of their lives, the same neighbors may share overlapping
areas for extended periods (Zeng and Brown 1987; Jones
1989; Randall 1989b). Dipodomys merriamiare philopat-
ric; individuals living near each other may be related, so
that most pilferers are close kin. For all these reasons, the
benefit of chasing conspecifics does not seem worth the
costs in time, energy, and water loss that would result from
social intolerance.
In contrast, the larger-sized species of kangaroo rats are
highly territorial within and between sexes. Although ter-
ritoriality often evolves for reasons other than defense of
food, such as to prevent infanticide (Wolff and Peterson
1998), these larger-sized kangaroo rats store food in defen-
sible caches. Both males and females store seeds in a larder
in a defined burrow area, and they actively defend the area
from other kangaroo rats by chasing and footdrumming
(Randall 1993). The larger body size allows the kangaroo
rats to dig and manage burrow areas for their seed caches
that might be less economically feasible for the smaller-
sized species.
Dipodomys desertiis the most territorial and intolerant
species of kangaroo rat studied thus far. The lack of so-
cial tolerance is probably related to the harshness of the en-
vironment and competition for scarce resources in a sand
dune habitat that has limited space to construct burrows,
and limited seed production (Sullivan 2000). Competition
is intense — the kangaroo rats often visit neighboring terri-
tories in attempts to enter burrows to pilfer seeds (Randall
1997; Sullivan 2000; Randall and Boltas King 2001). Ago-
nistic interactions are frequent; the territorial owner usually
responds by rushing the visitor and chasing aggressively, of-
ten until contact is made and a rollover fight ensues.Role of familiarity and social tolerance in kangaroo rats
Familiarity and neighbor recognition play important roles
in the maintenance of spacing and social order in several
species of kangaroo rat (D. merriami;Randall 1989b; D.
ordii;Perri and Randall 1999; D. ingens;Murdock and
Randall 2001; D. spectabilis;Randall 1989c). Familiarity
is independent of the type of spacing, and species such as
D. merriamiin overlapping home ranges and D. spectabilis
and D. ingensin individual territories recognize and toler-
ate familiar neighbors more than unfamiliar strangers.
Social experience and familiarity apparently are impor-
tant in coordinating the mating interactions of kangaroo
rats. Female D. heermannihoused in social isolation exhib-
ited longer estrous cycles that were disrupted for months
compared with females housed under conditions in which
they could see and smell conspecifics (Yoerg 1999). Female
D. merriami, D. ordii, D. spectabilis,and D. ingensprefer
the scent of familiar males (Randall 1993; Murdock and
Randall 2001), and females tolerate and interact with fa-
miliar males more than with unfamiliar males in paired en-
counters and during mating (Randall 1989b, 1989c, 1991a;
Perri and Randall 1999; Randall et al. 2002). Before mat-
ing, males spend considerable time in the home area of es-
trous females, probably to establish familiarity.Environmental Constraints and the Evolution of Sociality in Semifossorial Desert Rodents 375Table 31.3 Comparison of size and percentage overlap of homes ranges for six species of Dipodomy,
ranging from the largest body mass to the smallestHome range overlap (%)
Home range (ha) Opposite Same sex
sex (male
Species Male Female on female) Male FemaleD. ingens July –Aug. 0.02 0.02 12.1 0.3 48.6a
Feb.–Marchb 0.10 0.02 63.3 19.3 0
D. spectabilis 0.05c 0.05 2 2 2
D. deserti March–Aprilb 0.18 0.12 3.5 2 1
Nov.–Dec.d 0.08 0.13 6.69 16.62 8.86
D.heermannib 0.11 0.04 16.8 10.7 1.3
D.ordiib,e 0.07 0.07 25.4 9.9 3.14
D.merriami Californiab,f 0.34 0.31 22.2 16.2 10.4
Arizonab,e 0.17 0.07 50.7 20.7 8.12aOverlapping cluster of five females in nonbreeding season.
bBreeding season.
cEstimate without regard to sex.
dBeginning of breeding; density increased from 4.4/ha to 6.4/ha.
eHigh density.
fData from three periods combined.
SOURCE: For D. ingens:Cooper 2002. For D. spectabilis:Schroder 1979. For D. deserti:Sullivan 2000. For D. heermanni:Shier and
Randall 2004. For D. merriami:in California, Behrends et al. 1986; in Arizona, Perri and Randall 1999.