Rule reversal: Ecogeographical patterns of body size variation in the common treeshrew (Mammalia,Scandentia) |
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Authors: | Eric J. Sargis Virginie Millien Neal Woodman Link E. Olson |
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Affiliation: | 1. Department of Anthropology, Yale University, New Haven, CT, USA;2. Division of Vertebrate Zoology, Yale Peabody Museum of Natural History, New Haven, CT, USA;3. Redpath Museum, McGill University, Montreal, QC, Canada;4. United States Geological Survey, Patuxent Wildlife Research Center, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA;5. University of Alaska Museum, University of Alaska Fairbanks, Fairbanks, AK, USA |
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Abstract: | There are a number of ecogeographical “rules” that describe patterns of geographical variation among organisms. The island rule predicts that populations of larger mammals on islands evolve smaller mean body size than their mainland counterparts, whereas smaller‐bodied mammals evolve larger size. Bergmann's rule predicts that populations of a species in colder climates (generally at higher latitudes) have larger mean body sizes than conspecifics in warmer climates (at lower latitudes). These two rules are rarely tested together and neither has been rigorously tested in treeshrews, a clade of small‐bodied mammals in their own order (Scandentia) broadly distributed in mainland Southeast Asia and on islands throughout much of the Sunda Shelf. The common treeshrew, Tupaia glis, is an excellent candidate for study and was used to test these two rules simultaneously for the first time in treeshrews. This species is distributed on the Malay Peninsula and several offshore islands east, west, and south of the mainland. Using craniodental dimensions as a proxy for body size, we investigated how island size, distance from the mainland, and maximum sea depth between the mainland and the islands relate to body size of 13 insular T. glis populations while also controlling for latitude and correlation among variables. We found a strong negative effect of latitude on body size in the common treeshrew, indicating the inverse of Bergmann's rule. We did not detect any overall difference in body size between the island and mainland populations. However, there was an effect of island area and maximum sea depth on body size among island populations. Although there is a strong latitudinal effect on body size, neither Bergmann's rule nor the island rule applies to the common treeshrew. The results of our analyses demonstrate the necessity of assessing multiple variables simultaneously in studies of ecogeographical rules. |
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Keywords: | Bergmann's rule geographical variation island area island rule latitude Malay Peninsula mammals sea depth Southeast Asia
Tupaia glis
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