| Summary: | 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.
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