What determines conformity to Bergmann's rule?

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Aim: Bergmann's rule, the tendency of body size within species in bird and mammal populations to be positively correlated with latitude, is among the best known biogeographical generalizations. The factors behind such clines, however, are not well understood. Here we use a large data base of 79 mammalian carnivore species to examine the factors affecting latitudinal size clines. Location: Worldwide. Methods: We measured the skulls and teeth of carnivores in natural history museums, and calculated the amount of variation in size explained by latitude, supplementing our measurements with published data. We examined the effects of a number of variables on the tendency to show latitudinal clines. Results: We found that geographical range and latitudinal extent are strongly related to size clines. Minimum temperatures across the range, net primary productivity and habitat diversity also have some, albeit much less, influence. Main conclusions: We suggest that species with large geographical ranges are likely to encounter significant heterogeneity in those factors that influence body size, and are thus likely to exhibit size clines. However, the key factors that determine body size may not always operate along a latitudinal (or other geographical) cline, but be spatially linked to patches in the species range. One such important factor is likely to be food availability, which we show is a strong predictor of size in the brown bear (Ursus arctos) but is not associated with a latitudinal cline. We argue that the spatial distribution of key resources within the species range constitutes a significant predictor of carnivore body size.

Original languageEnglish
Pages (from-to)788-794
Number of pages7
JournalGlobal Ecology and Biogeography
Issue number6
StatePublished - Nov 2007


  • Body size
  • Carnivores
  • Clines
  • Food availability
  • Geographical variation
  • Latitude
  • Primary productivity
  • Rainfall
  • Range size
  • Temperature


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