Competition and the assembly of introduced bird communities

A central goal oi ecology is to understand what determines the number and identity of species in ecological communities. Of the many species that could potentially occupy an area, why do only a particular subset of species actually co-occur and what determines the identity of those species? And to what extent are these patterns the product of deterministic processes rather than stochastic events? Much interest has focused on interspecific competition as a process shaping cooccurrence patterns (Strong et al, 1984, Diamond and Case 1986): some species capable of joining a local community may be excluded by the presence of competitors. If competition is sufficiently strong and pervasive enough to structure ecological communities then certain 'assembly rules' should govern how communities are put together (Diamond 1975, Weiher and Keddy 1999). In particular, competition should be more intense, and competitive exclusion more likely, among species of similar size and morphology that compete for similar resources. In these circumstances we expect co-occurring species to be morphologically different from each other and to exhibit a pattern of 'morphological overdispersion' (Pimm 1991).