Engines of speciation: a comparative study in birds of prey.

Sexual selection as a promoter of speciation has received much attention in recent years, but has produced highly equivocal evidence. Here, I test whether sexual conflict is related to species richness among genera in accipitrid birds of prey using phylogenetically controlled comparative analyses. Increased species richness was associated with both 'male-win' as well as 'female-win' situations, i.e. males being able to promote gene flow through mating or females being able to restrict gene flow through female choice. Species richness was higher when plumage differed between males and females and in polygynous breeding systems compared with monogamous ones. To assess the relative importance of sexual conflict and natural selection as correlates of species richness simultaneously, I also performed a multivariate analysis of correlates of species richness. Population density, plumage polymorphism, geographic range size and breeding latitude were predictors of species richness for birds of prey. These results stress the importance of both sexual and natural selection in determining species richness but with a clear overall emphasis on natural selection in birds of prey.