TROPHIC INTERACTIONS AND PLANT-SPECIES RICHNESS ALONG A PRODUCTIVITY GRADIENT

We analyzed the interactive effects of trophic structure and disturban ce on species diversity of plant communities along a productivity grad ient by merging the intermediate disturbance hypothesis with a simple three-trophic-level predator-prey model. In two-trophic-level systems, i.e. without carnivores, the model produces a unimodal, hump-shaped p attern of species richness, which is consistent with patterns predicte d from other models. If carnivores are included, trophic cascades prod uce a bimodal pattern of species richness over the productivity gradie nt. We have found no appropriate data sets in the literature with whic h to assess the validity of our model. We thus offer the model as an a lternative hypothesis to be tested regarding plant species richness in productivity gradients, and as a reminder of the importance of trophi c structure for patterns and processes in plant communities.