Two decades of research have not established whether tropical insect herbivores are dominated by specialists or generalists. This impedes our understanding of species coexistence in diverse rainforest communities. Host specificity and species richness of tropical insects are also key parameters in mapping global patterns of biodiversity. Here we analyse data for over 900 herbivorous species feeding on 51 plant species in New Guinea and show that most herbivorous species feed on several closely related plant species. Because species-rich genera are dominant in tropical floras, monophagous herbivores are probably rare in tropical forests. Furthermore, even between phylogenetically distant hosts, herbivore communities typically shared a third of their species. These results do not support the classical view that the coexistence of herbivorous species in the tropics is a consequence of finely divided plant resources; non-equilibrium models of tropical diversity should instead be considered. Low host specificity of tropical herbivores reduces global estimates of arthropod diversity from 31 million (ref. 1) to 4-6 million species. This finding agrees with estimates based on taxonomic collections, reconciling an order of magnitude discrepancy between extrapolations of global diversity based on ecological samples of tropical communities with those based on sampling regional faunas.
Bibliographical noteFunding Information:
We thank S. Naeem, J. T. Wootton, J. Bergelson, C. Pfister and M. Huston for comments on the manuscript, and J. Chase and J. Shurin for help in the field. The paper is a Kellogg Biological Station contribution, and was supported by grants from the National Science Foundation, US Department of Education, and the University of Chicago.
We thank parataxonomists J. Auga, W. Boen, C. Dal, S. Hiuk, B. Isua, M. Kasbal, R. Kutil, M. Manumbor and K. Molem and also K. Darrow and N. Heidari for assistance; many insect collectors and taxonomists are acknowledged elsewhere. N. Stork, T. Lewinsohn, J. Zrzavy, J. Leps and A. Stewart commented on the manuscript. This work was supported by the National Science Foundation (USA), Christensen Fund (USA), Grant Agency of the Czech Republic, Czech Academy of Sciences, the Swedish Natural Science Research Council, Czech Ministry of Education, Otto Kinne Foundation, Darwin Initiative (UK), International Centre of Insect Physiology and Ecology (ICIPE) and Bishop Museum.