If species' ranges are randomly shuffled within a bounded geographical domain free of
environmental gradients, ranges overlap increasingly toward the center of the domain,
creating a “mid-domain” peak of species richness. This “mid-domain effect”(MDE) has been
controversial both in concept and in application. Empirical studies assess the degree to
which the evolutionary, ecological, and historical processes that undeniably act on
individual species and clades produce geographical patterns that resemble those produced …