EXPERIMENTAL TESTS OF THE DEPENDENCE OF ARTHROPOD DIVERSITY ON PLANT DIVERSITY

Because a diversity of resources should support a diversity of consume rs, most models predict that increasing plant diversity increases anim al diversity. We report results of a direct experimental test of the d ependence of animal diversity on plant diversity. We sampled arthropod s in a well-replicated grassland experiment in which plant species ric hness and plant functional richness were directly manipulated. In simp le regressions, both the number of species planted (log(2) transformed ) and the number of functional groups planted significantly increased arthropod species richness but not arthropod abundance. However, the n umber of species planted was the only significant predictor of arthrop od species richness when both predictor variables were included in ANO VAs or a MANOVA. Although highly significant, arthropod species richne ss regressions had low R-2 values, high intercepts (24 arthropod speci es in monocultures), and shallow slopes. Analyses of relations among p lants and arthropod trophic groups indicated that herbivore diversity was influenced by plant, parasite, and predator diversity. Furthermore , herbivore diversity was more strongly correlated with parasite and p redator diversity than with plant diversity. Together with regression results, this suggests that, although increasing plant diversity signi ficantly increased arthropod diversity, local herbivore diversity is a lso maintained by, and in turn maintains, a diversity of parasites and predators.