Environmental Sciences Ph.D. Program

E.S. Ph.D. faculty member, John Stireman, recently coauthored a paper that deals with a central issue in ecology

photo of john stireman

(L. A. Dyer, M. S. Singer, J. T. Lill, J. O. Stireman, G. L. Gentry, R. J. Marquis, R. E. Ricklefs, H. F. Greeney, D. L. Wagner, H. C. Morais, I. R. Diniz, T. A. Kursar, P. D. Coley. 2007. Host specificity of Lepidoptera in tropical and temperate forests. Nature 448, 696–699 (09 Aug 2007)

How many animal species are there and how are they distributed?

Recent studies of insect herbivore diversity and host range in tropical systems have suggested that early estimates of 50 million animal species on earth (most of which are insects) are far too high because they make an incorrect assumption that most herbivores are highly specialized, particularly those in the tropics. In fact, some recent research suggests that insect herbivores are not as specialized as previously assumed and that Tropical insect herbivores are not more specialized than temperate ones.

In our paper we analyzed herbivore host range data and beta diversity among plant species from 8 extensive rearing studies of caterpillars spanning a latitudinal gradient from Canada to Brazil and found clear evidence that tropical caterpillars are more specialized than temperate caterpillars. This greater specialization is due (we think) to greater top-down and bottom-up selective forces in the tropics that favor specialization, and it suggests that the diversity of insect herbivores cannot be simply predicted from gradients in plant species diversity. It also suggests that recent estimates of earth's animal diversity are likely too low.