or rocky substrate for one reason or another (fig. 35.1). This
figure includes genera that sometimes live in rocky habitat
(Ototylomys;big-eared climbing rats andCardiocranius;
five-toed dwarf jerboas); den in caves or crevices (Petau-
rista;giant flying squirrels and Erethizon;North Ameri-
can porcupine); dig burrows under rocks or shelter among
rocks (Ichthyomys;fish-eating rats and Selevinia;desert
dormice); have been collected among rocks (Vernaya;Ver-
nay’s climbing mice and Diomys;Crump’s mouse), and oth-
ers. Although expansive, the list in figure 35.1 is certainly
not exhaustive, as some genera like Marmotacontain spe-
cies that are clearly associated with rocks and boulders
(Tyser 1980), yet the generic account in Nowak (1991) did
not mention this association. Regardless, figure 35.1 illus-
trates the extensive diversity of rodents that utilize rocky
substrate. What is it about rocks that make them such an
essential component of the habitat for so many rodents?
Why Live in Rocky Habitat?
Complex nature of the habitat
In its broadest sense, rocky habitat may be described as any
locality that contains boulders, rocks, scree, pebbles, out-
crops, cliffs, or caves. Rocky substrate may extend without
interruption across the landscape, as exemplified by the
continuous mountain ranges of south-central Tunisia in-
habited by common gundis (Ctenodactylus gundi) and ele-
phant shrews (Elephantulus rozeti;K. Nutt, pers. obs.), or
may be clumped and isolated, such as the disjunct Seren-
geti kopjes of bush and rock hyrax (Heterohyrax bruceiand
Procavia johnstoni,respectively; Hoeck 1982; Gerlach and
Hoeck 2001). One of the reasons why so many rodents
live in rocky habitat is because it is topographically very
complex, containing a multitude of crevices and cavities
in which animals can nest, seek shelter, and find shade
(George 1986; Trainor et al. 2000). Studies of the ecol-
ogy and behavior of rock-dwelling mammals have provided
valuable insight into how such topographically complex
habitat is partitioned (George and Crowther 1981; Chan-
ning 1984; Etheredge et al. 1989; Trainor et al. 2000; Jones
et al. 2001). For example, in South Africa the namtap
(Graphiurus ocularus) is able to share its rocky habitat with
both Namaqua rock rats (Aethomys namaquensis) and ele-
phant shrews (Elephantulus edwardii) because the namtap
preferentially makes use of vertical rock crevices, whereas
the other two species use horizontal crevices (Channing
1984). In the rock formations of Israeli deserts, a difference
in diel cycle allows two spiny mice (Acomyssp.) to coexist
(Jones et al. 2001). In many rocky habitats, smaller-bodied
rock-dwelling rodents coexist with larger-bodied mammals418 Chapter Thirty-Five
Figure 35.1 Number of genera within each rodent family that contain at least one species that utilizes rocky substrate
(gray bars) or contain only species that do not associate with rocks (black bars). Data were compiled from generic accounts
in Nowak (1991). Not shown are the eleven rodent families that do not contain any genera that associate with rocks.