UBC Theses and Dissertations
Nutrients in a changing world : the effects of warming and predator presence on prey quality Di Filippo, Carla
The field of climate change impacts on ecology primarily focuses on the measures of abundance and distribution of individuals to assess organism response, but the measure of organism quality is not often applied to assessing organism response within food webs. The abiotic factor of temperature has known effects on organism quality, but it is unclear how the biotic factor of predator presence impacts organism quality. The goal of my thesis was to investigate (a) the combined effects of warming and predator presence on prey nutrient quality, and (b) how temperature affects organism quality and the nutritional needs of consumers. To address the combined effects of warming and predator presence on one measure of prey quality - organism body size - I conducted a meta-analysis on 14 papers that tested both warming and predator presence on prey body size in aquatic systems. Across all studies, I found no net effect of warming on body size, a large increase in prey body size with predator presence, and an additive effect of the two factors combined. I then conducted a laboratory experiment using the primary producer Scenedesmus obliquus, the primary consumer Daphnia pulex, and the secondary consumer Chaoborus americanus to investigate temperature mediated changes in algal quality and consumer nutritional needs (measured using the fatty acid profile of algae that affected D. pulex population size and C. americanus growth rates). Overall, we observed changes in S. obliquus quality with temperature and mild cascading effects of these changes on D. pulex and C. americanus. Further investigation is needed into the effects of warming and predator presence on other nutrients (such as carbohydrates and proteins that may respond differently to temperature), and if the relationship between body size and quality holds true for all organisms. Overall, my thesis provides insight into how predator presence can have a stronger effect on organism body size than warming and suggests greater care must be taken when interpreting the results of studies that assess the effects of temperature on organism body size in the absence of biotic factors.
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