Patterns in the geographic ranges of the world's woodpeckers

We used data on the world's woodpeckers to test for patterns in the geographic distributions of a single group of closely related species. The frequency distribution of woodpecker geographic range sizes is approximately lognormal, Most variation in range sizes is explained by differences between species within genera; that is, range size seems to be an evolutionarily labile trait. The largest woodpecker ranges are found in Eurasia, both when absolute differences are compared and when range size is measured as a proportion of estimated available habitat, Notably, there is a negative relationship between the mean range sizes attained by species in a genus or tribe in South America and the mean ranges attained by species in the same tribe or genus in North America, Large-bodied species tend to be more widely distributed and to live at higher latitudes, but both tendencies disappear if the taxonomic relatedness of species is controlled for. Species living at high latitudes also tend to be more widely distributed. This relationship seems largely due to the effect of North American woodpeckers, which, show it even when the taxonomic relatedness of species is controlled. Small continents generally have more woodpecker species than do large ones. Woodpecker geographic range sizes are smaller the more woodpecker species inhabit: an area. Species show less overlap in their geographic ranges with species of similar than with species of dissimilar body size. The implications of these results for our understanding of patterns in geographic range sizes are discussed.