title: Ecology: is speciation driven by species diversity?
abstract: Emerson and Kolm show that the proportion of species endemic to an island is positively related to its species richness and, assuming that endemism indexes speciation rate, they infer that greater species diversity accelerates diversification. Here we demonstrate that the same correlation between species richness and percentage endemism can arise even if within-island speciation is negligible, particularly when both endemism and species richness depend on attributes of islands (such as area) that influence the average age of resident populations. Island biogeography theory indicates that, where the average time to extinction is relatively long, diversity increases through colonization, irrespective of whether new species are formed; at the same time, islands on which populations persist for longer accumulate more endemic species as local populations differentiate and populations on neighbouring islands become extinct. We therefore suggest that species richness and endemism are correlated fortuitously owing to their mutual dependence on the life spans of populations on islands, which is unrelated to speciation itself.
authors.affiliation: Department of Biology, University of Missouri, St Louis, Missouri 63121, USA. cdc35b@umsl.edu
authors.forename: Carlos Daniel
authors.initials: CD
authors.lastname: Cadena
authors.forename: Robert E
authors.initials: RE
authors.lastname: Ricklefs
authors.forename: Iván
authors.initials: I
authors.lastname: Jiménez
authors.forename: Eldredge
authors.initials: E
authors.lastname: Bermingham
mesh_terms: D000818:Animals; D044822:Biodiversity; D005075:Biological Evolution; D001717:Birds / Q000502:physiology; D005843:Geography; D008954:Models, Biological; D015203:Reproducibility of Results; D013045:Species Specificity; D014900:West Indies