Observational evidence of a negative biodiversity-stability relationship in intertidal epibenthic communities

The idea that diversity begets the functioning and stability of ecosystems has been intensely examined in terrestrial habitats, yet these relationships remain poorly studied in the marine realm. Theoretical and empirical work suggest that diversity enhances the stability of communities, but decreases the stability of populations. This is because compensatory dynamics, such as when one species decreases while another increases, stabilise the community as long as species richness increases the variety of responses to the environment. In an observational field study, the temporal variability in species abundance was used as a measure of stability that was compared among 5 intertidal sites of naturally different species richness. Percent coverage of macrobenthic species was estimated every 6 mo for 2 yr. Stability in total community coverage was a negative but curvilinear function of species richness. In addition, the stability of single populations (averaged over all species) fluctuated across the species richness gradient, without showing the predicted negative pattern. We found no evidence for increasing compensatory dynamics with increasing species richness, suggesting that the variety of responses to environmental changes was unrelated to diversity. Diversity-stability relationships in natural communities may be more complex than those predicted by theory and manipulative experiments.