mer 2000). Further evidence of monogamy in this spe-
cies includes sexual monomorphism, small testes size, and
single-male paternity (Sommer and Tichy 1999; Sommer
2000).
Monogamous pairs may also recruit helpers to provide
additional parental behavior to maximize offspring survival.
Most Eurasian marmots (Marmotaspp.) are cooperative
breeders, with only a single alpha pair breeding (Allaine
2000). This strategy (monogamy and cooperative breeding)
may have evolved as an adaptation to harsh environments,
in which group hibernation gives a thermal advantage and
increases offspring survival (Allaine 2000; see also Armi-
tage, chap. 30, this volume). Thermoregulation and coop-
erative maintenance of territories has been suggested as
the main benefit of grouping and monogamy in Cape por-
cupines (Hystrix africaeaustralis;Corbet and van Aarde
1996).
Facultative monogamy
Monogamy has also arisen in species of rodents in which
males do not contribute paternal care, but may be unable
to access more than one mate because females or other re-
sources are spatially dispersed (Kleiman 1977; Komers and
Brotherton 1997; Ribble 2003). Mating patterns within
32 Chapter Three
Figure 3.1 Constraints on male mating success (ovals) that lead to different
mating systems (diamonds, bold) and male mating strategies (boxes).
Figure 3.2 Examples of obligate monogamy: (a) California mouse, faculta-
tive monogamy, (b) prairie vole, and polygyny/promiscuity (c) gray-tailed voles.
Photo of California mouse © David J. Gubernick; prairie vole and gray-tailed
vole © J. Wolff.ABC