Stable coexistence and higher productivity are intrinsically linked in multispecies communities

Why species coexist and how diversity sustains ecosystem functioning are usually studied apart. A long-established concept captures both: the complementarity effect---the additional biomass produced by species in mixture. Here, we demonstrate that mixtures of species with negative complementarity are almost always either unfeasible or unstable, whereas a strong positive complementarity indicates a large potential for coexistence. Because a community's total yield settles long before the community composition does, this signal can be read as a predictor in communities still in flux: our analyses of four long-term biodiversity experiments show that transient negative complementarity precedes species loss. Thus, stable coexistence and higher productivity are intrinsically linked in multispecies communities. Biodiversity does not merely have beneficial effects on average; biodiversity that endures can only improve ecosystem functioning.