Herbivores and nutrients control grassland plant diversity via light limitation.
Borer ET., Seabloom EW., Gruner DS., Harpole WS., Hillebrand H., Lind EM., Adler PB., Alberti J., Anderson TM., Bakker JD., Biederman L., Blumenthal D., Brown CS., Brudvig LA., Buckley YM., Cadotte M., Chu C., Cleland EE., Crawley MJ., Daleo P., Damschen EI., Davies KF., DeCrappeo NM., Du G., Firn J., Hautier Y., Heckman RW., Hector A., HilleRisLambers J., Iribarne O., Klein JA., Knops JMH., La Pierre KJ., Leakey ADB., Li W., MacDougall AS., McCulley RL., Melbourne BA., Mitchell CE., Moore JL., Mortensen B., O'Halloran LR., Orrock JL., Pascual J., Prober SM., Pyke DA., Risch AC., Schuetz M., Smith MD., Stevens CJ., Sullivan LL., Williams RJ., Wragg PD., Wright JP., Yang LH.
Human alterations to nutrient cycles and herbivore communities are affecting global biodiversity dramatically. Ecological theory predicts these changes should be strongly counteractive: nutrient addition drives plant species loss through intensified competition for light, whereas herbivores prevent competitive exclusion by increasing ground-level light, particularly in productive systems. Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory. This experiment, replicated in 40 grasslands on 6 continents, demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate. Nutrient addition consistently reduced local diversity through light limitation, and herbivory rescued diversity at sites where it alleviated light limitation. Thus, species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light.