Cooperation and individuality among man-eating lions
Edited by Kristen Hawkes, University of Utah, Salt Lake City, UT, and approved September 25, 2009
Abstract
Cooperation is the cornerstone of lion social behavior. In a notorious case, a coalition of two adult male lions from Tsavo, southern Kenya, cooperatively killed dozens of railway workers in 1898. The “man-eaters of Tsavo” have since become the subject of numerous popular accounts, including three Hollywood films. Yet the full extent of the lions' man-eating behavior is unknown; estimates range widely from 28 to 135 victims. Here we use stable isotope ratios to quantify increasing dietary specialization on novel prey during a time of food limitation. For one lion, the δ13C and δ15N values of bone collagen and hair keratin (which reflect dietary inputs over years and months, respectively) reveal isotopic changes that are consistent with a progressive dietary specialization on humans. These findings not only support the hypothesis that prey scarcity drives individual dietary specialization, but also demonstrate that sustained dietary individuality can exist within a cooperative framework. The intensity of human predation (up to 30% reliance during the final months of 1898) is also associated with severe craniodental infirmities, which may have further promoted the inclusion of unconventional prey under perturbed environmental conditions.
Acknowledgments.
We thank A. K. Behrensmeyer, E. E. Butler, C. E. Chow, C. T. Darimont, J. A. Estes, L. Gahegan, P. Hluzova, J. B. Hopkins, S. D. Newsome, J. D. Phelps, J.W. Ridges, W. Stanley, R. H. Tuttle, E. R. Vogel, P. V. Wheatley, and C. C. Wilmers for helpful comments and discussions. We thank the Duckworth Laboratory, the Field Museum of Natural History, and the Smithsonian National Museum of Natural History for access to unpublished field reports. Modern samples were imported under CITES import no. US-012 (PRT 701716). This study was approved by the Chancellor's Animal Research Committee of University of California (UC)-Santa Cruz (no. Domin0806) and approved as exempt by the Institutional Review Board of UC-Santa Cruz (no. HS0801187). This study was funded by the Earthwatch Institute, the David and Lucile Packard Foundation, and a grant from the UC-Santa Cruz Committee on Research.
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Cover image: Pictured are two adult male lions from the Tsavo region, Southern Kenya. This pair bears a physical resemblance to two Tsavo lions that were known for their cooperative man-eating behaviors in 1898. Justin D. Yeakel et al. present isotopic evidence that reveals individual dietary specialization within the historical lion dyad, including the extent of human depredation, and suggest that such aberrant behavior was the result of the lions' physical infirmity combined with environmental and anthropogenic stressors. See the article by Yeakel et al. on pages 19040–19043. Image by Bruce D. Patterson.
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© 2009.
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Received: May 13, 2009
Published online: November 10, 2009
Published in issue: November 10, 2009
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Acknowledgments
We thank A. K. Behrensmeyer, E. E. Butler, C. E. Chow, C. T. Darimont, J. A. Estes, L. Gahegan, P. Hluzova, J. B. Hopkins, S. D. Newsome, J. D. Phelps, J.W. Ridges, W. Stanley, R. H. Tuttle, E. R. Vogel, P. V. Wheatley, and C. C. Wilmers for helpful comments and discussions. We thank the Duckworth Laboratory, the Field Museum of Natural History, and the Smithsonian National Museum of Natural History for access to unpublished field reports. Modern samples were imported under CITES import no. US-012 (PRT 701716). This study was approved by the Chancellor's Animal Research Committee of University of California (UC)-Santa Cruz (no. Domin0806) and approved as exempt by the Institutional Review Board of UC-Santa Cruz (no. HS0801187). This study was funded by the Earthwatch Institute, the David and Lucile Packard Foundation, and a grant from the UC-Santa Cruz Committee on Research.
Notes
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0905309106/DCSupplemental.
Authors
Competing Interests
The authors declare no conflict of interest.
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