Herbivores and nutrients control grassland plant diversity via light limitation

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13144.html

Human alterations to nutrient cycles^{1, 2} and herbivore communities^{3, 4, 5, 6, 7} are affecting global biodiversity dramatically². 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^{8, 9}. 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.

There is saying in Chinese, “木秀于林风必摧之”， this is true for grass in the case of  herbivore present. In English, there is another proverb, “A squeaky wheel gets the oil.” This is the effect of nutrients.The herbivores and nutrients are two types of selection pressures.

In the society of human, the phenomenon is also true.