Functional identity and diversity of animals predict ecosystem

40 Drastic biodiversity declines have raised concerns about the deterioration of ecosystem 41 functions and have motivated much recent research on the relationship between species diversity 42 and ecosystem functioning. A functional trait framework has been proposed to improve the 43 mechanistic understanding of this relationship, but this has rarely been tested for organisms other 44 than plants. We analyzed eight data-sets, including five animal groups, to examine how well a trait45 based approach, compared with a more traditional taxonomic approach, predicts seven ecosystem 46 functions below and above ground. Trait-based indices consistently provided greater explanatory 47 power than species richness or abundance. The frequency distributions of single or multiple traits in 48 the community were the best predictors of ecosystem functioning. This implies that the ecosystem 49 functions we investigated were underpinned by the combination of trait identities (i.e., single-trait 50 indices) and trait complementarity (i.e., multi-trait indices) in the communities. Our study provides 51 new insights into the general mechanisms that link biodiversity to ecosystem functioning in natural 52 animal communities and suggests that the observed responses were due to the identity and 53 dominance patterns of the trait composition rather than the number or abundance of species per se. 54