The relative abundances of different species in natural plant communities is influenced by the outcome of competition among plant species and by herbivory, yet we lack a general understanding of how these forces interact in natural systems. In recent years, it has become increasingly clear that the spatial organization of species has a profound impact on how those species interact. The immobile nature of terrestrial plants makes plant competition a highly localized process. Damage by mobile herbivores, however, occurs over a regional scale. I will use spatially-explicit mathematical models, in conjunction with field experiments, to investigate the interplay between these local and regional processes in determining the composition and relative abundances of plant species in their natural habitats. The goldenrod beetle (genus Trirhabda) is known to reach extremely high population densities and to decimate its host plant, tall goldenrod (Solidago altissima). S. altissima is a competitive dominant, so this intense herbivory substantially reduces the competitive stress on other plant species, leading to dramatic changes in their abundances. I will use data on the Trirhabda-Solidago system to test the ability of my spatial models to explain patterns of abundances in natural plant populations. This work will comprise a unique examination of the role of spatial scale in shaping species interactions. By bringing together spatial ecological models and field data, my research will foster the development of mathematical methods that can be widely applied in the environmental sciences.
