Reevaluation of dominance hierarchy in bonobos (Pan paniscus)

Abstract

While dominance relationships have been widely studied in chimpanzees, in bonobos, dominance style and linearity of hierarchy are still under debate. In fact, some authors stated that bonobo hierarchy is nonlinear/ill-defined, while others claimed that it is fairly linear. In this paper, we test the hypothesis that a shift in group composition determines changes in linearity of hierarchy. To test this hypothesis, we collected data on one of the largest captive groups in the world, in the Apenheul Primate Park (The Netherlands). We investigated the linearity of the hierarchy in two different periods, with a shifting group composition. We used the corrected Landau's index and David's scores to estimate which animals were most dominant. The major overall result of our study is that hierarchy is fairly nonlinear in this group: during the first study period (eight adults), the hierarchy was nonlinear, whereas during the second one (six adults), it failed to reach statistical linearity. We argue that the reduction of the number of adults is the principal factor affecting linearity. We also found that dominance interactions were evenly distributed across sex classes in both study periods. Furthermore, no correlation was observed between age/body weight and rank. As for the overall dominance relationship between males and females, our results suggest that there is no exclusive female dominance in the Apenheul group. The dominance style of bonobos may be loose and differentially expressed in diverse groups or in the same group, along with shifting conditions.

Dominance style of female white‐faced capuchins

“…Finally, reconciliation and consolation are common (de Waal and Aureli, 1996), indicating that they exhibit a relaxed dominance style. Studies of dominance in bonobos (Pan paniscus) have produced conflicting results but generally classify dominance style as relaxed; direct measures associated with dominance style include hierarchical linearity (nonlinear), formal submission (not present), and conciliatory tendencies (high at 50-60%) (Vervaecke et al, 2000;Palagi et al, 2004;Paoli et al, 2006).…”

Of lion manes and human beards: some unusual effects of the interaction between aggression and sociality

“…Humans do certainly have both dominance hierarchies and submissive behaviors, but these appear to vary widely across cultures and their existence and extent in precultural humans is difficult to estimate. While there appears to be a linear dominance hierarchy in male chimpanzees (Goldberg and Wrangham, 1997), this appears not to be so in bonobos (Paoli et al, 2006); these having equal claim to the ancestral line from which humans split. Perhaps lions and humans came to their need for protection against lethal intraspecific attack through slightly different routes; Lions with long-term lethal weapons but lately evolving a social life-style, whereas people are from a line with substantial, though not clearly delineated, sociality, but lately evolving the development and use of lethal weapons.…”

Considering the role of social dynamics and positional behavior in gestural communication research

“…Finally, bonobos exhibit flexibility in group size and composition, as well as diversity in their social relationships. A dramatic difference between chimpanzee and bonobo social behavior is that females are often dominant to males in bonobo society, though dominance hierarchies are not always straightforward [Paoli et al, 2006;White & Wood, 2007]. Females even form coalitions with each other in agonistic encounters against males or when defending food sources against males [Kano, 1992;Parish, 1994], and interact with each other regularly via sexual behavior [Hohmann & Fruth, 2000;Hohmann et al, 1999].…”