Annual variation of community biomass is lower in more diverse stream fish communities

Anthropogenic infl uences have disproportionally aff ected freshwater ecosystems, and a loss of biodiversity is forecasted to greatly reduce ecosystem function and services. Loss of species may destabilize communities by limiting the stabilizing forces of compensatory dynamics and/or statistical averaging, both of which are eff ects that can buff er variation in aggregate community properties. Currently, support for positive diversity-stability relationships stems from experiments with simple communities at small spatial and temporal scales, and application to natural communities is limited. Using a long-term dataset of 35 stream fi sh communities matched with hydrologic data, we show that community stability (annual variation of standing biomass of fi shes) was less variable in more species-rich communities and was not associated with stream hydrology. Only the statistical averaging model of community stability was consistent with observed patterns of lower biomass variation in more species-rich communities. Our fi ndings suggest anthropogenically induced extirpation of vertebrate consumers may lower community biomass stability in complex ecosystems.