Cheek pouch use in relation to interspecific competition and predator risk for three guenon monkeys (Cercopithecus spp.)

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Abstract
Forest guenons (Cercopithecus spp.) are often found in polyspecific associations that may decrease predator risk while increasing interspecific competition for food. Cheek pouch use may mitigate interspecific competition and predator risk by reducing the time spent in areas of high competition/predator risk. I investigated these ideas in three forest guenons: Campbell’s monkey (Cercopithecus campbelli), spot-nosed monkey (C. petaurista), and Diana monkey (C. diana). I present 13 months of scan sample data from Taï Forest, Côte d’Ivoire, including 3,675, 3,330, and 5,689 records of cheek pouch distention, to quantify cheek pouch use, for Campbell’s, spot-nosed, and Diana monkeys, respectively. Cheek pouches are often used to hold fruit, so I first predicted that the most frugivorous species, Diana monkeys, would have the most cheek pouch distension. Spot-nosed monkeys ate the least amount of fruit over the study period and had the least distended cheek pouches, suggesting the importance of frugivory in relation to cheek pouch distension for this species. This was not a sufficient explanation for Campbell’s monkeys; Campbell’s ate fruit less than Diana monkeys, but had more distended cheek pouches, suggesting that cheek pouch use was not simply a reflection of high frugivory. From the interspecific competition hypothesis, I predicted that Campbell’s monkeys would have more distended cheek pouches than Diana and spot-nosed monkeys, and more distended cheek pouches when associated with Diana because Campbell’s monkeys have the highest potential for interspecific competition with dominant Diana monkeys. From the predator risk hypothesis, I predicted that Campbell’s would have more distended cheek pouches when not associated with highly vigilant Diana monkeys. Campbell’s monkeys had the most distended cheek pouches overall, but had more distended cheek pouches when not in association with Diana, suggesting the greater importance of predator risk rather than interspecific competition in Campbell’s cheek pouch use.