Fig. 1

The diversity of the herbivore community (expressed as richness of functional groups of herbivores) can have different effects on tundra ecosystem dynamics (i.e., processes, functions, or properties of tundra ecosystems). These effects can be: a additive, where increasing diversity of herbivores leads to strong directional changes in the outcome variable; b compensatory, where the effects of different functional groups of herbivores can compensate each other; or c no effect, where the outcome variable is not affected by differences in herbivore diversity. We expect the effects of multiple herbivores on ecosystem dynamics to be greater than the effects of single groups of herbivores, although the slope and direction of this relationship can change depending on the response being considered