SOCIAL AND
ECOLOGICAL RELATIONS BETWEEN SPECIES
While most
non-human primates belong to just
one group at a time, there are some, including the African guenons,
that
habitually belong to more than one group, as their group of
conspecifics
associates regularly with a group belonging to a different species.
When
mixed-species association is variable in its occurrence, one has an
excellent
study system in which to evaluate the ultimate or evolutionary reasons
for
group living. A study of the function of such associations
between
blue monkeys and the closely related and sympatric redtail monkeys (C.
ascanius) was the subject of my first book. Based again on
field
observations, I was able to show that the two species involved
experience
various costs and benefits from their mutual associations, that these
costs
and benefits were not the same for the two species, and that the
species
that appeared to derive the greatest net gain was also most responsible
for
maintaining associations with its partner. A detailed comparison
of
my results with more limited information from another study site
supported
the original conclusions.
There are
opportunities here for further
research. The hypotheses I developed that relate ecological
factors to mixed-species association need to be tested with fresh
observations. In addition, there remain interesting
questions related to the behavioral mechanisms (such as vocalizations)
that ensure coordination between species. Paul Buzzard's
dissertation work on
interspecific relations in guenons of the Tai Forest, Cote d'Ivoire,
showed that relations between species, even guenon species, can be
quite different in different forests. Finally, large scale comparisons
to other taxonomic groups, such as cetaceans, are in their infancy!