On tropical forests and their pests

Biologists have long been intrigued by the diversity of tropical forests, where 1 hectare may hold more than 650 tree species-more than in all of Canada and the continental United States. Eco- logical theory suggests that if species are too similar in their resource use, one will out- compete the others; hence, neighboring species must exploit different niches if they are to coexist. However, given that plants in one hectare of rainforest experience very similar physical environments, ecologists have struggled to demonstrate sufficient niche differentiation to support such high diversity (1). In addition to the puzzle of high local diversity, tropical forests also have high species richness overall. Recent studies show that interactions with pests may promote local plant diversity, accelerate plant evolution, and enhance the proliferation of species over evolutionary time.