Latitudinal variation in snowshoe hare (Lepus americanus) body mass: A test of bergmann’s rule

Laura C. Gigliotti, Nathan D. Berg, Rudy Boonstra, Shawn M. Cleveland, Duane R. Diefenbach, Eric M. Gese, Jacob S. Ivan, Knut Kielland, Charles J. Krebs, Alexander V. Kumar, L. Scott Mills, Jonathan N. Pauli, H. Brian Underwood, Evan C. Wilson, Michael J. Sheriff

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


The relationship between body size and latitude has been the focus of dozens of studies across many species. However, results of testing Bergmann’s rule — that organisms in colder climates or at higher latitudes possess larger body sizes — have been inconsistent across studies. We investigated whether snowshoe hares (Lepus americanus Erxleben, 1777) follow Bergmann’s rule by investigating differences in body mass using data from six published studies and from data of 755 individual hares captured from 10 populations across North America covering 26° of north latitude. We also explored alternative hypotheses related to variation in hare body mass, including winter severity, length of growing season, elevation, and snow depth. We found body mass of hares varied throughout their range, but the drivers of body mass differed based on geographic location. In northern populations, females followed Bergmann’s rule, whereas males did not. In northern populations, male mass was related to mean snow depth. In contrast, in southern populations, body mass of both sexes was related to length of the growing season. These differences likely represent variation in the drivers of selection. Specifically, in the north, a large body size is beneficial to conserve heat because of low winter temperatures, whereas in the south, it is likely due to increased food supply associated with longer growing seasons.

Original languageEnglish
Pages (from-to)88-95
Number of pages8
JournalCanadian Journal of Zoology
Issue number2
StatePublished - 2020


  • Energy expenditure
  • Food supply
  • Growing season
  • Latitudinal variation
  • Lepus americanus
  • Snow depth
  • Snowshoe hare
  • Winter


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