| It is well established that phenotypic variation can alter the nature of ecological interactions by modifying interaction strengths and that ecological interactions can shape phenotypes by molding the forces of natural selection. An emerging area of research seeks to unify these concepts in order to understand how ecological and evolutionary forces, together, shape the origin and maintenance of functional biodiversity, or that component of biological variation that determines community and ecosystem processes. In this dissertation, I explored the causes and consequences of eco-evolutionary interactions in two systems, islands and lakes, to attempt to understand how ecology and evolution interact in natural ecosystems.;First, I re-examined the island rule of vertebrate body size evolution by combining traditional ecological explanations based on changes in predation pressure and resource availability with modern life history theory. I found this approach to be consistent with the available data and more generally applicable than previous explanations based on ecological interactions alone.;Second, I examined the ecology and evolution of alewife (Alosa pseudoharengus) populations and zooplankton communities in Connecticut (USA) lakes to determine whether eco-evolutionary feedbacks have shaped phenotypic traits and ecological interactions. I measured foraging traits and diets in anadromous and landlocked (freshwater resident) alewife populations, and determined that these populations have diverged in gape width, gill raker spacing, prey size, and prey selectivity. Differences in zooplankton dynamics, shaped by differences in the timing and duration of alewife predation, appear to underlie this phenotypic divergence. I used a mesocosm experiment to reveal that trait differences, in turn, drive differences in mid-summer zooplankton community structure.;Finally, I used mtDNA and microsatellite data to examine the pattern and rate of evolution in Connecticut alewife populations. This analysis revealed that landlocked populations have evolved multiple times from an anadromous ancestor. Divergence time estimates suggested that landlocked populations probably evolved as a result of Colonial dam construction. Rapid evolution is likely to facilitate eco-evolutionary feedbacks, and the rate of evolution for alewife foraging traits was determined to be equal to other demonstrated cases of rapid evolution. |
