| Heterogeneity in herbivore density and feeding among plants is a ubiquitous feature of plant-herbivore systems. This variability has inspired generations of scientists, but modern ecology focuses on mean values of predictor and response variables. The result is that, for many ecological processes including herbivory, we have a poor understanding of the consequences of variability. This dissertation explores the consequences of heterogeneity in plants for the performance and behavior of individual herbivores, dynamics of herbivore populations, and patterns of plant-associated arthropod communities. Chapter one and two examine individual and population consequences of plant variability using Eutreta diana, a gall-making tephritid, on its host-plant, big sagebrush (Artemisia tridentata). Chapter one uses spatially explicit sampling to characterize spatiotemporal patterns of E. diana abundances. This chapter links those patterns to high heterogeneity in the strength of E. diana density-dependence among sagebrush individuals using a density-manipulation experiment in a natural population. Chapter two examines the relationship between the heterogeneity in E. diana density-dependence and E. diana oviposition behavior using a field experiment and laboratory behavioral assays. Chapter three reveals the influence of oak apple galls, formed by the California gall wasp (Andricus quercuscalifornicus), on the arthropod community on valley oak (Quercus lobata). This chapter uses a field experiment to show how heterogeneity in abundances of the gall wasp, mediated by plant quality differences, indirectly changes the structure of arthropod communities. Collectively, this work highlights the multi-scale ecological consequences of variability in plant traits. |
