can extract in order to prevent further losses of biodiversity by prioritizing those species that require it most? I examine spatial and temporal responses of approximately 300 species of Canadian butterflies over the past century over a wide spatial and environmental gradient. I test whether species' intrinsic biology as well as the magnitude and direction of both climate and land use change have dictated biological responses at 3 levels: species, community and phylogenetic. I find that range size emerges as the most important predictor of a species' ability to track climate change at its' northern range margin. It is also the most important predictor of a species' ability to both colonize a new quadrat as well as their likelihood of being extirpated from another. Additionally, I find that climate change as well as land use change have played a significant role in shaping those community responses. Specifically, agricultural development and climate change have resulted in an overall decline in species richness and a concurrent phylogenetic overdispersion of community members. Meanwhile, agricultural abandonment has resulted in net gains in species richness, though the species that are added tend to be close relatives of those already present. Altogether, these responses have had a homogenizing effect on the geography of Canadian butterfly diversity, and the corresponding impact of these changes on abundance remains unknown. These results may help resolve the recent discrepancy between global and local diversity trends (no net change vs an extinction crisis). Although I found that species richness has, on average, slightly increased within a quadrat, this masks a variety of other more nuanced changes in community composition and phylogenetic structure. These results do not negate other widely-documented insect declines. Rather, they underscore the importance of studying multiple axes of biodiversity change in order to get a complete picture of responses. Finally, alternative strategies, such as phenological shifts, may offset the lack of observed range shifts in many Canadian butterfly species. The potential simultaneous retraction at Southern range margins, however, may further endanger these species. Future studies should focus on layering these responses on to what has already been found in order to get a complete picture how and why Canadian diversity has and will continue to change into the Anthropocene.
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Thesis advisor: Mooers, Arne
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