systems. For example, growth and development tend to oc-
cur over a longer time period in large-bodied compared to
small-bodied sciurids, and dispersal and sexual matura-
tion tend to be delayed in many large-bodied species, re-
sulting in prolonged residence in the natal area. Armitage
(1981) noted that kin selection favors cooperative interac-
tions among relatives living together, which can promote
complex social organization. An association between large
body size, delayed maturity and dispersal, and complex so-
cial systems has been observed in a variety of sciurids, in-
cluding yellow-bellied marmots, Gunnison’s prairie dogs
(Cynomys gunnisoni), and black-tailed prairie dogs (Armi-
tage 1981; Downhower and Armitage 1981; Rayor 1985;
Garrett and Franklin 1988; Blumstein and Armitage 1999).
Michener (1983a) also suggested that philopatry and coop-
eration among female kin were important in the evolution
of sociality in ground-dwelling sciurids.
Philopatry and delayed dispersal are also associated with
complex social organization in common mole-rats, Dama-
raland mole-rats, and naked mole-rats. These species have
complex social organization, and individuals of the species
act cooperatively to forage and raise young (Solomon 1991;
Spinks et al. 1999; Burda et al. 2000; Molteno and Bennett
2002).ConclusionsRodent studies have greatly contributed to our understand-
ing of the ultimate and proximate causes and consequences
of dispersal and philopatry (figs. 13.5 and 13.6). Although
competition for mates and environmental resources un-
doubtedly influence dispersal behavior, inbreeding avoid-
ance appears to provide the most general evolutionary in-
fluence favoring sex-biased natal dispersal. Inbreeding
depression is potentially costly (Ralls et al. 1988; Lacy et al.
1993), and leaving the natal area to find unrelated mates
seems to be a common strategy among rodents for enhanc-160 Chapter Thirteen
Figure 13.5 A model of male-biased natal dispersal in mammals based on studies of rodents.