Biodiversity is rapidly declining worldwide, and this may lead to subsequent declines in ecosystem functioning and stability. Here I consider whether: (i) stabilizing species interactions, such as niche partitioning and facilitation, promote biodiversity, ecosystem functioning, and stability, and (ii) global ecosystem changes influence biodiversity, ecosystem functioning, and stability by destabilizing species interactions.

In Chapters 2 and 3, I report results from studies that used long-term data from a grassland biodiversity experiment to identify the mechanisms that promoted biodiversity, productivity, and the temporal stability of productivity. Stabilizing species interactions that favored rare species promoted productivity and temporal stability. Stabilizing species interactions that favored unproductive species promoted biodiversity and temporal stability.

In Chapters 4 and 5, I report results from a new experiment that tested whether intense grazing influenced biodiversity, ecosystem functioning, and stability by favoring common and productive species, especially in exotic species mixtures. Stabilizing species interactions maintained biodiversity and promoted ecosystem functioning in ungrazed native species mixtures. However, species interactions were destabilized, and ecosystem functioning was decreased, in both exotic and intensely grazed mixtures.

In conclusion, these results suggest that: (i) stabilizing species interactions that favor rare and unproductive species can simultaneously promote biodiversity, ecosystem functioning, and temporal stability in grasslands; and (ii) changing from native grasslands to exotic grasslands or pastures can decrease ecosystem services by destabilizing species interactions.