Resumen
- Social structures emerge in primate groups mainly as a response to environmental pressures. Social structure impacts significantly on predator detection, food gathering and reproduction, and it is also an indicator of social condition and age and sex categories within the group. Differentiated activities which depend on social status, sex and age have been described in established social groups of primates. Dominance patterns influence the behavior of some species. It seems that the night-time spatial arrangement of members of a primate group is an anti-predation strategy, either by increasing detection and defensive capabilities in the case of large sleeping groups, or by emphasizing inconspicuousness in the case of more solitary sleepers. The persistence of social organization during rest-activity cycles in primate groups allows for the prediction that individuals in a group having the same monitoring needs may alternate their rest-activity condition to assure vigilance. In this study, we examined the rest and activity conditions of two peripheral individuals in an established social group of M. arctoides. Each subject was videorecorded twice for two continous periods of 24 hours each, totaling a videorecording of 96 hours. The rest and activity conditions observed in both subjects were grouped in the four possible conditions: Condition 1. Subject A resting, subject B resting; Condition 2. Subject A resting, subject B active; Condition 3. Subject A active, subject B resting; Condition 4. Subject A active, subject B active. These were compared with a concordance test. Results revealed that peripheral males alternated their rest-activity cycles. That is, while one subject was resting, the other remained active. The possibility that rest-activity alternation is an adaptation to maintain constant vigilance is discussed.