One basic summary of the spatial pattern of biodiversity across the surface of the Earth is
provided by a species–range size distribution, the frequency distribution of the numbers of
species exhibiting geographic ranges of different sizes. Although widely considered to be
approximately lognormal, increasingly it appears that across a variety of groups of
organisms this distribution systematically departs from such a form. Whatever its detailed
shape, however, the distribution must arise as a product of three processes, speciation …