ABSTRACT
Ursids are the largest mammals to retain a plantigrade posture. This primitive posture has been proposed to result in reduced locomotor speed and economy relative to digitigrade and unguligrade species, particularly at high speeds. Previous energetics research on polar bears (Ursus maritimus) found locomotor costs were more than double predictions for similarly sized quadrupedal mammals, which could be a result of their plantigrade posture or due to adaptations to their Arctic marine existence. To evaluate whether polar bears are representative of terrestrial ursids or distinctly uneconomical walkers, this study measured the mass-specific metabolism, overall dynamic body acceleration, and gait kinematics of polar bears and grizzly bears (Ursus arctos) trained to rest and walk on a treadmill. At routine walking speeds, we found polar bears and grizzly bears exhibited similar costs of locomotion and gait kinematics, but differing measures of overall dynamic body acceleration. Minimum cost of transport while walking in the two species (2.21 J kg−1 m−1) was comparable to predictions for similarly sized quadrupedal mammals, but these costs doubled (4.42 J kg−1 m−1) at speeds ≥5.4 km h−1. Similar to humans, another large plantigrade mammal, bears appear to exhibit a greater economy while moving at slow speeds.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: A.M.P., T.M.W.; Methodology: A.M.P., T.M.W.; Formal analysis: A.M.P.; Investigation: A.M.P., C.T.R., T.M.W.; Data curation: A.M.P., A.M.C., C.T.R., T.B., N.W., N.N., A.H., T.M.W.; Writing - original draft: A.M.P.; Writing - review & editing: A.M.P., A.M.C., C.T.R., M.A.O., T.M.W.; Supervision: C.T.R., M.A.O., A.C., T.M.W.; Project administration: C.T.R., M.A.O., T.M.W.; Funding acquisition: A.M.P., C.T.R., M.A.O., A.C., T.M.W.
Funding
Support was provided by the U.S. Geological Survey’s Changing Arctic Ecosystems Initiative, Polar Bears International, the North Pacific Research Board, Interagency Grizzly Bear Committee, fRI Research, the Raili Korkka Brown Bear Endowment, the Bear Research and Conservation Endowment, the Nutritional Ecology Endowment, Washington State University, San Diego Zoo Global, Oregon Zoo, SeaWorld and Busch Gardens Conservation Fund, University of California, Santa Cruz, and the International Association for Bear Research and Management. Funding was also provided by National Science Foundation DBI 1255913-015 (to T.M.W.).
Data availability
Data reported in this paper are archived in the USGS Science Data Catalog: https://doi.org/10.5066/F7QR4W91 and https://doi.org/10.5066/F7XW4H0P.
Supplementary information
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.175372.supplemental
- Received December 2, 2017.
- Accepted April 21, 2018.
- © 2018. Published by The Company of Biologists Ltd
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