no relationship between paternal care and relative litter
weight. Although there was a relationship between male
spacing behavior and relative litter weight, it was in the op-
posite direction to the prediction of Ribble (2003). Males of
species with relatively low litter weights tended to be mo-
nogamous, suggesting that maternal investment in offspring
(as measured by relative litter weight) may not necessitate
male parental care.
Paternal care has evolved six times within the Neotomine-
Peromyscine clade. This is consistent with the conclusions
of Ribble (2003) that paternal care evolved more than once
within Peromyscus. Comparing the evidence for male care
to male spacing, we found a relationship between these two
characters, with monogamously spaced males tending to
provide paternal care. Thus across the entire clade, male
care may be associated with monogamy, but there is little
known about the social behavior of many species (e.g.,Neo-
tomodon). These results suggest that male care may play
a role in the evolution and maintenance of monogamy,
and support the field experiments of Gubernick and Teferi
(2000). These results are inconsistent with more global
analyses (e.g., Komers and Brotherton 1997) that suggest
that mammalian monogamy is not related to paternal care,
but rather to female spacing and mate guarding. Whether
the Neotomine-Peromyscine taxa are different from other
mammals awaits more complete descriptions of social be-
havior from more taxa.
We found that the size of a species distributional range
was related to breeding behavior and litter size. Consistent
with findings of Glazier (1980), we found that litter size
of Neotomine-Peromyscine rodents increased with the dis-
tributional range of a species. Furthermore, monogamous
males and males that exhibited paternal care of offspring
were from species with relatively small distribution ranges.82 Chapter Six
C
Figure 6.6 (continued)