title: The mid-domain effect revisited.
abstract: We revisit the proposition that boundary constraints on species' ranges cause species richness gradients (the mid-domain effect [MDE] hypothesis). In the absence of environmental gradients, species should not retain their observed range sizes as assumed by MDE models. Debate remains regarding the definition of domain limits, valid predictions for testing the models, and their statistical assessment. Empirical support for the MDE is varied but often weak, suggesting that geometric constraints on species' ranges do not provide a general explanation for richness gradients. Criticism of MDE model assumptions does not, however, imply opposition to the use of null models in ecology.
authors.affiliation: Department of Biology, Universidad de Valle, Apartado Aéreo 25360, Cali, Colombia. fazapata@univalle.edu.co
authors.forename: Fernando A
authors.initials: FA
authors.lastname: Zapata
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Gaston
authors.forename: Steven L
authors.initials: SL
authors.lastname: Chown
mesh_terms: D004463:Ecology; D017753:Ecosystem; D008954:Models, Biological; D012680:Sensitivity and Specificity; D013045:Species Specificity