Emily Miller

(M.A. Conservation Biology)

 

Mixed-Species Associations of Blue Monkeys (Cercopithecus mitis) and Black-and-White Colobus (Colobus guereza) in the Kakamega Forest, Kenya

 

 

Emily

Mixed-species associations are usually understood in terms of the costs and benefits that participant species experience.  These costs and benefits may be asymmetrical in direction and degree for the species involved.  The two major categories of proposed benefit are improved protection against predation and the improved acquisition of resources. 

 

Many researchers conclude that the predation avoidance benefit is the main driver of associations.   Foraging benefits may also explain why mixed-species associations occur more frequently than expected by chance.  Larger groups can monopolize food patches and exclude smaller groups.  Heterospecifics may enhance foraging efficiency if they have a greater knowledge of food availability and can act to guide their partner species to profitable feeding sites.  Heterospecifics may also be able to take advantage of foraging in different microhabitats when in association. 

 

Mixed-species associations can be costly for one or both species involved because of increased feeding competition as a result of increasing group size.  Mixed-species association may reduce the cost of intragroup feeding and mate competition relative to association in a larger single-species group.  Feeding competition is likely to be especially low when associations involve phylogenetically more distant taxa, such as colobines and cercopithecines, whose diets are more dissimilar than closely related species.  

 

Among primates, mixed-species associations are common among closely related (congeneric) species, whose ecological similarity in terms of resource use and predation threats likely contributes to their adaptiveness.   However, in Africa, associations between less closely related cercopithecines and colobines are also common. Phylogenetic difference has implications for why mixed-species associations occur: when very different taxa associate, dietary divergence is likely to influence both the costs and benefits of association.

 

To characterize the associations of one blue monkey group and three black-and-white colobus groups in Kakamega Forest, I am using population density data to first look at whether their associations occur more frequently than predicted by chance.  I am examining the potential benefits and costs of these mixed-species associations using data I collected on vigilance rates, ingestion rates, diet composition, alarm calls and responses, travel distance and speed, microhabitat usage, agonism, and association initiation and termination patterns.  For each species, I am comparing these measures for when the species was in and out of association to better understand the occurrence of associations between two phylogenetically distant primate taxa.

 

Publication:

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.