ABSTRACT
Plant species diversity is greatest in tropical forest. Microbes, fungi, and animals consume living plant tissue. These pests may contribute to the coexistence of their host plant species if the more abundant plant species or the superior competitors suffer disproportionately high levels of damage. The relationship between pest pressure and the local population density of host plants becomes critical at larger spatial scales. Plant diversity is, in turn, enhanced in wet forests if the more abundant plant species or the superior competitors suffer disproportionately high levels of damage. Life history trade-offs occur among tropical forest plants. The number of seeds produced and the mass of individual seeds are inversely related. Trees and lianas suppress understory plants, and, as a result, direct interactions among understory plants are unlikely. To summarize, pests maintain low stem densities that prevent competition among understory plants, and chance sunflecks and treefall gaps largely determine which individuals succeed.
