Speciation and Extinction Drive the Appearance of Directional Range Size Evolution in Phylogenies and the Fossil Record
Alex L. Pigot 1,2,3*, Ian P. F. Owens 2,4, C. David L. Orme 2,3
1 Edward Grey Institute, Department of Zoology, University of Oxford, Oxford, United Kingdom, 2 Division of Biology, Department of Life Sciences, Imperial College
London, Ascot, United Kingdom, 3 Grantham Institute for Climate Change, Imperial College London, London, United Kingdom, 4 Natural History Museum, London, United Kingdom
Abstract
While the geographic range of a species is a fundamental unit of macroecology and a leading predictor of extinction risk, the evolutionary dynamics of species’ ranges remain poorly understood. Based on statistical associations between range size and species age, many studies have claimed support for general models of range evolution in which the area occupied by a species varies predictably over the course of its life. Such claims have been made using both paleontological data and molecular estimates of the age of extant species. However, using a stochastic model, we show that the appearance of trends in range size with species’ age can arise even when range sizes have evolved at random through time. This occurs because the samples of species used in existing studies are likely to be biased with respect to range size: for example, only those species that happened to have large or expanding ranges are likely to survive to the present, while extinct species will tend to be those whose ranges, by chance, declined through time. We compared the relationship between the age and range size of species arising under our stochastic model to those observed across 1,269 species of extant birds and mammals and 140 species of extinct Cenozoic marine mollusks. We find that the stochastic model is able to generate the full spectrum of empirical age–area relationships, implying that such trends cannot be simply interpreted as evidence for models of directional range size evolution. Our results therefore challenge the theory that species undergo predictable phases of geographic expansion and contraction through time.
Citation: Pigot AL, Owens IPF, Orme CDL (2012) Speciation and Extinction Drive the Appearance of Directional Range Size Evolution in Phylogenies and the Fossil
Record. PLoS Biol 10(2): e1001260. doi:10.1371/journal.pbio.1001260
Academic Editor: Craig Moritz, University of California Berkeley, United States of America
Received August 23, 2011; Accepted January 5, 2012; Published February 21, 2012
Copyright: 2012 Pigot et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was funded by a Grantham Studentship to ALP from the Grantham Institute for Climate Change, Imperial College London, and an RCUK Fellowship to CDLO. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: alex.pigot@zoo.ox.ac.uk
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