A Tale of Two Salamanders

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Science  05 May 2000:
Vol. 288, Issue 5467, pp. 773
DOI: 10.1126/science.288.5467.773g

Evolutionary ecologists have theorized that two closely related animal species may be almost indistinguishable when they occupy different geographical areas, but show increased morphological or behavioral divergence in areas where their distributions overlap (sympatry). This phenomenon, called character displacement, is explained as a result of increased competitive pressure between sympatric species: competition tends to drive them to exploit different kinds of prey. Despite its theoretical appeal, however, character displacement has been demonstrated unequivocally in relatively few instances.

In a study of sympatric North American salamanders of the genus Plethodon, Adams and Rohlf apply new morphometric techniques to show how the jaw morphology and mechanics (the ratio of squamosal length to dentary length is proportional to closing force and inversely proportional to closing speed) of two salamander species have diverged in sympatry to allow capture of arthropod prey of different size and agility. Their results provide a solid example of character displacement and strengthen the case for the role it plays in the coexistence of species.—AMS

Proc. Natl. Acad. Sci. U.S.A.97, 4106 (2000).

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