Methods and data sources
The following journals were searched: Science journals:Science, Nature, Proceedings of the National Academy of Sciences USA; Ecology journals:Ecology, Ecological Monographs, Ecological Applications, Oecologia, Oikos, Ecology Letters, Journal of Ecology, Journal of Animal Ecology; Marine journals: Limnology and Oceanography,Marine Biology, Marine Ecology Progress Series, Journal of Experimental Marine Biology andEcology, Journal of the Marine Biological Association of the United Kingdom.
We grouped studies according to trophic level (primary producer or consumer) and response variable (resource use, primary or secondary production, nutrient cycling, and resilience). For each variable, we conducted a meta-analysis comparing the log ratio of responses in the highest diversity treatment over the average of all single-species treatments. The effect size was weighted by the sample sizes and standard deviations derived from the original study. Response ratios were combined by fixed-effects meta-analysis. Weights for the log-response ratios were estimated based on sample variance and sample size from the individual studies.