great deal is now known about the neurohormonal mecha-
nisms of aggression and pairbonding in some rodents (e.g.,
voles), but we know almost nothing about how selection
favors these behaviors in various species with different
mating systems. Likewise, nearly ubiquitous sexual dimor-
phisms in social rodents, such as body size, timing of emer-
gence from hibernation, dispersal, and life spans have yet
to be adequately analyzed. We still do not understand the
function of dispersal, nor why natal dispersal occurs in
some species, postbreeding dispersal occurs in others, and
both types of dispersal (or neither type) occur in a few spe-
cies. And when dispersal occurs, why is it sometimes male
biased, sometimes female biased, and sometimes neither?
Of course, part of the problem is that some social behaviors
are nearly impossible to study in the field, including pa-
rental behavior, scent marking, facultative sex-ratio ad-
justment, reproductive suppression and activation, mate
choice, and social learning, whereas other social behaviors
are nearly impossible to study in the laboratory, includ-
ing social group formation, alarm calling, dispersal, and life
histories. Whereas it often is difficult to apply results of lab
studies to field situations, field studies often are unable to
control variables known from lab studies to be important.
Much also remains to be learned about rodent socioecol-
ogy. In particular, there is the perennial question of whether
group living (sociality) is a nonadaptive result of patchy dis-
tributions of critical resources, or is an adaptive response
due to advantages of foraging socially for widely scattered
and unpredictable food sources, or rapidly detecting and
effectively avoiding predators. The answer to this question
leads to different predictions about how the resulting group
or society will be structured and the types of social and re-
productive interactions that will occur (e.g., complex coop-
eration and reproductive skew may occur in the adaptive
case, but is not predicted in the nonadaptive case). Under-
standing the ecological causes of sociality are also impor-
tant for conserving and managing populations of rodents,
especially those that are threatened and endangered. For
example, rodents that group adaptively are more likely to
carry and transmit parasites and pathogens than are those
species that live in groups only when suitable habitats are
limited or patchy.
When rodent societies form because of advantages of liv-
ing near conspecifics, they are usually composed of close
kin. A question worth addressing is whether postweaning
young remain near home because of demographic bene-
fits of philopatry or costs of dispersal (e.g., safety, food), or
because there are inclusive fitness benefits to be derived
from assisting parents in raising siblings. Another interest-
ing question is the degree to which rodent societies are con-
vergent with those of other taxa. Conceptual analyses of so-
cial behavior remain sharply divided between schema that
attempt to differentiate cooperative breeding from euso-
ciality and those that view eusociality as part of a spectrum
of cooperative social systems. Although this distinction is
not explicitly taxonomic, proponents of the more restrictive
view typically regard eusociality as unique to insects, while
supporters of the more expansive view contend that pat-
terns of social structure transcend taxonomic boundaries,
and therefore apply to mammals and particularly to rodents
(e.g., African mole-rats, prairie dogs, beavers).
Chapters in this book reveal that, in general, ecologists
emphasize studies of rodent populations, communities, and
population-level outcomes of behaviors, but sometimes they
lose sight of the individual. Psychologists are particularly
good at teasing apart cognitive processes and develop-
mental ontogenies of individuals, but sometimes they are
unaware of fitness outcomes, or use of the comparative
method to infer evolutionary histories. Physiologists have
taught us much about rodent behavioral mechanisms, and
geneticists have elucidated the details of genetic mecha-
nisms of rodents, but sometimes these biologists are not
completely aware of the environmental influences, fitness
consequences, or evolutionary histories of the mechanisms
they have discovered. Conservation biologists investigate
population numbers and distributions, habitat choices and
resource needs, but they sometimes ignore the importance
of social behaviors when developing management plans.
And behavioral ecologists specialize in studying rodent so-
ciobiology in nature, but they sometimes are oblivious to
the underlying mechanistic and developmental constraints
on those behaviors. Bridging these gaps and preconcep-
tions, and expansion of our knowledge, will require new
programs of collaborative research. There are exciting pos-
sibilities here, because scientific fields often grow most rap-
idly at their intersections. We suggest that a modest and
worthy goal over the next decade would be a collaborative
effort to thoroughly investigate and achieve a complete un-
derstanding of just one social behavior (e.g., alarm calling,
infanticide, alloparental care, sex-ratio adjustment) in one
social rodent species at all four levels of analysis.
In our introduction to this anthology we explained its
conception, scope, and intended audience. We expressed
the hope that this book would contribute not only to a bet-
ter understanding of the social biology of rodents but also
to evolutionary and ecological theory in general. The extent
to which the editors and authors have been successful in
meeting those goals are up to you and future generations to
decide. At this point, we wish to express three final hopes:
that you have enjoyed reading Rodent Societies,that at least
one chapter has touched you personally and professionally,
and that as a result you, your colleagues and students, and
your institutional libraries will find it to be a valuable ref-
erence for many years to come.490 Chapter Forty-Two