Abundance and species richness in natural aquatic microcosms: a test and refinement of the Niche-Limitation Hypothesis

The Energy-Limitation Hypothesis (ELH) predicts that species richness is an increasing function of abundance. In contrast, the Niche-Limitation Hypothesis (NLH) predicts that high abundances become easier to attain as species richness increases. We tested the NLH and ELH using aquatic invertebrate communities of tropical rock pools. These rock pools span a gradient from very low density pools N < 200 individuals/liter) to very high density pools (N > 5001). Only in low density rock pools were species richness and abundance positively related. In intermediate abundance rock pools no relationship between species richness and abundance was observed, and in high abundance rock pools the relationship between species richness and abundance was strongly negative. These patterns are inconsistent with the predictions of the ELH, but not with predictions of the modified NLH which adds carrying capacity to the model.