THE STATISTICAL INEVITABILITY OF STABILITY-DIVERSITY RELATIONSHIPS INCOMMUNITY ECOLOGY

In this article, we explain an often overlooked process that may signi ficantly contribute to positive correlations between measures of speci es diversity-and community stability. Empirical studies showing positi ve stability-diversity relationships have, for the most part, used a s ingle class of stability (or, more accurately, instability) measures: the temporal variation in aggregate community properties such as bioma ss or productivity. We show that for these measures, stability will es sentially always rise with species diversity because of the statistica l averaging of the fluctuations in species' abundances. This simple pr obabilistic process will operate in the absence of any strong species interactions, although its strength is driven by the relative abundanc es of species, as well as by the existence of positive or negative cor relations in the fluctuations of species. To explore the possible impo rtance of this effect in real communities, we fit a simple simulation model to Tilman's grassland community. Our results indicate that stati stical averaging might play a substantial role in explaining stability -diversity correlations for this and other systems. Models of statisti cal averaging can serve as a useful baseline for predictions of commun ity stability, to which the influences of both negative and positive s pecies interactions may then be added and tested.