Global signal of top-down control of terrestrial plant communities by herbivores

Significance A focus in ecology is understanding the processes that govern ecosystem productivity and biodiversity. A multitude of co-occurring biological mechanisms shape these properties in plant communities, but the relative importance of specific processes remains ambiguous, such as competition among individuals and species for resources (bottom-up regulation) and the role of herbivory in controlling plant populations (top-down regulation). In this global synthesis of herbivore impacts on terrestrial plants, we find strong evidence that herbivores regulate most plant communities, but their positive effects on diversity may be contingent on a subset of animals and specific habitats. We conclude that the strength of top-down regulation in terrestrial ecosystems appears more variable and context-dependent than in aquatic systems.