Ensamble de comunidades

Oecologia (2003) 136:489–498 DOI 10.1007/s00442-003-1311-7

REVIEW

Jonathan M. Chase

Community assembly: when should history matter?

Received: 31 December 2001 / Accepted: 12 May 2003 / Published online: 26 June 2003  Springer-Verlag 2003

Abstract Community assembly provides a conceptual foundation for understanding the processes that determine which and how many species live in aparticular locality. Evidence suggests that community assembly often leads to a single stable equilibrium, such that the conditions of the environment and interspecific interactions determine which species will exist there. In such cases, regions of local communities with similar environmental conditions should have similar community composition. Other evidence suggests that community assembly canlead to multiple stable equilibria. Thus, the resulting community depends on the assembly history, even when all species have access to the community. In these cases, a region of local communities with similar environmental conditions can be very dissimilar in their community composition. Both regional and local factors should determine the patterns by which communities assemble, and theresultant degree of similarity or dissimilarity among localities with similar environments. A single equilibrium in more likely to be realized in systems with small regional species pools, high rates of connectance, low productivity and high disturbance. Multiple stable equilibria are more likely in systems with large regional species pools, low rates of connectance, high productivity and low disturbance.I illustrate preliminary evidence for these predictions from an observational study of small pond communities, and show important effects on community similarity, as well as on local and regional species richness. Keywords Beta-diversity · Composition · Multiple stable equilibria · Ponds · Regional and local richness

Introduction
The processes that determine the patterns of the number andcomposition of co-occurring species have been central to community ecology for decades (Gleason 1927; Clements 1938; Samuels and Drake 1997; Belyea and Lancaster 1999; Weiher and Keddy 1999). In 1975, Jared Diamond proposed that community composition was characterized by a series of ‘Assembly Rules’, which could be predicted by a few key variables, such as the size of the species pool, the abioticenvironment, and interspecific interactions. However, in some cases, Diamond observed that community composition varied among sites that seemed similar in these key variables, and suggested that the timing of species invasions could lead to multiple stable equilibria (Diamond 1975). The pattern of community assembly remains controversial. One view holds that there is a one-to-one match betweenenvironment and community. In this case, regardless of the historical order in which species invade, if all species have access to a given community, composition should converge towards a single configuration in localities with similar environmental conditions. Communities that differ in environmental conditions, on the other hand, will have divergent community structure (Fig. 1a). Even when thehistory in which species invade a community is highly variable, theoretical models (e.g., Law and Morton 1996) and controlled experiments (e.g., Neill 1975; Tilman et al. 1986; Sommer 1991) often find little or no effect of history. The alternative view holds that different historical sequences of species entering a locality can lead to different final community composition, even when the environment ineach locality is similar and all species have access to the locality (Fig. 1b). This effect, known as multiple stable equilibria, can also be predicted from a variety of theoretical models (e.g., Luh and Pimm 1993; Law 1999) and has been found in several experiments (e.g., Robinson and Dickerson 1988; Drake 1991; Samuels and Drake 1997). Interestingly, the debate about community assembly dates...