Biodiversity at multiple trophic levels is needed for ecosystem multifunctionality

Both a high number of species and abundance in multiple trophic levels are required for ecosystems to continue to provide the services humans require of them. Numerous experiments have shown that the loss of biodiversity within single trophic groups — groups of organisms consuming resources from a similar level in the food chain — reduces the ability of ecosystems to deliver the services on which humans depend. How the loss of biodiversity in natural ecosystems consisting of multiple interacting trophic groups affects ecosystem functioning has remained unclear. Santiago Soliveres et al. have compiled data on the richness and abundance of 4,600 microbial, plant and animal taxa in 150 grasslands in Germany, together with information on 14 ecosystem services. Their analysis of the data demonstrates that biodiversity across multiple trophic groups is as important for the functioning of ecosystems as land-use intensity or environmental conditions. They conclude that the preservation of high levels of richness and diversity within a wide range of taxa will be key to ensuring that ecosystems continue to deliver the services on which humans rely. The findings also inform conservation and ecosystem management strategies by highlighting the most functionally relevant organisms, which include plants, soil bacteria and herbivorous insects. Many experiments have shown that loss of biodiversity reduces the capacity of ecosystems to provide the multiple services on which humans depend1,2. However, experiments necessarily simplify the complexity of natural ecosystems and will normally control for other important drivers of ecosystem functioning, such as the environment or land use. In addition, existing studies typically focus on the diversity of single trophic groups, neglecting the fact that biodiversity loss occurs across many taxa3,4 and that the functional effects of any trophic group may depend on the abundance and diversity of others5,6. Here we report analysis of the relationships between the species richness and abundance of nine trophic groups, including 4,600 above- and below-ground taxa, and 14 ecosystem services and functions and with their simultaneous provision (or multifunctionality) in 150 grasslands. We show that high species richness in multiple trophic groups (multitrophic richness) had stronger positive effects on ecosystem services than richness in any individual trophic group; this includes plant species richness, the most widely used measure of biodiversity. On average, three trophic groups influenced each ecosystem service, with each trophic group influencing at least one service. Multitrophic richness was particularly beneficial for ‘regulating’ and ‘cultural’ services, and for multifunctionality, whereas a change in the total abundance of species or biomass in multiple trophic groups (the multitrophic abundance) positively affected supporting services. Multitrophic richness and abundance drove ecosystem functioning as strongly as abiotic conditions and land-use intensity, extending previous experimental results7,8 to real-world ecosystems. Primary producers, herbivorous insects and microbial decomposers seem to be particularly important drivers of ecosystem functioning, as shown by the strong and frequent positive associations of their richness or abundance with multiple ecosystem services. Our results show that multitrophic richness and abundance support ecosystem functioning, and demonstrate that a focus on single groups has led to researchers to greatly underestimate the functional importance of biodiversity.