Environmental variability alters the relationship between richness and variability of community abundances in aquatic rock pool microcosms

The effect of species richness on the temporal variability of communities and populations continues to inspire investigations and debates; however, few empirical studies have addressed the crucial question of how the relationship between richness and variability changes along a gradient of environmental variability. We determined the relationship between species richness (S) and variability (coefficient of variation, CV) for both community and population abundances of aquatic invertebrates inhabiting 49 tropical coastal rock pools that differ in environmental variability. When all pools are considered, results support the hypothesis that variability in community abundance decreases with increases in species richness. In contrast, abundances of individual populations in more speciose communities vary no more than in species-poor communities. Richness-community variability relationships were detected in rock pools with low environmental variability (as measured by a multivariate index of environmental variability) and in rock pools with low variability in specific physicochemical variables, i.e., temperature, salinity, dissolved oxygen, and pH. The presence of richness-variability relationships in the less environmentally variable rock pools and not in the more variable rock pools suggests that environmental variability may play an important role in modulating richness-variability relationships.