No abstract

This study aimed to assess the conditions under which monkeys might produce common effects in an instrumental task. One group of Tonkean macaques (Macaca tonkeana) and two groups of rhesus macaques (M. mulatta) were given series of tests in which food incentives were placed under stones of various weights. In the Tonkean group, the simultaneous action of two subjects in moving the same stone was a relatively frequently occurring event: coaction was more effective than individual action for moving heavy stones; however, there were no signs of coordination among partners and no improvement through learning. In rhesus groups, instances of coaction were extremely rare, and rates of agonistic interactions were higher than in the Tonkean group. It is suggested that “coproduction” represented an emergent phenomenon resulting from social interactions and, as such, was dependent on the level of interindividual tolerance.

The clumped distribution of food resources promotes food defensibility and can lead to the monopolizing of resources by high-ranking individuals. However, the balance of power is set at different levels according to societies, meaning that resource partitioning should vary between them. This study investigates whether dominance asymmetry and resource partitioning are related in non-human primates by comparing two species with contrasting social styles, namely rhesus macaques (Macaca mulatta) which display strong social intolerance and a steep gradient of dominance, and Tonkean macaques (Macaca tonkeana), which exhibit higher levels of tolerance and more balanced dominance relationships. Study groups were kept in semi-free ranging conditions. Animals were provided with fruit in three different clumped conditions during 30-min trials. We found that higher-ranking rhesus macaques had priority for the access to fruit: these individuals spent longer in the feeding area in the first 10-min period of trials, while lower-ranking individuals had diminished access to fruit under the most clumped condition; this was associated with sustained agonistic interactions. Dominance effects were weaker in Tonkean macaques. They exhibited co-feeding between high- and low-ranking individuals in the first period; there was no significant effect of dominance even in the most clumped condition; and frequencies of agonistic interactions remained moderate relative to the number of individuals present in the feeding area. These results show that food resources were more equitably distributed among group members in tolerant macaques than in their intolerant counterparts. Dominance gradient and social tolerance may be considered as two aspects of the same phenomenon.