On the heritability of geographic range sizes

Within taxonomic groups, most species are restricted in their geographic range sizes, with only a few being widespread. The possibility that species-level selection on range sizes contributes to the characteristic form of such species-range size distributions has previously been raised. This would require that closely related species have similar range sizes, an indication of heritability of range sizes at the species level. Support for this view came from a positive correlation between the range sizes of closely related pairs of fossil mollusc species. We extend this analysis by considering the relationship between the geographic range sizes of 103 pairs of contemporary avian sister species. Range sizes in these sister species show no evidence of being more similar to each other than expected by chance. A reassessment of the mollusc data also suggests that the high correlation was probably overestimated because of the skewed nature of range size data. The fact that sister species tend to have similar life histories and ecologies suggests that any relationship between range sizes and biology is likely to be complicated and will be influenced by historical factors, such as mode of speciation and post-speciation range size transformations.