At the heart of my interests is the problem of how ecology and evolution combine to determine the number and abundances of species in communities. I have approa ched this subject from two relatively different angles, although I am always trying to hook the two back together.

In community ecology, I have been interested in the role and evolution of indirect effects and in the relative importance of immigration, species interactions, local adaptation, and chance in determining community structure. Indirect effects among competitors have been of particular interest to me because they tend to be facilitative (Miller, 1994), which has important implications for diversity and stability of communities and the evolution of species in those communities (Miller and Travis, 1996). I am continuing this work using models of evolution in entire communities and with experimental studies with the invertebrate communities that live inside leaves of the pitcher plant Sarracenia purpurea (Harvey and Miller, 1996; Miller et al., 1994).

In plant evolutionary biology, I started with an interest in how competitive ability evolves in plant populations. We have demonstrated heritable variation in competitive ability in Brassica rapa and that competitive ability in intraspecific competition can be quite similar to that in interspecific competition (Miller and Schemske, 1990; Miller, 1996). We have extended this work to explore the mechanisms by which increasing density affects fitness variation within the population and subsequently how this fitness variation translates into different fitness and selection (Miller, Winn, and Schemske, 1994; Winn and Miller, 1995). I have also been interested in how the selection intensity that results from any one environmental "force" (e.g., competition, herbivory, drought stress) is affected by the presence of a second environmental force. I developed a theoretical prediction that such interactions would generally increase selection intensity, depending on the correlation between the occurrences of the two forces. I have now tested this prediction using competition and "artificial" herbivory on Rapahanus raphanistrum: the predictions seems to hold for some, but not all, traits. I am still analyzing the data in an attempt to understand this partial support of the theory.