Biodiversity drives ecosystem multifunctionality: A meta-analysis

Background/Question/Methods

Two decades of experimental research have shown that biodiversity can significantly alter ecosystem functioning, and that this trend is robust across organisms, habitats, and scenarios of global change. Many of these experiments have measured multiple ecosystem processes, but analyses have considered these processes in isolation, despite the fact that society values ecosystems for their ability to provision multiple functions. Here, we conduct the first quantitative meta-analysis of the relationship between diversity and multiple ecosystem functions, or ecosystem multifunctionality, using data from 92 published manipulations of species richness. Specifically, we tested: (1) for turnover in the identity of the highest-performing species across functions; (2) whether increasing species richness increases the average level of multiple ecosystem functions; and (3) whether diversity pushes multiple functions above a given threshold of the maximum observed level of functioning.

Results/Conclusions

All three approaches revealed a positive effect of diversity on ecosystem multifunctionality. We found that, across all experiments, roughly two-thirds of all ecosystem responses measured were dominated by different species. There was also an increasing but saturating relationship between the number of species that performed best in monoculture and the number of functions. Linear mixed effects models showed that increasing species richness raised multifunctionality as measured by averaging across all ecosystem responses. Finally, diversity had a positive effect on the number of functions greater than a threshold when that threshold was at intermediate levels (30-75% of the maximum observed level of functioning). At higher thresholds, however, diversity had no detectable effect. Neither ecosystem type nor trophic level of the focal organisms affected the outcome of these results. In summary, existing evidence indicates that diversity generally enables multiple ecosystem functions to achieve moderate levels of function. It does not enable all functions to reach their highest levels. This may be due to trade-offs or other mechanisms that generate negative correlations among functions.