Consequences of changing numerical asymmetries on intergroup relations among tufted capuchins: a case study

TUJAGUE, MARÍA PAULA ; SCARRY, CLARA JOAN

Minneapolis

Congreso; 80th Annual Meeting of the American Association of Physical Anthropologists; 2011

American Association of Physical Anthropologists

Game theory suggests that escalation of aggression is unprofitable when competitors are able to accurately assess one another due to strong asymmetries in competitive ability or through prior interactions. Thus, changes in the resource holding potential (RHP) of one competitor may alter both the nature of interactions and each competitor?s access to resources. We followed two groups of tufted capuchin monkeys (Cebus apella nigritus) in Iguazú National Park, Argentina, with intermittent contact between June 2008 and August 2010. During this period, the larger group experienced a change in the male dominance hierarchy, resulting in the death or dispersal of all adult males and the ascendance of a subadult male to the dominant position. This reduced the numerical advantage in the number of males between the two groups, although the ratio of total group sizes remained constant (2:1). Following this shift, the degree of escalation during intergroup encounters increased, including reversals in the dominance relationship of the groups. These changes were associated with changes in the use of overlapping areas. In the six months following the takeover, the area of home range overlap doubled, and the formerly dominant group?s area of exclusive access was reduced by half due to more frequent and longer incursions by neighboring groups. These observations suggest that RHP in tufted capuchins is related to either male group size or the competitive ability of the dominant male and that reduced competitive ability may increase both direct costs of intergroup aggression and costs of between-group scramble competition.