Contingency and the Impact of Ecosystem Engineers: The Role of Plant Traits

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Although all species modify their habitat in some fashion, the impact that 'ecosystem engineers' have on associated species has been quantified in only a few communities. The goal of this proposal is to quantify the relative influence of plant architecture versus leaf quality on the impact that leaf-tying caterpillars (engineers) have on the associated arthropod fauna of various oak (Quercus) species. In forming leaf ties, these caterpillars engineer a unique habitat that is colonized subsequently by other herbivore species, predators, parasitoids, and detritivores. By combining observation with experimentation, the investigator will test whether 1) the impact of engineers on a community depends on the suitability of the habitat for the engineer itself, 2) the magnitude of the engineering effect depends on the quality of the habitat engineered, 3) the impact of the engineer on species richness of the associated community depends on the relative number of species that are positively affected by the activities of the engineer, and 4) total arthropod species richness depends on interactions among generalist predators, species that specialize on leaf ties, and species that avoid leaf ties. This study will be one of the first to quantify the conditions that determine the impact an ecosystem engineer has on associated species and it will add to our limited understanding of the effects of invertebrate herbivores on their associated arthropod species, mediated through the host plant. The study will also be the first to quantify the relative importance of leaf quality and architecture for arthropod community structure. This study will clarify the role that insects play in forested ecosystems and their impact on forest productivity. In addition, it will identify plant traits that may provide resistance to initial attack by leaf-tying caterpillars. Information gained on the natural history of the arthropod species will be used in future illustrated guides developed for foresters, educators, and ecologists. Museum collections will be enhanced, both of the microlepidoptera and their parasitoids. Finally, the study will train a postdoctoral research associate, one graduate student, and a number of undergraduates in basic ecology and field research methods.