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Mathias Franz


Speaker: Mathias Franz
Title: Winner and Loser Effects in Wild Baboons
Affiliation: Duke University
Date: Friday, December 5, 2014
Place and Time: Room 101, Love Building, 3:35-4:30 pm
Refreshments: Room 204, Love Building, 3:00 pm

Abstract. Many social animals form linear dominance hierarchies, which can influence access to limited resources and influence health and reproduction. Two primary, mutually inclusive hypotheses explain the proximate emergence of these hierarchies: (1) the `prior attributes hypothesis,' which posits that individual differences in fighting ability directly determine dominance ranks and (2) the `social dynamics hypothesis,' which posits that dominance ranks emerge from social self-organization dynamics, such as winner and loser effects (a well-described behavioral phenomenon in which winners tend to become more likely to win in subsequent encounters, and losers tend to become more likely to lose). While the first hypothesis is well supported, support for the second hypothesis is limited to experimental studies. Here, we present a novel statistical approach, based on the Elo rating method for cardinal rank assignment, that enables the detection of winner and loser effects in uncontrolled group settings. This approach identifies systematic variation in the statistical impact of winning and losing on future wins and losses, which facilitates tests of the prediction that winner and loser effects increase with aggression intensity. We used our approach to investigate long-term hierarchy dynamics in wild male baboons living in five social groups. Our results support the hypothesis that winner and loser effects influence male hierarchy dynamics in wild baboons. They indicate that the strength of winner and loser effects increases with increasing levels of male aggression. In addition, our results indicate the potential existence of a genetic basis for winner and loser effects that could be linked to other behavioral strategies, such as coalition formation. Finally, based on our findings, we identify the need for more empirical and theoretical work to examine whether agonistic behavioral strategies evolved to deal with temporal changes in individual fighting abilities.