INTRASEXUAL COMPETITION AND BODY-WEIGHT DIMORPHISM IN ANTHROPOID PRIMATES

Body weight dimorphism in anthropoid primates has been thought to be a consequence of sexual selection resulting from male-male competition for access to mates. However, while monogamous anthropoids show low de grees of weight dimorphism, as predicted by the sexual selection hypot hesis, polygynous anthropoids show high variation in weight dimorphism that is not associated with measures of mating system or sex ratio. T his observation has led many to debate the role of other factors such as dietary constraints, predation pressure, substrate constraints, all ometric effects, and phylogeny in the evolution of anthropoid weight d imorphism. Here, we re-evaluate variation in adult body weight dimorph ism in anthropoids, testing the sexual selection hypothesis using cate gorical estimates of the degree of male-male intrasexual competition ( ''competition levels''). We also test the hypotheses that interspecifi c variation in body weight dimorphism is associated with female body w eight and categorical estimates of diet, substrate use, and phylogeny. Weight dimorphism is strongly associated with competition levels, cor roborating the sexual selection hypothesis. Weight dimorphism is posit ively correlated with increasing female body weight, but evidence sugg ests that the correlation reflects an interaction between overall size and behavior, Arboreal species are, on average, less dimorphic than t errestrial species, while more frugivorous species tend to be more dim orphic than folivorous or insectivorous species. Several alternative h ypotheses can explain these latter results. Weight dimorphism is corre lated with taxonomy, but so too are competition levels. We suggest tha t most taxonomic correlations of weight dimorphism represent ''phyloge netic niche conservatism''; however, colobines show consistently low d egrees of weight dimorphism for reasons that are not clear. (C) 1997 W iley-Liss, Inc.