Regional plankton diversity as a buffer against environmental change in freshwater ecosystems

Many experiments show that species diversity at small, local scales affects ecosystems; however, conservation is concerned with extinctions of species across broad landscapes. The relevance of global or regional diversity to ecosystems therefore remains in question. I asked whether regional biodiversity in freshwater zooplankton affects the resilience and resistance of local ecosystems to the multiple stressors of warming and salinization. I hypothesised that dispersal of species from the regional community should buffer ecosystems against environmental change by providing species with traits adapted to the novel conditions. I subjected freshwater zooplankton communities in mesocosms that were either connected to or isolated from the larger regional species pool to a factorial manipulation of experimental warming and increased salinity. Dispersal introduced heat-tolerant regional taxa that were able to compensate for reductions in local taxa under warmed conditions. Dispersal also dampened the effects of warming on net primary productivity, suggesting that regional diversity can provide stability against some aspects of climate change. However, other measures of ecosystem performance like decomposition and sedimentation were affected by warming and salinity but not dispersal. The results indicate that regional biodiversity provides important insurance that can stabilize ecosystems in a dynamic environment. However, compensation by the regional biota could not buffer all ecosystem rates against all sources of stress. My results show that the connectivity of habitats to regional biodiversity introduces species with broad ranges of traits that can maintain some local ecosystem function in the face of environmental changes.Science, Faculty ofZoology, Department ofGraduat