Environmental Warming and Biodiversity-Ecosystem Functioning in Freshwater Microcosms: Partitioning the Effects of Species Identity, Richness and Metabolism

Predicting the effects of global warming on biodiversity–ecosystem functioning (B–EF) relationships is complicated by potential interactions among abiotic and biotic variables at multiple levels of organisation, including adaptation within regional species populations and changes in community composition and species richness. We investigated the capacity for assemblages of three freshwater invertebrate consumer species (Asellus aquaticus, Nemoura cinerea and Sericostoma personatum) from temperate (southern England) and boreal (northern Sweden) regions to respond to expected shifts in temperature and basal resources, and quantified rates of a key ecosystem process (leaflitter decomposition). Predictions of assemblage metabolism, derived from allometric-body size and temperature scaling relationships, accounted for approximately 40%of the variance in decomposition rates. Assemblage species composition accounted for further variance, but species richness per se had no discernible effect. Regional differences were evident in rates of leaf decomposition across temperature and resourcemanipulations, and in terms of the processing efficiency of temperate and boreal consumers of the same species (i.e. after correcting for body size and metabolic capacity), suggesting that intraspecific variation among local populations could modulate B–EF effects. These differences have implications for extrapolating how environmental warming and other aspects of climate change (e.g. species range shifts) might affect important drivers of ecosystem functioning over large biogeographical scales