Selection is more important than complementarity in global grasslands

A central question concerning biodiversity loss is how it impacts ecosystem functions and services. Experiments manipulating species diversity often show the complementarity effect, stemming from niche differentiation or facilitation among species, contributes dominantly to ecosystem functions. The selection effect, resulting from the increased likelihood of species-diverse communities containing high-performance species, plays a limited role. However, the applicability of these findings to natural ecosystems remains unclear. By partitioning the two effects and further separating them into dominant-species and subordinate-species components, we found that the selection effect was significant in enhancing natural grassland functions (plant biomass production and community coverage), and better predicted functions than the complementarity effect. In natural grasslands, the selection effect was largely driven by dominant species and independent from community-wide species diversity, while the complementarity effect was largely driven by subordinate species and positively associated with species diversity. Our results suggest that the selection effect may play a more important role in driving the functioning of natural ecosystems, which may be underestimated in biodiversity experiments.