Simple Rules for Interspecific Dominance in Systems with Exploitative and Apparent Competition

Herbivores and nutrients control grassland plant diversity via light limitation

“…2d and Extended Data Table 5, P , 0.001). This result is consistent with eutrophication-induced loss of niches for coexistence 8,9,19,28 and demonstrates the generality of eutrophication as a primary force controlling the diversity of grassland communities by reducing ground-level light 20 .…”

“…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.…”

“…Such widespread alteration of herbivores and nutrient supply may jointly determine the future diversity of ecosystems. For example, in highly productive, eutrophic systems in which plant species extinction is likely to occur owing to a loss of ecological niches 8 , ecological theory predicts that herbivores can act to maintain local-scale plant diversity if they selectively consume the superior resource competitors 9 . Empirical studies in many ecosystem types find highly variable effects of herbivores on plant species diversity [11][12][13] , with the magnitude of herbivore mediation of diversity frequently observed to be greatest in regions of high ecosystem productivity [11][12][13][14][15][16][17] .…”

“…These interactions result in a dynamic local community in which composition responds quickly to changes in the strength of nutrient limitation or herbivory 25,26 . In eutrophied systems, where nutrient limitation is alleviated and productivity is increased, theory predicts that these tradeoffs among plant strategies will simplify the plant community to species sharing an herbivore and competing for a single resourcelight 9,19 .…”

“…However, a critical assumption underlying the hypothesis that grassland diversity is jointly controlled by nutrient supply and consumers is that diversity should be rescued consistently by herbivory. In both ambient and eutrophied plots, herbivory should lead to greater diversity because herbivores can alleviate ground-level light limitation, thereby increasing the number of possible tradeoffs (nutrients, light) that maintain plant species diversity 9,16 . Table 1.…”