UBC Theses and Dissertations

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UBC Theses and Dissertations

Algal-herbivore interactions in a high carbon world : direct and indirect effects through individuals, populations, and communities Anderson, Kathryn Michele


Consumer-resource interactions play an important role in determining the structure and function of ecological communities. Thus, herbivores may buffer or magnify the impacts of environmental change. In this thesis, I examine the ways in which herbivory mediates the effects of one of the most important facets of environmental change in marine ecosystems: ocean acidification (OA). Responses to OA by invertebrate herbivores are wide ranging, typically negative, and depend on species traits (e.g. reliance on calcification), population dynamics, and shifts in interspecific interactions. My goal was to conduct research across levels of biological organization to better understand the main pathways by which OA and associated increases in carbon dioxide (CO₂) will drive ecological change in herbivore-dominated systems. In Chapter 2, I examine the effect of CO₂ on herbivore growth and size-specific changes in feeding rate. I found that CO₂ had no impact on the size-specific feeding rates of the four-herbivore species I examined. However, changes in growth and body size in response to increased CO₂ may drive an overall reduction in the feeding rates of highly-calcified herbivores (e.g. urchins and gastropods), but not less calcified, crustacean herbivores. In Chapter 3, I used amphipod herbivores with short generation times to test the effects of CO₂ on per capita and abundance driven changes in herbivory. Again, I found no evidence for per capita changes in herbivory rate of this less calcified species, however increases in amphipod abundance lead to an increase in total herbivory. Finally, In Chapter 4, I manipulated both the abundance of gastropod herbivores and CO₂ in experimental tidepool communities in situ. I found that the indirect effects of CO₂ via the reduction of calcified herbivore pressure had a larger impact on tidepool community than CO₂ had directly. These results show that changes in herbivore pressure in response to OA will be driven primarily through changes in individual body size and herbivore abundance. Further, these changes in herbivory pressure can be more important in determining community structure under conditions of high CO₂ than other species-specific responses.

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