The relative contribution of species richness and species composition to ecosystem functioning

The influence of species diversity on ecosystem functioning has been the subject of many experiments and remains a key question for ecology and conservation biology. However, the fact that diversity cannot be manipulated without affecting species composition makes this quest methodologically challenging. We used partial Mantel tests to evaluate the relative importance of diversity and of composition on biomass production. Here, we applied partial Mantel tests (controlling for the other variable) on two datasets, the Jena (2002–2008) and the Grandcour (2008–2009) Experiment. In both experiments, plots were sown with different numbers of species to unravel mechanisms underlying the biodiversity-ecosystem functioning relationships. Contrary to Jena, plots were not mowed nor weeded in Grandcour, allowing external species to establish. Based on the diversity–ecosystem functioning and competition theories, we tested two predictions: 1) the contribution of composition should increase with time...