title: Unifying latitudinal gradients in range size and richness across marine and terrestrial systems.
abstract: Many marine and terrestrial clades show similar latitudinal gradients in species richness, but opposite gradients in range size-on land, ranges are the smallest in the tropics, whereas in the sea, ranges are the largest in the tropics. Therefore, richness gradients in marine and terrestrial systems do not arise from a shared latitudinal arrangement of species range sizes. Comparing terrestrial birds and marine bivalves, we find that gradients in range size are concordant at the level of genera. Here, both groups show a nested pattern in which narrow-ranging genera are confined to the tropics and broad-ranging genera extend across much of the gradient. We find that (i) genus range size and its variation with latitude is closely associated with per-genus species richness and (ii) broad-ranging genera contain more species both within and outside of the tropics when compared with tropical- or temperate-only genera. Within-genus species diversification thus promotes genus expansion to novel latitudes. Despite underlying differences in the species range-size gradients, species-rich genera are more likely to produce a descendant that extends its range relative to the ancestor's range. These results unify species richness gradients with those of genera, implying that birds and bivalves share similar latitudinal dynamics in net species diversification.
authors.affiliation: Earth Science Institute, Slovak Academy of Sciences, 84005 Bratislava, Slovakia geoltoma@savba.sk.
authors.forename: Adam
authors.initials: A
authors.lastname: Tomašových
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, 2100 Copenhagen, Denmark.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Kennedy
authors.affiliation: Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Tristan J
authors.initials: TJ
authors.lastname: Betzner
authors.affiliation: Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Nicole Bitler
authors.initials: NB
authors.lastname: Kuehnle
authors.affiliation: Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Stewart
authors.initials: S
authors.lastname: Edie
authors.affiliation: Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Sora
authors.initials: S
authors.lastname: Kim
authors.affiliation: Committee on Evolutionary Biology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: K
authors.initials: K
authors.lastname: Supriya
authors.affiliation: Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Alexander E
authors.initials: AE
authors.lastname: White
authors.affiliation: Center for Macroecology, Evolution and Climate, Natural History Museum of Denmark, University of Copenhagen, 2100 Copenhagen, Denmark Department of Life Sciences, Imperial College London, Silwood Park Campus, Ascot, West Berkshire SL5 7PY, UK.
authors.forename: Carsten
authors.initials: C
authors.lastname: Rahbek
authors.affiliation: Senckenberg Biodiversity and Climate Research Center (BiK-F), 60325 Frankfurt am Main, Germany.
authors.forename: Shan
authors.initials: S
authors.lastname: Huang
authors.affiliation: Committee on Evolutionary Biology, University of Chicago, Chicago, IL 60637, USA Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Trevor D
authors.initials: TD
authors.lastname: Price
authors.affiliation: Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA Committee on Evolutionary Biology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: David
authors.initials: D
authors.lastname: Jablonski
mesh_terms: D000818:Animals; D001267:Atlantic Ocean; D044822:Biodiversity; D001717:Birds; D049872:Bivalvia; D017753:Ecosystem; D008954:Models, Biological; D010140:Pacific Ocean; D014329:Tropical Climate
keywords: Rapoport's rule; biogeography; latitudinal diversity gradient; range expansion; species–genus ratio