Theory suggests that an increase in biodiversity will stabilize aggregate community properties (e.g., the total productivity of a community) but destabilize individual components within the community (e.g., the productivity or abundances of individual species).  Although a growing amount of empirical work is beginning to support the first prediction, there is less empirical consensus on how biodiversity affects the stability of individual species. Furthermore, it is unclear whether the association between stability and biodiversity depends on the spatial scale of analysis. I compiled long term data (12 years) from herbaceous plant communities at the Jornada LTER site to examine how the biodiversity of a location affects 1) the stability of total community productivity, and 2) the stability of individual species productivity at both small (1 m²) and large (> 49 m²) spatial scales.

Results/Conclusions

I found that increasing biodiversity stabilizes total community productivity at both small and large spatial scales. In contrast, the association between biodiversity and stability of individual species varies with the spatial scale of analysis. At small spatial scales there was a non-significant trend for an increase in biodiversity to destabilize the productivities of individual species. Increasing biodiversity at large spatial scales increased the stability of individual species productivity but there was a saturating effect of biodiversity on stability. Preliminary analyses suggest that the portfolio effect (i.e., statistical averaging) is the dominant mechanism causing the patterns observed at the small spatial scale. The portfolio effect does not appear, however, to be causing the pattern of increased stability of both community and population productivities at large scales. Instead, increased stability in more diverse regions appears to be associated with a lower covariance (i.e., less synchrony) in the population dynamics of species in different plots comprising the region. The scale dependent patterns reported here suggest that spatial processes play an important role in maintaining the stability of ecological systems at large spatial scales.