The paradox of the phylogeny: Character displacement of analyses of body size in island Anolis

Abstract

The evolution of body size in Anolis lizards of the Lesser Antilles Islands has been the subject of intensive, if divisive, study. Early research by Schoener revealed a regularity in the number of Anolis species that coexisted on islands and the difference in body size between coexisting congeners in the Northern Lesser Antilles. This consistent pattern of body size was suggested to be the result of competitive character displacement. Two recent studies critically evaluated this hypothesis by incorporating information about the phylogenetic relationships of insular Anolis. Roughgarden and Pacala suggested that the patterns of body-size differences in the Northern Lesser Antilles could be explained as a cyclical phenomenon that they labeled a taxon cycle. However, Losos supported the character-dis-placement hypothesis ("size adjustment"). The conflict between these two studies is important because both investigations were based on the same phylogenetic hypothesis. We investigated body-size evolution in Lesser Antilles Anolis to resolve the differences in the conclusions of these studies. Our new analysis supported the taxon-cycle hypothesis but nevertheless failed to reject the character-displacement hypothesis. We argue that this curious scenario is largely a function of the method by which phylogenetic information is incorporated in comparative analyses. Different comparative analyses may lead to dramatic differences in results and ambiguity in the conclusions to be drawn. We suggest that ecologists and evolutionary biologists specifically consider the underlying assumptions and models of character evolution inherent to each of the phylogenetically based analytical methods now available.