9528445 Osenberg The introduction of species outside their native ranges can provide unique opportunities to study the factors determining species distributions and abundances on both local and regional scales. Introductions of fishes into lakes are particularly useful because they resemble experiments; they are often replicated (introductions are made to multiple lakes), have controls (nearby lakes that did not receive introductions), and are often documented (recorded by agencies performing the introductions). For example, the redear sunfish (native to the southeastern US) is currently being introduced into Michigan lakes, where the pumpkinseed sunfish is native. The redear and pumpkinseed are similar in morphology and ecology (both feed primarily on snails), and are expected to compete strongly. Indeed, initial studies in Michigan suggest that pumpkinseed populations decline by 80% following redear introduction. The present research makes use of past and ongoing introductions of sunfish into Michigan lakes, coupled with comparative studies of sunfishes in the Carolinas (where both species are native), to explore the consequences of species introductions on native species, examine the causes of geographic distributions, and investigate some of the ecological mechanisms that drive these relationships. Species introductions are an increasingly common source of human impacts on natural systems, yet there is currently little ability to predict their impacts, mitigate their effects, or discriminate between introductions that have major effects and those that are relatively benign. This work attempts to integrate functional morphology, community ecology, and biogeography into a framework that can help resolve these shortcomings, and it addresses these issues in a group of economically and recreationally important fishes.
