Foraging, food choice, and food processing by ripe-fruit specialists
Studies of interspecific competition and niche separation have formed some of the seminal works of ecology. An 18 month study was conducted, comparing the feeding ecologies of two sympatric, closely-related ripe-fruit specialists.
In this study Humboldt's woolly monkeys (Lagothrix lagotricha poeppigii) were compared with white-bellied spider monkeys (Ateles belzebuth belzebuth) in Amazonian Ecuador. Woolly monkeys in the terra firme forest live at roughly triple the density of spider monkeys (31 versus 11.5 animals per square km). Woolly monkeys spend 17% of their time foraging, while spider monkeys spend only 1% of their time foraging. Spider monkeys alone fed on soil and termitaria, which are rich in phosphorus. Woolly monkeys are not hard-fruit specialists. Their fruit diet is significantly more diverse than that of spider monkeys. Dietary overlap between the two species is high, yet each specializes to some degree on a different set of fruit resources. Woolly monkeys visit more food sources per unit of time, feed lower in the canopy, visit more small food patches, and prey on more seeds. Spider monkeys feed on fewer, richer food sources and are more than twice as likely to return to a particular fruit source than woolly monkeys are. Spider monkeys maximize fruit pulp intake, carrying more intact seeds in their guts, while woolly monkeys minimize seed bulk swallowed through more careful food processing. Surprisingly, several preferred spider monkey foods with high fat content and large seeds are avoided by woolly monkeys. The different ecological dimensions involved in niche separation between the two species is outlined and the possible impetus for their evolutionary divergence is discussed.
Title: Foraging, Food Choice, and Food Processing by Sympatric Ripe-Fruit Specialists: Lagothrix lagotricha poeppigii and Ateles belzebuth belzebuth
Author: J. Lawrence Dew