I am investigating the effects of processes operating at different spatial scales on the number of species occupying local habitats. My most important discovery is that regional scale processes play profound role in shaping the structure of local species assemblages. This encourages me to think that appropriate explanations for differentially diverse communities must include biogeographic and evolutionary processes occurring over broad geographic areas as well as interactions within habitats. I am also working on the effects of invasive plant species on community structure and the effects of removing invaders on community recovery.