One of the most important constraints on primate population growth is thought to be access to food resources, but demonstrating this connection has been challenging. This project began efforts to test whether between-species feeding competition is responsible for the spatial gradient in blue monkey (Cercopithecus mitis) population density within Kibale National Park, Uganda. We studied groups of blue monkeys and their main competitors (redtail monkeys, Cercopithecus ascanius, and greycheeked mangabeys, Lophocebus albigena).
Preliminary data indicated that the blue monkey groups reduce feeding competition with other species by being positioned at the leading edge of the mixed-species group; this allows them to reach fruit trees before other species arrive and to consume the highest-quality fruits. We have also observed interesting, preliminary differences in how the blue groups interact with redtails and mangabeys. The BN1 group, located on the eastern side of the Ngogo trail system, has few direct interactions with redtails and mangabeys though they are in frequent spatial proximity, while the BN2 group, located in the central part of the trail system, appears to be much more aggressive toward other species. The BN1 group is also very socially fluid, a characteristic not previously observed in this species, compared to the more normal and cohesive BN2 group.
This study also revealed that the current size of each blue monkey group at Ngogo is far smaller than what was recorded during the last study of this sub-population, which occurred in 2009. During the earlier study, groups contained an average of 10 adult females whereas they currently contain an average of just 3 females. A reduction in group size may be the result of group fissions (normally precipitated by resource limitation) or mortality (possibly due to predation by chimpanzees, or by starvation). Also in contrast to the earlier study, the current blue monkey groups appear to spend less time alone – so little, in fact, that it may be challenging to compare study parameters when alone versus when in association.
Finally, this project provided a field-based training opportunity for an undergraduate student racially underrepresented within STEM fields, in order to strengthen her prospects for admission to a top graduate program in behavioral ecology and conservation. ($8,100)