(M.A. Conservation Biology 2010)
Mixed-Species Associations of Blue Monkeys (Cercopithecus mitis) and Black-and-White Colobus (Colobus guereza) in the Kakamega Forest, Kenya
My study examined the costs and benefits of mixed-species associations of two primate species: blue monkeys (Cercopithecus mitis) and black-and-white colobus (Colobus guereza), also known as guerezas, in the Kakamega Forest, Kenya to understand the nature of the associations between primates with divergent feeding habits. I observed one group of blue monkeys and three groups of colobus whose home ranges overlapped with heterospecifics, collecting data on the frequency and duration of associations, as well as feeding, aggression and vigilance rates. I rejected the null hypothesis that associations are the result of chance by using a gas model (Hutchinson and Waser 2007) that predicts the expected number of associations that would occur by chance. I found that the association durations, however, were not longer than predicted by chance except for one guereza group, which supports a modified null hypothesis that groups are independently drawn to the same location where they meet. I examined potential predation avoidance and foraging benefits of associations. Neither species reduced individual vigilance rates, alarm call frequencies, nor intense alarm responses in associations, nor did they increase ingestion rates. Individuals occupied lower forest strata more often, and had a wider niche breadth in association, suggesting some foraging benefits, possibly resulting from improved predation detection when associated. The associations frequently occurred at forest edges and around human settlements which have exposed sodium-rich soil (important in both species’ diets), visible insects, and high-energy cultivated foods (occasionally eaten by blue monkeys). Both species may be receiving some predation avoidance benefits of having a larger group at vulnerable edge locations, but it appears that ultimately they are drawn to these sites, not each other, because they do not maintain their associations once initiated.
Mattila J, Heck KL Jr., Millstein E, Miller E, Gustafsson C, Williams S, Byron D (2008). Increased habitat structure may not always provide increased refuge from predation. Marine Ecology Progress Series. 361:15-20.