Non-random species losses diminish productivity under chronic nutrient enrichment

Background/Question/Methods

There is considerable theoretical and experimental evidence that random species losses can substantially decrease productivity in terrestrial, freshwater, and marine ecosystems. This has raised concerns that contemporary biodiversity declines might alter ecosystem functioning and decrease the provision of several ecosystem services. Some ecologists, however, have questioned the relevance of these results for conservation. Species losses are often non-random, which may or may not lead to changes in ecosystem functioning. Furthermore, global environmental changes might directly influence ecosystem processes much more than they indirectly influence ecosystem processes through their effects on biodiversity. For example, biodiversity effects might be negligible if nutrient enrichment increases productivity by reducing resource limitation much more than it decreases productivity by driving non-random biodiversity declines.

Results/Conclusions

Contrary to this expectation, here we found that nutrient enrichment drove non-random species losses that substantially diminished productivity over time. That is, although nutrient enrichment initially increased productivity, it also led to losses of plant species, including initially dominant species, which subsequently eroded productivity. Specifically, we found that productivity was decreased by ~ 40 g m^-2 yr^-1 for every non-random species loss caused by chronic nitrogen enrichment. Our results suggest that changes in biodiversity may mediate the long-term impacts of some global environmental changes on ecosystem functioning and services.