Date of Award

Winter 1994

Project Type


Program or Major


Degree Name

Doctor of Philosophy

First Advisor

Peter F Sale


The general aims of this research were to explore conflicting views of community structure and species introductions. In the former, I was interested in evaluating the relative importance of species interactions in determining their relative distribution and abundance. In the latter, my primary goal was to examine whether or not reported competitive dominance was a good predictor of either invasion mechanism or effect. As this research developed, an additional focus became the role of scale and methodology in determining how researchers perceive the effects of biological invasions.

Preliminary work (Chapter 1) took a broad approach, examining three species of sessile invertebrates, the ascidians Styela clava and Botrylloides diegensis as well as the ectoproct Membranipora membrancea. I documented changes in patterns of distribution and abundance, as well as competitive ability. I then used these results to make predictions as to the role of competition in mediating the establishment of these species at my study site as well as the likely long term effects of these introductions. Later work (Chapters 2 and 3) provide an in depth examination of one of the invasions outlined above; the invasion of the Great Bay Estuary by Botrylloides diegensis, focusing on interactions between this species and the closely related, and ecologically similar species Botryllus schlosseri. In particular, I utilized observational and experimental techniques to document distribution and abundance patterns of these species over four years at a number of study sites. In addition, I examined the potential role of interspecific presence in determining recruitment sites for larvae of both species. The thesis ends with a section which addresses the roles of scale and methodology in determining the apparent effects of biological invasions, and explores how these results relate to other issues of concern within the scientific community: particularly those of community structure.