Species-level heritability reaffirmed: a comment on "on the heritability of geographic range sizes"

For many current issues in macroevolution and macroecology, it is important to know to what degree the attributes of species are shared among closely related lineages, a concept sometimes referred to as species-level heritability. Recently, Webb and Gaston proposed a new method for analyzing the heritability of geographic range size and concluded that range size is not heritable in Cretaceous gastropods (data from Jablonski) and modern birds (their data). Here we show that Webb and Gaston's method is flawed in that it implicitly assumes that range sizes are uniformly distributed. When range size distributions show their characteristic strong right skew, Webb and Gaston's method spuriously tends to find that range sizes of closely related pairs of species are more dissimilar than the random expectation. A reanalysis of Jablonski's data finds range size to be robustly and strongly heritable in Cretaceous gastropods and less strongly but still significantly heritable in present-day birds.