The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)

Relationship of dominance ranks to age and coalition formation among male chimpanzees at Ngogo


Anthropology, Yale University

April 14, 2016 8:45, A 706/707 Add to calendar

Male chimpanzees (Pan troglodytes) compete for status and form dominance hierarchies. Attaining high rank leads to reproductive payoffs. Males also form alliances with which they can improve and maintain their ranks, and alliance formation can influence mating opportunities. I used data on the unusually large Ngogo chimpanzee community, collected between 1995 and 2015, to investigate how ranks vary with age and with variation in coalition networks. Data on decided agonistic interactions, analyzed with MATMAN, yielded linear hierarchies for each year. The relationship of rank to age followed an inverse U-shaped trajectory described by a polynomial regression with age and age2 as predictors (F = 201.52, r2 = 0.41, p < 0.001). Males attained their maximum ranks, which varied considerably, at a mean age of 32y, long after growth completion.

I used data on coalitions to calculate four measures of coalition network centrality and power with UCINET (Bonacich power; eigenvector centrality; degree centrality; node betweenness). I used these plus age, age2, and male identity as predictors in a mixed-effects GLM examining variation in male ranks. A model including Bonacich power, age, and age2 (all with significant effects) provided the best fit (Wald χ2 = 980.09, p < 0.001) and performed significantly better than one including only the age variables. Overall, results show that males at Ngogo queue for ranks and that participation in coalitions influences male status.

L.S.B. Leakey Foundation, National Geographic Society, US National Science Foundation BCS-0215622 and IOB-0516644, Yale University