the rodent taxa themselves. One understudied perspective
is the effects of climatic variation on sexual size dimor-
phism. Evidence indicates that climate can have profound
effects on the evolution of body size and sexual dimorphism.
Chipmunks generally exhibit female-biased sexual dimor-
phism, and it has been hypothesized that climate may play
a role in the evolution of this pattern of body size. Using cli-
mate normals and published data on body size of male and
female chipmunks from 40 populations (11 species), I used
multiple regression analysis to determine which climatic
variables influence the magnitude of sexual dimorphism.
The degree of female-biased sexual dimorphism declined
with increasing annual rainfall and low winter tempera-
tures, indicating that extreme climatic conditions may in-
fluence female size and reproductive energetics. Although
much research on mammals has focused on male-biased
sexual dimorphism and the role of sexual selection on male
size, a more integrated approach examining selection on
body size in both sexes will lead to a more complete under-
standing of the evolution of sexual dimorphism in rodents.128 Chapter Ten