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UBC Theses and Dissertations

Community ecology in a warmer world : direct and indirect effects of temperature on community dynamics Kordas, Rebecca Lee


As the Earth’s climate changes so too do its ecosystems, due to shifts in abundance, biodiversity and interaction strengths among their constituent species. Although warming will simultaneously affect many aspects of ecological communities, disentangling the abiotic and biotic contributions will improve our understanding of how assemblages of interacting species will respond to climate change. My goal was to determine how warming affects community assemblages via direct (mediated by organismal physiology) vs. indirect effects (mediated by species interactions). I addressed this with 12-16 month-long manipulative experiments in the rocky intertidal zone of Salt Spring Island, Canada. I created a novel in situ method for increasing substratum temperature for settling benthic organisms, using black- and white-bordered settlement plates. In the first experiment (Chapter 3), I monitored the response of functional groups and diversity to warmed treatments. Results from this experiment suggest that communities in thermally stressful habitats respond to warming via the interplay between species-specific physiological responses and secondary adaptive strategies such as behavioral microhabitat selection. In Chapter 4, I concentrated on the direct effects of warming. As a case study, I monitored the direct effects of in situ warming on the vital rates of two competing barnacle species. Warming negatively affected both species of barnacles, however the population of the competitive dominant was more severely affected than the subordinate species, leading to a temperature-induced change in space occupancy. In Chapter 5, I focused on the indirect effects of warming on community dynamics by manipulating temperature and herbivore access to communities. Community structure and successional trajectory differed markedly between treatments, due to disturbance from herbivores and high species turnover due to warming. Despite the stochastic nature of development, warmed communities with herbivores ultimately lost the variability created by herbivore-associated disturbances, resulting in highly similar assemblages between warm and cool treatments. These results illustrate how environmental change can alter species-specific thermal responses, complex population dynamics, and interaction strengths, with cascading impacts on community dynamics. They further demonstrate how assemblages of multiple, interacting species will respond to climate change, which is imperative if we hope to effectively prepare for and adapt to its effects.

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