Variation in North American ermine (Mustela erminea)
In western North America, least weasels
(ermine) exhibit a marked latitudinal gradient, with larger animals found
in the more northerly parts of the range. The map indicates the origins
of each of the skulls: each represents a different subspecies. The trend
is an example of Bergman's Rule.
Text material © 2005 by Steven M. Carr