Data from: revisiting niche divergence hypothesis in dimorphic birds: is diet overlap correlated with sexual size dimorphism?

The evolution of sexual size dimorphism (SSD) is a long-standing topic in
evolutionary biology, but there is little agreement on the extent to which
SSD is driven by the different selective forces. While sexual selection
and fecundity selection have traditionally been proposed as the two
leading hypotheses, SSD may also result from natural selection through
mechanisms such as sexual niche divergence, which might have reduced
resource competition between sexes. Here, we revisited the niche
divergence hypothesis by testing the relationship between the sexual
overlap in diet and SSD of 56 bird species using phylogenetic comparative
analyses. We then assessed how SSD variation relates to the three main
hypotheses: sexual selection, fecundity selection, and sexual niche
divergence using phylogenetic generalized least squares (PGLS). Then, we
compared sexual selection, fecundity selection, and niche divergence
selection as SSD drivers through phylogenetic confirmatory path analyses
to disentangle the possible causal evolutionary relationships between SSD
and the three hypotheses. Phylogenetic generalized least squares showed
that SSD was negatively correlated with diet overlap, i. e., the greater
the difference in body size between males and females, the less diet
overlap. As predicted by sexual selection theory, the difference in body
size between sexes was higher in polygynous species. Confirmatory
phylogenetic path analyses suggested that the most likely evolutionary
path might include mating system as a main driver in SSD and niche
divergence as a result of SSD. We found no evidence of a role of fecundity
selection in the evolution of female-biased SSD. Our study provides
evidence that sexual selection has likely been the main cause of SSD and
that dietary divergence is likely an indirect effect of SSD.