Foraging networks and social tolerance in a cooperatively breeding primate (Callithrix jacchus)

Within-group competition over food resources can be a major cost of social
living. In the wild, foragers are confronted with social (e.g.
hierarchical rank) and ecological (e.g. food availability and
distribution) challenges that affect their foraging decisions and feeding
success. Exhibiting prosocial behaviors, such as tolerance at feeding
sites, can benefit group members by developing affiliative social
relationships, enhancing access to resources and maximizing fitness. We
examined social tolerance at feeding sites in Callithrix jacchus, a
cooperatively breeding primate species. We investigated the set of social
(rank, age, sex) and ecological (food availability) factors that influence
the structure and dynamics of within-group foraging association networks.
We designed and conducted an experimental field study of four wild groups
of common marmosets in which we controlled food distribution (concentrated
or scattered) and productivity (high, medium, or low food rewards). Then,
we used social network analyses to assess the number and strength of
foraging associations among group members, their effects on individual
food consumption, and whether recent experiences with conspecifics during
foraging affected subsequent associations. Overall, common marmoset
foraging association networks were cohesive, as group members jointly
occupied feeding sites. The number and strength of associations varied
depending on the ecological context. Associations were stronger during
conditions in which food was concentrated at a single site. Individuals
obtained greater access to food resources when sharing a feeding site with
conspecifics, but once a food item was obtained, the forager moved to a
nearby tree and consumed it away from others. Additionally, the strength
of previous foraging associations and subsequent levels of social
tolerance at feeding sites were positively related, a relationship
compatible with the ability of memorizing associations over time and
recalling the information in future decision-making. In sum, marmosets
adjusted their partner choices and the strength of foraging associations
in response to food availability. They exhibited increased social
tolerance at feeding sites during conditions in which opportunities for
contest competition were expected to be greatest. These cooperative
breeding primates appear to mutually benefit by maintaining cohesive and
strong affiliative relationships, and by increasing opportunities for
coordinated behavior and offspring survival.