Interacting effects of herbivory and fertility on a synthesized plant community

1 Outdoor microcosms were used to investigate the effects of invertebrate herbivory on plant community composition, and thereby infer possible effects on the rate of secondary succession, at differing levels of soil fertility, 2 A mixture containing 24 grassland plant species of widely different functional types was established, with 12 microcosms at each of three fertility levels. Four generalist herbivores (Helix aspersa, Cepaea hortensis, Arianta abustorum and Sitobion avenae) were added to half of the microcosms. Above-ground biomass of each species was harvested after 2 years. Reproductive variables were also measured for one species, Poa annua. 3 At both moderate and high soil fertility generalist invertebrate herbivores fed selectively on early successional, fast-growing species, thus increasing the relative abundance of later successional, slow-growing species. This supports the hypothesis that herbivory increases the rate of secondary succession. Flowering and viable seed production of early successional ephemerals was also reduced by the invertebrate herbivores across a wide range of soil fertility. This would seriously reduce the ability of a species to persist in the community, thereby further hastening the rate of succession.