Evolution of the trophic niche and food web structure

Food webs – networks of predator-prey interactions – are of fundamental importance to the ecological and evolutionary dynamics of biodiversity. The stability and functioning of food webs can be dependent on their 'vertical' structure: the distribution of species' trophic positions, the length of food chains and the prevalence of omnivory. Food web interactions such as predation, resource competition and intraguild predation can be potent agents of natural selection, driving evolutionary responses that feed back to reconfigure the food web. The structure and function of food webs thus arises from an interplay of ecological and evolutionary processes. My thesis describes four studies of the evolutionary ecology of food webs. First, I test whether trophic position evolution is associated with speciation events in Sebastes rockfish. My phylogenetic comparative analyses find no signal of change at speciation in the evolution of trophic position or trophic morphology. Instead, speciation events in rockfish appear to be primarily associated with divergence in depth habitat in the ocean. Next, I use an evolutionary assembly model to explore how the strength of foraging trade-offs influences the structure and temporal dynamics of food webs, as well as patterns of trait evolution. Across a range of trade-off strengths, the amount of omnivory in a food web is positively related to both species turnover and the degree of convergence in trophic position evolution. I then fit macroevolutionary models to Sebastes trophic position data. The data support a model of recurrent evolution in a constrained trait space, as predicted for omnivorous consumers. Finally, I examine the ecological and evolutionary consequences of intraguild predation on three spine stickleback (Gasterosteus aculeatus) by prickly sculpin (Cottus asper). My collaborators and I use comparative and experimental studies to show that sculpin presence in lakes is associated with the evolution of antipredator and pelagic foraging morphology in stickleback, leading to reduced predator vulnerability, increased zooplanktivory, and changes to the structure of the food web. These studies address a number of important questions about how evolutionary processes influence food web structure and function, and illustrate the work that remains to be done in this exciting area of research.Science, Faculty ofZoology, Department ofGraduat