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!


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