How Social Context, Token Value, and Time Course Affect Token Exchange in Capuchin Monkeys (Cebus apella)

摘要

Although numerous studies have examined token-directed behaviors in primates, few have done so in a social context despite the fact that most primate species live in complex groups. Here, we provided capuchin monkeys with a relatively limited budget of tokens, likely to elicit intragroup competition, and, after an overnight delay, we allowed them to exchange tokens while in a group setting. We aimed to 1) evaluate whether social context affects token-directed behaviors of knowledgeable subjects, i.e., subjects already proficient in token exchange before the present study, as well as of na?ve subjects, i.e., subjects that never showed exchange behavior before this study; 2) appraise whether capuchins indeed value tokens; and 3) assess whether capuchins can refrain from throwing tokens outside their enclosure when the experimenter is not present. Overall, the social context positively affected high-ranking individuals and negatively affected low-ranking ones. All 6 high-ranking na?ve subjects, but none of the 4 low-ranking ones, quickly acquired token exchange behavior, whereas 9 of 12 low-ranking knowledgeable subjects, but only 1 high-ranking knowledgeable subject, never displayed token exchange in social contexts. Thus, competition constrained token exchange in low-ranking subjects and prompted exchange behavior in high-ranking na?ve subjects. Capuchins were unable to inhibit the exchange of valueless items when the experimenter was soliciting them and, at the group level, knowledgeable subjects did not exchange more valuable tokens than less valuable (or valueless) ones. However, the 3 high-ranking knowledgeable subjects that exchanged most of the tokens first preferentially exchanged more valuable tokens over less valuable or valueless ones. Finally, capuchins inhibited exchange behavior in the absence of the experimenter, thus recognizing the appropriate conditions in which a successful exchange could occur.