Climatic zonation drives latitudinal variation in speciation mechanisms

Kenneth H. Kozak, John J. Wiens

Research output: Contribution to journalArticlepeer-review

161 Scopus citations


Many groups of organisms show greater species richness in the tropics than in the temperate zone, particularly in tropical montane regions. Forty years ago, Janzen suggested that more limited temperature seasonality in the tropics leads to greater climatic zonation and more climatic barriers to organismal dispersal along elevational gradients in the tropics relative to temperate regions. These factors could lead to differences in how species arise in tropical versus temperate regions and possibly contribute to greater tropical diversity. However, no studies have compared the relationships among climate, elevational distribution and speciation in a group inhabiting both tropical and temperate regions. Here, we compare elevational and climatic divergence among 30 sister-species pairs (14 tropical, 16 temperate) within a single family of salamanders (Plethodontidae) that reaches its greatest species richness in montane Mesoamerica. In support of Janzen's hypothesis, we find that sister species are more elevationally and climatically divergent in the tropics than in the temperate zone. This pattern seemingly reflects regional variation in the role of climate in speciation, with niche conservatism predominating in the temperate zone and niche divergence in the tropics. Our study demonstrates how latitudinal differences in elevational climatic zonation may increase opportunities for geographical isolation, speciation and the associated build-up of species diversity in the tropics relative to the temperate zone.

Original languageEnglish (US)
Pages (from-to)2995-3003
Number of pages9
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1628
StatePublished - Dec 7 2007


  • Climate
  • Elevation
  • Latitude
  • Niche evolution
  • Speciation
  • Species richness


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