Geometric constraints explain much of the species richness pattern in African birds

May 8, 2001
98 (10) 5661-5666

Abstract

The world contains boundaries (e.g., continental edge for terrestrial taxa) that impose geometric constraints on the distribution of species ranges. Thus, contrary to traditional thinking, the expected species richness pattern in absence of ecological or physiographical factors is unlikely to be uniform. Species richness has been shown to peak in the middle of a bounded one-dimensional domain, even in the absence of ecological or physiographical factors. Because species ranges are not linear, an extension of the approach to two dimensions is necessary. Here we present a two-dimensional null model accounting for effects of geometric constraints. We use the model to examine the effects of continental edge on the distribution of terrestrial animals in Africa and compare the predictions with the observed pattern of species richness in birds endemic to the continent. Latitudinal, longitudinal, and two-dimensional patterns of species richness are predicted well from the modeled null effects alone. As expected, null effects are of high significance for wide ranging species only. Our results highlight the conceptual significance of an until recently neglected constraint from continental shape alone and support a more cautious analysis of species richness patterns at this scale.

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Acknowledgments

W.J. thanks Andrew Rambaut, Oliver Pybus, and Pavel Stopka for vital C/C++ advice. Louis Hansen, on behalf of the Zoological Museum, University of Copenhagen, assisted us with access to the African bird database and provided the relevant updates we used. The manuscript benefited greatly from comments by two anonymous referees and from discussions with Paul Harvey, Mike Charleston, David Rogers, Rob Freckleton, Will Cresswell, Tom Romdal, Joslin Moore, Thomas Brooks, Bob May, and especially Robert Colwell. This work was supported by Deutscher Akademischer Austauschdienst, Natural Environment Research Council (London), and German Scholarship Foundation studentships (to W.J.).

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Information & Authors

Information

Published in

Go to Proceedings of the National Academy of Sciences
Go to Proceedings of the National Academy of Sciences
Proceedings of the National Academy of Sciences
Vol. 98 | No. 10
May 8, 2001
PubMed: 11344307

Classifications

Submission history

Received: December 15, 2000
Accepted: February 28, 2001
Published online: May 8, 2001
Published in issue: May 8, 2001

Acknowledgments

W.J. thanks Andrew Rambaut, Oliver Pybus, and Pavel Stopka for vital C/C++ advice. Louis Hansen, on behalf of the Zoological Museum, University of Copenhagen, assisted us with access to the African bird database and provided the relevant updates we used. The manuscript benefited greatly from comments by two anonymous referees and from discussions with Paul Harvey, Mike Charleston, David Rogers, Rob Freckleton, Will Cresswell, Tom Romdal, Joslin Moore, Thomas Brooks, Bob May, and especially Robert Colwell. This work was supported by Deutscher Akademischer Austauschdienst, Natural Environment Research Council (London), and German Scholarship Foundation studentships (to W.J.).

Authors

Affiliations

Walter Jetz
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom; and Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark
Carsten Rahbek
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom; and Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark

Notes

To whom reprint requests should be addressed. E-mail: [email protected].
Communicated by Richard Southwood, University of Oxford, Oxford, United Kingdom

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    Geometric constraints explain much of the species richness pattern in African birds
    Proceedings of the National Academy of Sciences
    • Vol. 98
    • No. 10
    • pp. 5371-5943

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