| Ecological character displacement, or trait evolution stemming from resource competition, occurs when selection to avoid resource competition favors individuals of two competing species who are least like the other species in resource use traits. Character displacement is an important mechanism driving adaptive radiation and species coexistence, and it has been documented in many taxa. Yet, many factors that affect the evolution of character displacement and its consequences remain unclear. My dissertation research seeks to address this gap.;Character displacement may evolve through two non-exclusive routes that differ in the source of phenotypic variation, and hence, in the ease with which character displacement unfolds. I discuss differences between these routes, review possible examples of each, and describe how distinguishing between them provides insight into factors that affect the evolution of character displacement and its possible consequences.;When resources are asymmetric, character displacement may lead to differential fitness consequences between competing species, creating a "winner" and a "loser." Using population genetics, I established that the winner in a case study of character displacement---spadefoot toads---was the more recent invader into the region where character displacement has occurred. I suggest that because superior competitive abilities may facilitate invasions, invaders may generally win during character displacement.;In putative cases of character displacement, it is important to establish that selection, and not chance, has been primarily responsible for generating trait divergence. One way to do this is to demonstrate that multiple populations have diverged independently. Using a population genetics approach, I found that multiple sympatric populations of the spadefoot toad Spea multiplicata have independently diverged from allopatric populations. In addition to supporting the role of selection in this case of character displacement, my results also clarify by which route this species underwent character displacement.;Finally, an indirect consequence of character displacement is that it may initiate speciation between conspecific populations experiencing different competitive environments. With genetic data, I found evidence of a slight reduction in gene flow between S. multiplicata populations in different competitive environments. These data therefore support the suggestion that speciation may arise as an indirect consequence of character displacement. |
