Understanding species abundances and distributions is a major goal of ecology. While manipulative experiments can reveal mechanistic properties of interactions among a small number of species, and macroecological studies can draw fundamental insights from patterns at a large scale, inference about local communities as a whole requires a combination of these approaches. I used a suite of techniques to better understand the ecological dynamics of a group of insect herbivores, the assemblage of moth caterpillars feeding on box elder, a common riparian tree. I examined the landscape ecology of the assemblage to determine the degree of turnover at multiple scales, and how diversity of the assemblage depended on host plant context. I found apparent homogeneity of caterpillar diversity masked important differences in co-occurrence even at small scales, though the expected influence of host plant diversity was not observed. Examining the species through time, I investigated how species abundance was related to body size, intrinsic population growth rate, and diet breadth. Whereas body size did not scale significantly with abundance in this group of species, and diet breadth had a complex relationship with abundance, the population growth rate developed in association with the host plant explained the differential abundance of species on the plant quite well. Finally, I quantified elemental content of species in the group, to determine how stoichiometric constraints related to size and growth rates of caterpillars in the assemblage. I found some support for a theory connecting elemental composition to ecological interactions, though the results were species-dependent. Throughout these investigations I explicitly considered the evolutionary relatedness of co-occurring species using phylogenetic methods. By merging ecological and phylogenetic data, a more unified picture of the important mechanisms underlying species properties can be obtained. Through tests of theory at the landscape, community, and individual level, I have presented a clearer picture of the forces structuring this assemblage of caterpillars, and provided a template for investigations of community dynamics at a similar scale.