The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Group size, age, and reproductive state affect dominance in wild female Hanuman langurs (Semnopithecus entellus schistaceus)


1Department of Anthropology, Stony Brook University, 2Department of Anthropology, University of Illinois

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Female dominance hierarchies are assumed to be the consequence of the competitive regime with a nepotistic structure reflecting within-group contest competition for food. Hanuman langurs seem to be an exception with despotic, age-inversed hierarches and individualistic, unstable ranks reported for a provisioned population with high levels of contest competition. It has also been assumed but not yet shown that females fall in rank after parturition. Here, we examine female dominance relationships and hierarchies through time in wild, unprovisioned Hanuman langurs at Ramnagar (Nepal); a population known to experience within-group contest competition. We observed one medium sized group (MG) and one large group (LG) averaging 6.9 and 13.6 adult females, respectively, for 5 years each between 1991 and 1997. Based on 12,490 dyadic displacement interactions, stable periods were identified (N=14 for MG, N=31 for LG) and dominance hierarchies constructed with the program MatMan. In both groups, dominance relationships had high directional consistency (DCI>0.95) and hierarchies were significantly linear (P<0.05). Rank was significantly negatively related with age, while the presence of maternal kin had no effect. Reproductive status affected dominance rank with females occupying lower ranks before conception and after birth. Ranks were overall unstable with the number of adult and juvenile females both contributing to this effect (multiple regression, P<0.05). These results match earlier findings for a provisioned population. In female Hanuman langurs, competition seems to be most intense around conception, creating rank instability, which is further exacerbated by the number of adult as well as maturing females in the group.

Data collection supported by the Alexander von Humboldt Foundation, the Ernst Stewener Foundation, the German Academic Exchange Service, and the German Research Council.

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