Is spatial variation in food availability an explanation for a Bergmannian size pattern in a North American hibernating, burrowing mammal? An information-theoretic approach

WOS: 000304300300004Predictable empirical patterns of variation in body size along spatial and environmental gradients have been documented within many species of mammals. Four main hypotheses, heat conservation, heat dissipation, primary productivity and seasonality, have been proposed to explain these patterns of variation in body size. In this study, we reported an analysis of geographic variation in body size of Richardson's ground squirrels Urocitellus richardsonii, a North American hibernating, burrowing mammal. Firstly, we evaluated whether a Bergmannian size pattern was exhibited by Richardson's ground squirrels. Secondly, we used an information-theoretic approach to test which of the four main hypotheses best explain(s) geographic variation in body size of Richardson's ground squirrels or to assess whether, as proposed by McNab's resource rule or Huston and Wolverton's eNPP rule, the primary productivity hypothesis is the only explanation. Richardson's ground squirrels exhibited a pattern of increasing body size towards the colder areas, that is, more productive and seasonal central Alberta and foothills of the southern Alberta Rocky Mountains, indicative of a Bergmannian size pattern. Plant productivity and seasonality in plant productivity were likely the primary underlying factors generating the observed pattern of geographic variation in body size. Thus, our results supported primary productivity and seasonality hypotheses. From these results, we see that McNab's resource rule or Huston and Wolverton's eNPP rule (i.e. spatial variation in food availability) is an explanation for a Bergmannian size pattern in Richardson's ground squirrels, but not the only explanation.University of Lethbridge; Ahi Evran UniversityAhi Evran UniversityWe thank M. A. Edwards and B. Weimann of the Royal Alberta Museum, Edmonton, Alberta, Canada, for the permission to use information recorded for specimens of Richardson's ground squirrels in the museum collection; G. R. Michener and anonymous reviewers for providing detailed and helpful comments on the paper; C. Karacaoglu for helping in obtaining the normalized difference vegetation index data; and U. Perktas for drawing Fig. 1. H. G. contributed to all aspects of the study and M. K. G. primarily to the interpretations of the results of the study, especially in terms of hibernation ecology. H. G. (supported by the University of Lethbridge Postdoctoral Fellowship in Terrestrial Ecology and Ahi Evran University) and M. K. G. (supported by Ahi Evran University) conceived the idea for the study while conducting postdoctoral studies under the supervision of G. R. Michener in the Department of Biological Sciences at the University of Lethbridge, Alberta, Canada