Low beta diversity of herbivorous insects in tropical forests

Insects everywhere Insects are a major force in most ecosystems, yet in studies of biodiversity they often receive less attention than birds, mammals and plants. Two papers this week redress the balance. Novotny et al. studied some 500 species of lepidopteran caterpillars, beetles and fruit flies across 75,000 km2 of rain forest in Papua New Guinea. They found that most species of herbivorous insects were widely distributed. Species richness was high, as expected in the tropics, but the species found did not alter much even over hundreds of kilometres. Dyer et al. reached rather different conclusions from their work on hundreds of thousands of host-specificity feeding records for butterfly and moth caterpillars from areas ranging from Canada to Brazil. They found that the average number of tree species on which an insect species feeds was fewer in the tropics than in temperate parts of the New World, a confirmation of the latitudinal gradient in ecological specialization much discussed by biologists since the time of Darwin and Wallace. With apparently contradictory results such as these two reports, though, the discussion may run and run.