Disturbance and Aquatic Biodiversity: Reconciling Contrasting Views

Opinions about how disturbance affects stream biodiversity differ. Models that assume that communities are shaped by biotic interactions emphasize the positive effects of stream disturbance (such as possible colonization by species that would be outcompeted under stable environmental conditions), whereas models assuming that communities are shaped by physical habitat factors emphasize the negative effects (such as the exclusion of species lacking adaptations to stress). Empirical studies on macroinvertebrate assemblages show that at small spatial scales, disturbance caused by floods affects diversity negatively. However, the same mechanisms that disturb the biota—scour and fill of sediments—also maintain the heterogeneity of riverine habitats, which underpins the existence of rich communities in the long term and at larger spatial scales. Therefore, the effects of flood-mediated disturbance on biodiversity probably depend on the spatiotemporal scale of observation. The magnitude of the observed effects is modulated by the predictability and severity of floods and the availability of food resources.