Six conclusions have emerged from recent research that complicate the ability to predict how biodiversity losses may affect ecosystem function: (1) species traits determine ecosystem function, (2) species within functional groups are not always ecological equivalents, (3) biodiversity losses include declines in the abundance of common species, (4) biodiversity losses affect wholefood webs, (5) the effects of biodiversity losses depend on abiotic and biotic context and spatial and temporal scales, and (6) successfully predicting linkages between biodiversity and ecosystem function requires using multiple empirical approaches across scales. Nutrient recycling by freshwater mussel communities illustrates these conclusions. Nutrient excretion rates depend on the expression of mussel species traits, which vary with flow, temperature, and community structure. Nutrient contributions from mussels depend on which mussel species are dominant, but common species of mussels are declining, leading to shifts in species dominance patterns and thus nutrient recycling. These changes are very likely affecting the rest of the benthic food web because mussel excretion stimulates primary, and subsequently secondary, production.