Physical properties of fruit and seeds ingested by primate seed predators with emphasis on sakis and bearded sakis.

Several primate radiations exhibit dental adaptations that enable them to gain access to seeds embedded in well-protected fruit. To a database drawn from published sources in which hardness of fruit and seeds were tested in the field, we added an additional 100+ species of plants used as resources by pitheciin primates (specifically, South American white-faced sakis (Pithecia pithecia) and bearded sakis (Chiropotes spp.). This sample allowed us to compare hardness of fruit and seeds and deduce the relative incisive and masticatory capability of several primate taxa (New World monkeys, Old World monkeys, prosimians and chimpanzees). Pitheciins have very well developed and highly modified anterior dentition that they use in gaining access to mechanically-protected fruit. In addition, their molars bear thin, but decussated enamel that protects the tooth enamel from crack proliferation. The ability of sakis (Chiropotes spp. and Pithecia pithecia) to open fruit orally was comparable to larger-bodied Old World seed predators-Lophocebus and Cercocebus. But, baboons and chimpanzees masticate seeds that are two to three orders of magnitude harder than sakis or mangabeys. In spite of their puncture abilities, ∼40% of foods ingested by pitheciins were in the range of a ripe fruit eater (Ateles paniscus). This raises the possibility that pitheciins exemplify Liem's paradox, that is, "that phenotypic specialization [is] not accompanied by ecological specialization" (Robinson and Wilson, 1998:224). Last, we examined the possibility that seeds may serve as fallback resources for primate seed predators. While pericarp hardness may vary seasonally for some seed predators (e.g., mangabeys), our data on bearded sakis and white-faced sakis suggest that seeds are their primary resources year round and pericarp hardness is unrelated to seasonal variation in rainfall. Pitheciins evolved specialized dentition that affords them access to relatively abundant and high-quality resources, a feeding strategy that results in minimal variation in resource availability seasonally.