Ecological and Evolutionary Consequences of Herbivory on Plant Communities

Understanding the consequences of species interactions is central to ecological and evolutionary research. My research focused on better understanding the evolutionary ecology of plant- herbivore interactions by asking two broad questions: 1) How do herbivores shape the composition and diversity of plant populations and communities? And, 2) How does genetic variation and ongoing evolutionary dynamics in herbivores influence plant ecology? To test the first question, I utilized long-term herbivore manipulations in the grasslands of Silwood Park, England. I tested ecological and evolutionary consequences of rabbit (Oryctolagus cuniculus) grazing on plant populations by collecting seeds from rabbit exclosures ranging in age from 4 months to >20 years and growing them in common environments. I found that rabbit exclusion caused evolution of multiple plant defensive traits in three plant species and influenced the costs and benefits of a mutualistic interaction between a grass and its fungal endophyte. In another experiment at Silwood Park I investigated how multiple groups of herbivores (rabbits, insects, and mollusks) and nutrient additions shaped plant species richness and phylogenetic diversity. I found that nitrogen addition strongly reduced species richness while rabbit grazing increased plant phylogenetic diversity. To test the second question, I conducted field experiments where I manipulated the genotypic composition of green peach aphid (Myzus persicae) populations on two host plant species. I found that genetic variation in M. persicae had large impacts on plant growth, that M. persicae populations changed in genotype frequency (i.e. they evolved) over 5 generations, and that in some cases faster evolving populations had larger negative impacts on plant growth. Together these results demonstrate how herbivory can concurrently shape the ecology and evolution of plants at multiple levels of organization and that herbivore genetic variation and evolution can have important consequences on plant ecology.Ph.D