As this synopsis suggests, the approaches used to explore
the adaptive bases for group living have differed between
studies of octodontids and ctenomyids, with the former
making greater use of experimental manipulation of natu-
ral and laboratory environments and the latter emphasizing
long-term monitoring of free-living populations. Clearly,
both methodological approaches are important, and both
yield critical information regarding potential causes of so-
ciality in these animals. Future studies of these and other
rodent species will benefit from an integrated research strat-
egy that combines observational studies of behavior, ecol-
ogy, and demography with experimental manipulations of
relevant environmental variables. Analyses of the adaptive
bases for sociality in cururos are just beginning and, hence,
this species provides an ideal opportunity to pursue a com-
prehensive research program aimed at identifying intrinsic
as well as extrinsic factors that favor group living.
Potential Life-History Correlates
Although the Octodontidae and Ctenomyidae are sister
families (Honeycutt chap. 2 this volume), as discussed pre-
viously in this chapter, they appear to have followed quite
different evolutionary trajectories in terms of phyletic, eco-
logical, and morphological differentiation. This marked
variation among otherwise relatively closely related species
provides an unusual opportunity to explore how variability
in the basic life-history traits of octodontids and ctenomy-
ids may have contributed to their differential tendency to
live in groups. Salient life-history attributes of these animals
that may influence sociality include the following:Production of precocial young
Like other hystricognath rodents, octodontids and cteno-
myids give birth to relatively precocial young (Weir 1974;
Künkele and Trillmich 1997). This is in marked contrast
to sciurognath rodents, most of which produce altricial off-
spring (Ferron 1984). Although the social consequences of
this life history variation have not been explored in detail,
it has been suggested that group living may be favored in
species with more precocial young. Specifically, group de-
fense or babysitting of neonates may be particularly benefi-
cial in species in which pups quickly become mobile yet re-
main vulnerable to predators (Kleiman 1974).Predicted relationships between precociality and sociality
The predator protection hypothesis suggests that within the
Octodontidae and Ctenomyidae there should be a posi-
tive relationship between precociality and degree of social-
ity. By extension, between families, precociality should be
more pronounced among octodontids, in which sociality
appears to be more common.Available evidence
Within the Ctenomyidae, the degree of precociality appears
to vary among the few species for which appropriate data412 Chapter Thirty-Four
Figure 34.5 Summary of proposed life history correlates of sociality in octodontid and ctenomyid rodents. For each
hypothesis, the relevant life-history trait is indicated, as is the primary adaptive benefit of sociality and the predicted rela-
tionship with social structure.