Evidence for ecological character displacement must include correlation between the morphological character in question and the function of that character in the organisms' environment. Examination of the cranial skeletons and jaw components of sympatric populations of Plethodon cinereus and Plethodon hoffmani correlate well with the sympatric shift in diet in these two species relative to their respective allopatric populations. This hypothesized relationship between cranial features and diet is consistent with ecological character displacement. A biomechanical model predicts a stronger, slower jaw in sympatric P. cinereus and a faster, weaker jaw in P. hoffmani relative to their respective allopatric populations. Inherent in this model is the assumption that no differences in the jaw muscles exist. Here we test this assumption using data on jaw muscle mass and tooth number in sympatric and allopatric populations of P. cinereus and P. hoffmani. Our findings indicate significant differences between species, but no consistent pattern of character displacement in these structures. We discuss the consistency of our data with the previously proposed biomechanical model and alternative hypotheses.
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