Dyer et al. 2007

Dyer LA, Singer MS, Lill JT, Stireman JO, Gentry GL, Marquis RJ, Ricklefs RE, Greeney HF, Wagner DL, Morais HC, Diniz IR, Kursar TA, Coley PD. 2007. Host specificity of Lepidoptera in tropical and temperate forests. Nature 448: 696-700.

These authors examined thousands of species of caterpillars and host plants in the New World from southern Canada to Brazil. They were testing the hypothesis that greater niche specialization accounts for higher species richness in tropical regions. They measured ecological specialization along a latitudinal gradient by quantifying diet breadth in caterpillars and beta diversity of caterpillars on widespread focal tree species. Host plant specificity of forest caterpillars decreased with increasing latitude. They were able to control for varying sampling area and sampling effort, but not for phylogeny.

Possible explanations for this trend include the probability that tropical plants are chemically “nastier”, prompting stronger selection among herbivores for specialization in diet, under the assumption (not stated in this paper) that tradeoffs exist among strategies for dealing with plant chemical defences. The trend of increased tropical specialization could be strengthened if, as is likely, widespread and generalized tropical species are actually assemblies of cryptic specialists (i.e. conserved morphology but reproductive isolation and local specialization for diet). Additionally, temperate species of both Lepidoptera and trees are generally better-studied than their tropical counterparts, suggesting that many more species of highly specialized and possibly cryptic herbivores await description in the tropics.

This paper appears in an issue of Nature with a paper by Novotny et al. (2007). Both papers are summarized in a “News & Views” by Stork (2007), as they found apparently contradictory results.