Are most species small? Not within species–level phylogenies

C. David, L. Orme, Nick J. B. Isaac, Andy Purvis

Abstract

The robust macro–ecological observation that there are more small–bodied species implies that smallbodied organisms have experienced elevated net rates of diversification. We investigate the role of body size in creating non–random differences in rates of cladogenesis using a set of 38 species–level phylogenies drawn from a range of animal groups. We use independent contrasts to explore the relationship between body size and species richness within individual phylogenies and across related sets of phylogenies. We also carry out a meta–analysis looking for associations between body size and species richness across the taxa. We find little evidence for increased cladogenesis among small–bodied organisms within taxa, and no evidence for any consistent differences between taxa. We explore possible explanations for the inconsistency of our findings with macro–ecological patterns.