RESUMEN
Shifting to fallback food (FBF) consumption and crop raiding are behavioral adjustments that support primates' ability to endure in human-altered habitats. Nutritional models predict that the consumption of preferred foods leads to increased competition, while consumption of staple fallback foods results in decreased competition. We analyzed the competitive regime faced by individuals in a group of 133 blond capuchin monkeys (Sapajus flavius), an endangered species that inhabits a 270-ha fragment of Atlantic forest in northeast Brazil. During the study year, quantitative analyses show that fruits were a preferred food, while sugarcane was used as a staple FBF. As predicted by primate fallback foraging models, the consumption of sugarcane helped the group to survive in this fragment by providing these animals with half of the food they consumed throughout the year. Contrary to predictions, group dispersion increased with greater fruit abundance, while direct competition peaked during the consumption of sugarcane. We suggest that, although it is abundant and scattered in the area, the long handling time required to process sugarcane before consumption facilitates the direct competition. Overall, the pattern found indicates that consumption of a staple FBF does not directly translate into decreased competition and increased stability of social groups in forest fragments.