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The Scientific World Journal
Volume 2014, Article ID 643694, 12 pages
Research Article

Body Size Mediated Coexistence in Swans

1Appalachian Laboratory, University of Maryland Center for Environmental Science, Frostburg, MD 21532-2307, USA
2Department of Biology, Syracuse University, Syracuse, NY 13244-1270, USA
3Department of Mathematics and Statistics, Utah State University, Logan, UT 84322-3900, USA

Received 28 August 2013; Accepted 24 October 2013; Published 4 February 2014

Academic Editors: R. Julliard and S. Rossi

Copyright © 2014 Katharina A. M. Engelhardt et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Differences in body sizes may create a trade-off between foraging efficiency (foraging gains/costs) and access to resources. Such a trade-off provides a potential mechanism for ecologically similar species to coexist on one resource. We explored this hypothesis for tundra (Cygnus columbianus) and trumpeter swans (Cygnus buccinator), a federally protected species, feeding solely on sago pondweed (Stuckenia pectinata) tubers during fall staging and wintering in northern Utah. Foraging efficiency was higher for tundra swans because this species experienced lower foraging and metabolic costs relative to foraging gains; however, trumpeter swans (a) had longer necks and therefore had access to exclusive resources buried deep in wetland sediments and (b) were more aggressive and could therefore displace tundra swans from lucrative foraging locations. We conclude that body size differentiation is an important feature of coexistence among ecologically similar species feeding on one resource. In situations where resources are limiting and competition for resources is strong, conservation managers will need to consider the trade-off between foraging efficiency and access to resources to ensure ecologically similar species can coexist on a shared resource.