Physical determinants of richness, diversity, evenness and abundance in natural aquatic microcosms

Histories, biotic factors and abiotic factors interact to determine biodiversity. A comparison of systems formed over a range of physical conditions may help to evaluate the role of physical factors in determining community structure. We investigated abiotic determinants of species richness, abundance, biomass, diversity and evenness using a series of erosional rock pools on the northern coast of Jamaica. Aquatic invertebrate community data were collected from 1989 to 1997, along with repeated measurements of physical variables, including descriptors of pool conditions, morphometric characteristics and other derived measures to a total of 17 variables. These variables were used to evaluate a range of regression models, from simple to complex, which explained the observed biodiversity. Simple regression models were occasionally significant but explained little variance. Multiple regression models (using a forward stepwise approach) significantly increased the explained variance of these biodiversity models. Diversity models that emphasized species richness (rather than dominance or evenness) of the community, were preferred. These results suggest that much of the observed species richness/diversity is determined by abiotic pool conditions and represents an accumulation of tolerant species, either directly or indirectly (i.e. modulated by biotic interactions). However, regression models attempting to predict abundance/biomass based on abiotic variables explained less variance than did those predicting richness/diversity. This may indicate that biotic factors within pools at population or community levels are controlling species densities.