DISSERTATION RESEARCH: Spatial Scale and Population Persistence: Insights from a Plant-Herbivore-Parasitoid System

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962301 Frank This research focuses on how populations persist in nature. This goal is pursued in two ways: (1) Investigations of dynamics within local populations to identify factors that may stabilize population fluctuations, and (2) investigations on a broader spatial scale to determine whether interactions among local populations can bring about regional persistence. This study system consists of the harlequin bug (Murgantia histrionica), a herbivore on bladderpod (Isomeris arborea), and two parasitoids that attack bug eggs. Patchy distribution of the host plant clearly delineates the units on which local and regional dynamics will be investigated. On the local scale, parasitoid exclusion experiments will be conducted to determine whether the presence of two asynchronously acting parasitoids leads to host population stability. On the regional scale, host and parasitoid dispersal will be manipulated in experimental archipelagoes to determine whether dispersal among local populations leads to regional stability. Dispersal manipulations will be complemented by examination of distance and density-dependent effects of dispersal, and by empirical and theoretical explorations of how interactions among dispersal and environmental heterogeneity influence asynchrony among local populations. The results of this study will be important for several reasons. First, there is much current interest in the dynamics of subdivided populations that are interconnected by dispersal because of the practical implications for habitat fragmentation and conservation. Second, the choice of study system allows investigations of how habitat patchiness influences the interactions among species and the community-level processes that affect extinctions. Multi-species interactions in a spatially subdivided setting can also provide insights into biological control of insect pests. Understanding how complex species interactions persist in subdivided habitats is perhaps the most important issue for the science of con servation biology.