Affiliation: College of Arts and Sciences, Department of Biology
Temperature can affect population and community level processes, via strong and predictable effects on individual metabolism. Metabolic Scaling Theory (MST) 1) describes how individual metabolic rates scale with temperature, and 2) generates mechanistic predictions based on how this response to temperature variation will drive ecological pattern and process. For example, temperature can influence trophic interactions via differential metabolic scaling of predator and prey metabolic rates. More specifically, metabolic theory and experiments indicate warmer temperatures can increase the top-down effects of herbivores on plant biomass, resulting in depleted standing plant biomass. Yet there are few studies that have tested metabolic scaling theory in the ocean across natural, in situ, environmental gradients. The Galapagos Islands is the ideal system for testing metabolic scaling theory in situ because the Archipelago is at the center of several different oceanographic currents (tropical, subtropical and upwelled water), resulting in enormous variation in water temperature (11°C - 31°C). Upwelling is the wind-driven process of cold, nutrient-rich subsurface water replacing warm, nutrient-poor surface water. Also, even though community composition differs across the Archipelago due to oceanographic conditions, there is a suite of organisms that are present across the Islands throughout the year. For my doctoral dissertation research, I quantified benthic community patterns across the Islands and related community composition and biomass to temperature. I also tested metabolic scaling theory in the Galapagos Islands via lab experiments, in situ grazing assays, and a long-term exclusion experiment. Further, to examine the generality of temperature variation in upwelling systems, I analyzed in situ temperature data from five upwelling regions and examined differences in thermal regimes between the regions. I then related this temperature variation to local grazer-algal interactions. Overall, my findings provide evidence for a mechanistic link between temperature and grazing rates and suggest temperature-mediated herbivory could be important in influencing benthic community patterns in upwelling systems.