A new study published today (June 14) in Ecology Letters provides experimental evidence for a an assumption of evolutionary biology accepted since Darwin first proposed it in 1859′s On the Origin of Species—that competition is greater among closely related species.”

That is the opening quote from a recent news article in The Scientist. The full article may be found here. The original research paper is in the most recent issue of Ecology Letters. The article doesn’t quite get this right, does it? It has NOT been a long-standing assumption of Darwinian theory that phylogenetic relatedness on its own drives competition. Phylogenetic relatedness is correlated with the frequency and intensity of competition to the extent that it reflects phenotypic overlap or similarity, which in turn will be a major factor in the extent of overlap in resource utilization. Extinction risk, therefore, is not a direct function of phylogenetic relatedness, at least not from the standpoint of competition for prey and other resources. It could play a role in terms of, say, resistance to predation or disease. To emphasize, two distantly related species will face the same risk if their phenotypic resource utilization is comparable to that of two significantly more closely related species. The journal article tests the effects of both trait and phylogenetic similarity, and conclude that phylogenetic similarity is a better predictor of the outcome of coexistence. I don’t understand how this could be the case, unless unmeasured traits are underlying factors. Am I missing something here?