Response diversity increases functional stability but decreases diversity and compositional stability of grassland communities

The insurance hypothesis of biodiversity assumes that ecosystem stability rises with increasing biodiversity because functionally redundant species respond differently to environmental changes, allowing some species to compensate for the loss of others. We tested this hypothesis by combining extensive field data and a common garden experiment where sods originating from different regions were subjected to land-use treatments. Based on plant species-specific performance-environment relationships with abundance as performance proxy and land-use intensity as environmental variable, we calculated response dissimilarity of species-pairs. The resulting dissimilarity matrix was used to calculate response diversity (functional dispersion) of grass sods before and after land-use treatments. Our results showed that high land-use intensity decreased response diversity of plant communities both in the field as well as in the common garden. Response diversity in grass sods increased functional stability but decreased stability in terms of species diversity and composition as communities with high response diversity lost species without replacement in response to experimental land-use change, while those with low response diversity showed species turnover. We conclude that response diversity is an important component of biodiversity and discuss future research directions to refine and generalize the concept of response diversity and its role in ecosystem stability.