Ecologists need to know how particular processes influence biodiversity and ecosystem stability. We demonstrate how data from biodiversity-ecosystem functioning experiments can be used to identify and quantify the classes of mechanisms maintaining biodiversity and ecosystem stability. We predicted that three classes of mechanisms can maintain plant species diversity: 1) evenness stabilizing mechanisms, which favor rare species by allowing the least productive species to overyield most, 2) richness stabilizing mechanisms, which increase niche partitioning and positive species interactions, and 3) equalizing mechanisms, which minimize average fitness differences among species. Additionally, we predicted that evenness and richness stabilizing mechanisms would also promote ecosystem stability. We tested these predictions with annual peak biomass data from the first seven growing seasons of an ongoing study where grassland plant species evenness and richness were experimentally varied. We used path and multiple regression analyses to test the effects of these classes of mechanisms on changes in biodiversity and ecosystem stability.

Results/Conclusions  

We found that evenness stabilizing mechanisms maintained biodiversity by allowing the species that produced the least biomass in monoculture to benefit the most from species interactions in mixture. Richness and evenness stabilizing mechanisms promoted ecosystem stability. These results suggest that both maintenance of biodiversity and ecosystem stability can be promoted by processes that: 1) allow rare species to benefit the most from species interactions, and 2) maximize negative intraspecific interactions relative to negative interspecific interactions. This analysis can be applied to other existing data sets from biodiversity-ecosystem functioning experiments worldwide to determine the generality of our results. This framework will allow future experiments to identify and quantify the specific mechanisms that are driving the recent declines in biodiversity, and maintaining biodiversity and ecosystem stability.