- Offspring should benefit by dispersal of parents through
increased chances of survival and reproduction (sensu
Jones 1986).
Lambin (1997) reviewed territory bequeathal studies and
concluded that most of this information was anecdotal. We
reexamined the studies reviewed by Lambin (1997), elimi-
nating those that did not pertain directly to the three criti-
cal predictions of the territory bequeathal hypothesis. Of
the 16 remaining rodent studies, offspring did not remain
in the natal territory for long after weaning in two studies,
there was no support for the territory bequeathal hypothe-
sis in six studies, and there was support for the territory be-
queathal hypothesis in the eight (50%) remaining studies.
The best evidence in favor of the territory bequeathal hy-
pothesis comes from studies of Columbian ground squirrels
(Harris and Murie 1984), red squirrels (Price and Boutin
1993; Berteaux and Boutin 2000), and banner-tailed kan-
garoo rats (Dipodomys spectabilis,Jones 1986). Breeding
dispersal by female Columbian ground squirrels was most
likely to occur when a yearling daughter was still present
on the natal territory (females dispersed in 11 of 17 [65%]
cases when daughters were present, compared to 8 of 32
[25%] when no daughter was present). Yearling females
tended to remain on the territories held by their mothers
during the previous year. There was also a nonsignificant
tendency for daughters to be more reproductively success-
ful if their mother dispersed from the natal territory and
they remained (8 of 11 [73%] as compared to only 2 of 6
[33%] whose mothers did not disperse). In red squirrels,
more breeding females (7 of 28 [25%]) than nonbreeding
females (0 of 14) dispersed. More young females survived
on their natal territory after the mother had dispersed (97
of 119 [81.5%]) compared to young females that obtained
another territory with a midden (56 of 96 [58.3%]) or those
that did not obtain a territory with a midden (95 of 164
[57.9%]). These data support all three predictions of the
territory bequeathal hypothesis.
Remain philopatric and cooperate
Some adult females and offspring remain at or near the na-
tal nest. Hypotheses proposed to explain the occurrence of
natal philopatry have emphasized costs of dispersal on the
one hand and benefits of philopatry on the other (Koenig
et al. 1992). Three main factors have received the most at-
tention: (1) life-history variables — certain taxa are predis-
posed to remain philopatric due to life-history traits (Ar-
nold and Owens 1998; Pen and Weissing 2000; Kokko and
Lundberg 2001), (2) ecological constraints — individuals
delay dispersal and remain philopatric because costs of
dispersal are prohibitive (Brown 1974; Koenig and Pitelka
1981; Emlen 1982; Jarvis et al. 1994; Koenig et al. 1992),
and (3) benefits of philopatry — individuals delay dispersal
and remain philopatric because they gain direct or indirect
fitness benefits (Stacey and Ligon 1987, 1991; Kokko and
Johnstone 1999). These hypotheses are complementary,
because costs and benefits, as well as life-history factors,
affect dispersal (see Emlen 1994; Solomon 2003; Nunes,
chap. 13, this volume for further discussion on dispersal
and philopatry).Female kin clusters
Female philopatry often results in adult female kin living
in close spatial proximity to each other (Michener 1983a;
Vestal and McCarley 1984; Smith 1993; Solomon 2003;
fig. 4.2). The formation of female kin clusters has been doc-
umented in a variety of rodents, including numerous species
of ground squirrels (Vestal and McCarley 1984; Yensen and
Sherman 2003), black-tailed prairie dogs (Hoogland 1995),
yellow-bellied marmots (Armitage and Schwartz 2000),
gray squirrels (Sciurus carolinensis; Koprowski 1996),
Townsend’s voles (Microtus townsendii,Lambin and Yoc-
coz 1998), and house mice (Dobson and Baudoin 2002).
Having kin as neighbors may be beneficial because it cre-
ates the opportunity for nepotistic interactions between in-
dividuals that may enhance their inclusive fitness. Types
of potentially nepotistic behaviors that may contribute to
greater reproductive success for females living in kin clus-
ters include reduced aggression among relatives (e.g., Char-
nov and Finerty 1980; Sherman 1980a; Michener 1981;
McClean 1982), sharing of space (e.g., Sherman 1981a;
Vestal and McCarley 1984; Mappes et al. 1995; Lambin
and Yoccoz 1998), cooperative defense against predators54 Chapter Four
Figure 4.2 Natal philopatry by females can result in the formation of female
kin clusters. Having kin as neighbors creates the opportunity for selection favor-
ing nepotistic behaviors, which may lead to the evolution of cooperative breed-
ing among related females. Figure courtesy of Christine R. Maher.