Although there are numerous studies of the impact of herbivores on plants, most experimental studies are limited to small enclosures that do not fully account for the ways they may change community assembly via colonization-mediated processes. In a mesocosm study to overcomes some of these limitations, we found that herbivory accounted for about half of plant species richness and strongly altered the ability of plants to suppress nitrogen and phosphorus availability. Other factors such as eutrophication, stoichiometry and shading also affected plant composition (but not species richness) but did not have as big an impact. These results contrast with many previous experiments that did not adequately account for the ways colonization-extinction processes altered the role of herbivores and suggest that herbivory may be much more important that has been though.