Dietary response of chimpanzees and cercopithecines to seasonal variation in fruit abundance. I. Antifeedants

In order to understand dietary differentiation among frugivorous primates w ith simple stomachs, we present the first comparison of plant diets between chimpanzees and cercopithecine monkeys that controls for food abundance. O ur aim was to test the hypothesis that monkeys have a more diverse diet as a result of their dietary tolerance for chemical antifeedants. Our study sp ecies are chimpanzees, blue monkeys, redtail monkeys, and gray-cheeked mang abeys living in overlapping ranges in Kibale National Park, Uganda. We inde xed food abundance by the percentage of trees having ripe fruit within the range of each,group; it varied widely during the year. Chimpanzees spent al most 3 times as much of their feeding time eating ripe fruits as the monkey s did and confined their diets almost exclusively to ripe fruits when they were abundant. Monkeys maintained a diverse diet at all times. When ripe fr uit was scarce chimpanzee and monkey diets diverged Chimpanzees relied on p iths as their main fallback food whereas monkeys turned to unripe fruits an d seeds. For each primate group we calculated the total weighted mean intak e of 5 antifeedants condensed tannins (CT), total tannins assayed by radial diffusion (RD), monoterpenoids (MT), triterpenoids (TT), and neutral-deter gent fiber (NDF). Monkeys had absolutely higher intakes of CT, RD, MT, and TT than those of chimpanzees, and their intake of NDF did not differ from t hat of chimpanzees, appearing relatively high given their lower body weight s. However contrary to expectation, dietary divergence during fruit scarcit y was not associated with any change in absolute or relative intake of anti feedants, For example, fi-nit scarcity did not affect the relative intake o f antifeedants by cercopithecines compared to chimpanzees. Our results esta blish chimpanzees as ripe-fruit specialists, whereas cercopithecines are ge neralists with a higher intake of antifeedants. The low representation of r ipe;re fruits in the diets of cercopithecines has nor been explained An imp ortant next step is to test the hypothesis that the difference between Kiba le chimpanzees and cercopithecines represents a more general difference bet ween apes and monkeys.