Aim: It is unclear how the stability of natural ecosystems and populations varies with biodiversity at spatial scales relevant to resource managers. This study evaluates whether theory and prior experiments adequately predict how stability varies with a measure of biodiversity, plant species richness, at multiple scales in naturally assembled ecosystems and assesses mechanisms through which biodiversity is proposed to affect stability.

Location: Chihuahuan desert. Historically, grasslands represented the dominant vegetation type in this landscape and shrubs were uncommon. Desertification has degraded many native grassland regions into one of several alternate states dominated by different shrub species and these regions differ in biodiversity.

Methods: Researchers at the Jornada long-term ecological research site have amassed 12 years of data on the primary productivity of individual plant species in 735 permanent 1-m2 plots distributed among 15 regions that were all historically grasslands. I used this information to describe the relationship between biodiversity and stability at the local (1 m2) and regional (3721 m2) scale and to evaluate mechanisms through which biodiversity is proposed to affect stability.

Results: At the local scale, ecosystem stability increased linearly with biodiversity while population stability tended to decline with biodiversity. At the regional scale, both ecosystem and population stability increased as a saturating function of biodiversity. Scale-dependent change in the biodiversity–stability relationship can be explained by the spatial insurance hypothesis, asynchrony in the local productivity dynamics of the average species, and a change in species evenness with scale that weakens statistical averaging.

Main conclusions: Results from small-scale experimental studies may not directly translate to larger spatial scales but they appear to predict patterns in natural communities at small spatial scales. These results suggest that the maintenance of high biodiversity over a large spatial area is essential for maintaining ecosystem services and reducing the potential for further species extinctions.