The role of phylogeny and behavioral competition in the evolution of coexistence among primates

Abstract

No analysis of coexistence among primates has ever considered phylogenetic distances and behavioral competition. The present model proposes that high levels of behavioral competition strongly incite divergence of the respective positions of sympatric species in niches, especially when these species are closely related. This divergence is then reflected in the morphologies of coexisting species (individuals exploit new dimensions of niches and their associated morphologies are selected for) and consequently in their phylogenetic distances. Sister species (defined here as those from the same subgenus or same species group) are phylogenetically closer than kin species (of the same genus but different subgenera or species groups). Accordingly, if a minimum phylogenetic distance is a condition of stable coexistence, then kin (and higher ranking) species, but not sister species, are expected to coexist in ecological communities. Moreover, the intensity of behavioral competition among coexisting species should be inversely proportional to phylogenetic distance. (Taxa are said to have high levels of behavioral competition if they display high rates of aggressive behaviors and simultaneous low rates of grooming behaviors.) To test these hypotheses, 41 ecological communities were reviewed. The conclusions are that (i) primate sister species do coexist, but very exceptionally compared with kin species (Wilcoxon's signed ranks test, p < 0.0001), suggesting that coexistence is possible provided a minimum phylogenetic distance is respected; (ii) there is a negative relationship between taxonomic distance and the rate of aggression among sympatric primates (p = 0.04) and a positive relationship between this distance and the rate of interspecific grooming behaviors (p = 0.028), supporting the hypothesis that stable coexistence is possible if sympatric species reduce and maintain low levels of behavioral competition.