Lake Food Web Responses Across Environmental Gradients
This PhD thesis incorporates environmental conditions into notions about what mediates the structure of major trophic pathways and the biomass structure of food webs. The result is a set of new ideas that extend understanding of how changes in environmental conditions impact the structure of food webs. Unlike many traditional studies that present binary, static food webs in a homogenous environment, here I consider changes in relative trophic interaction strengths and make simple spatial arguments about habitat differences to link food web structural shifts to environmental conditions (for example, ecosystem size, climate, and visibility). I argue that the adjustments organisms make to avoid, or to exploit, the mosaic environment regulates the major trophic pathways that fuel whole food webs. I develop a set of theoretical predictions and use literature data and a substantial new dataset that I have assembled from Canadian lakes to show that trophic pathways can vary in predictable ways across environmental gradients. These findings provide new insight into an emerging research area that asks how the environment determines the macroscopic properties of food webs. Furthermore, this research provides new knowledge on Canadian freshwater lakes which house a significant portion of the world’s freshwater life, as well as, socially and economically important fisheries. I discuss the potential implications of the food web structural changes documented for the persistence of species in natural systems. Since many organisms experience the world as an environmental mosaic, and humans act to modify this natural variety, changes in key food web structures across important environmental gradients provide an initial understanding of some of the changes ongoing as contemporary ecosystems face unprecedented change.