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Abstract Detail


Paul, John R. [1], Morton, Cynthia [2], Tonsor, Stephen [3].

Explaining Variation in Geographic Range Size by Species Age: A Test Using Two Genera of Neotropical Plants.

Are many species with small geographic ranges simply young (recently diverged) species? If new species start with small population and range sizes, and if the probability of extinction is inversely related to population size, than there is an expectation of a positive species age and range size relationship. This relationship, originally proposed by Willis in 1992 as the Age-and-Area Hypothesis, is also a prediction of modern ecological theory (e.g., neutral theory). There have been few empirical tests of this pattern and the results have largely been equivocal. Furthermore, although the hypothesis was originally proposed based on observations of tropical plant species, all of the explicit tests have used animal species, many of which may be expected to undergo quick range-size transformations, and thus may be unlikely to exhibit a positive age and range size relationship for much of their evolutionary history. Using two genera of Neotropical understory shrubs, Psychotria (Rubiaceae) and Piper (Piperaceae), we test the age and area hypothesis. We use herbarium collection records to estimate range sizes and molecular divergence dates to estimate species ages. We show that species age can be a significant predictor of range size, explaining as much as a quarter of the variation in range sizes among species. We also show that consideration of the phylogenetic scale of the test and the ecological attributes of clades may strongly influence results. Finally, we discuss some of the methodological challenges posed by using molecularly-derived divergence times as species age estimates and potential solutions to these challenges.

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1 - University of Pittsburgh, Department of Biological Sceinces, 4249 Fifth Ave, 162 Crawford Hall, Pittsburgh, PA, 15260, USA
2 - Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania, 15213, USA
3 - University of Pittsburgh, Department of Biological Sciences, Langley Hall, Pittsburgh, Pennsylvania, 15260, USA

species age
geographic range size
divergence time

Presentation Type: Oral Paper:Papers for Topics
Session: CP01
Location: Boulevard B/Hilton
Date: Monday, July 9th, 2007
Time: 9:00 AM
Number: CP01005
Abstract ID:2181

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