Can the tropical conservatism hypothesis explain temperate species richness patterns? An inverse latitudinal biodiversity gradient in the New World snake tribe Lampropeltini

Authors

  • R. Alexander Pyron,

    Corresponding author
    1. Department of Biology, The Graduate School and University Center, The City University of New York, 365 Fifth Avenue, New York, NY 10016, USA
    2. Department of Biology, The College of Staten Island, The City University of New York, 2800 Victory Blvd, Staten Island, NY 10314, USA
    Search for more papers by this author
  • Frank T. Burbrink

    1. Department of Biology, The College of Staten Island, The City University of New York, 2800 Victory Blvd, Staten Island, NY 10314, USA
    Search for more papers by this author

*Correspondence: R. Alexander Pyron, Department of Biology, The Graduate School and University Center, The City University of New York, 365 Fifth Avenue, New York, NY 10016, USA.
E-mail: rpyron@gc.cuny.edu

ABSTRACT

Aim  A latitudinal gradient in species richness, defined as a decrease in biodiversity away from the equator, is one of the oldest known patterns in ecology and evolutionary biology. However, there are also many known cases of increasing poleward diversity, forming inverse latitudinal biodiversity gradients. As only three processes (speciation, extinction and dispersal) can directly affect species richness in areas, similar factors may be responsible for both classical (high tropical diversity) and inverse (high temperate diversity) gradients. Thus, a modified explanation for differential species richness which accounts for both patterns would be preferable to one which only explains high tropical biodiversity.

Location  The New World.

Methods  We test several proposed ecological, temporal, evolutionary and spatial explanations for latitudinal diversity gradients in the New World snake tribe Lampropeltini, which exhibits its highest biodiversity in temperate regions.

Results  We find that an extratropical peak in species richness is not explained by latitudinal variation in diversification rate, the mid-domain effect, or Rapoport's rule. Rather, earlier colonization and longer duration in the temperate zones allowing more time for speciation to increase biodiversity, phylogenetic niche conservatism limiting tropical dispersal and the expansion of the temperate zones in the Tertiary better explain inverse diversity gradients in this group.

Main conclusions  Our conclusions are the inverse of the predictions made by the tropical conservatism hypothesis to explain higher biodiversity near the equator. Therefore, we suggest that the processes invoked are not intrinsic to the tropics but are dependent on historical biogeography to determine the distribution of species richness, which we refer to as the ‘biogeographical conservatism hypothesis’.

Ancillary