Sexual Dimorphism and Species Diversity: from Clades to Sites

A variety of relationships have been observed between sexual dimorphism and species diversity, from positive to negative and nonsignificant. Although many hypotheses have been proposed to explain these relationships, it has proven difficult to understand why patterns are so variable. Most studies on this topic have used clades as phylogenetically independent replicates for pattern analysis, but a few recent studies took an alternative approach, using sites as spatially independent replicates. We discuss how the new, site-based studies complement the traditional, clade-based studies and argue that the combined use of the two approaches will be more powerful than either alone in understanding environmental factors that produce variation in sexual dimorphism-species diversity relationships.