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Self-organised dominance relationships: A model and data of primates

Self-organised dominance relationships: A model and data of primates
Jan Wantia


Department of Biological Sciences, University of Groningen, 9700 AB Groningen, THE NETHERLANDS.


Part I of this thesis deals with female dominance, where it occurs, and how the degree of female dominance may be influenced. In part II, the relation of social organisation within groups (different compositions of personality types, dominance style) and the success of group in competition between groups is investigated. In the following, the new findings are summarised and discussed more generally. As well, critique points of the models that have been raised frequently are addressed, and finally a short outlook regarding future work and extensions of the models is given.

Although some or all females may dominate males in several primate species, female dominance as a phenomenon in social organisations has not been studied systematically (except for a few lemur species). However, in analysing empirical data on female dominance in primates for the first time, it turns out that it occurs in many different species to various degrees (Chapter 2). Model results suggest that influences on the degree of female dominance are manifold. In Chapter 3, a number of unexpected causes are presented, such as food distribution, sexual attraction, and group cohesion: All of these affect which and how often individuals meet, which in turn influences the development of the hierarchy via winner-loser effects. Chapter 4, in turn, focuses on the consequences of winner-loser effects and inter- versus intra-sexual interactions. It appears that the degree of female dominance may be influenced not only directly by inter-sexual interactions, but also indirectly via the proportion of males in the group. In addition, from the model a new method emerged for estimating what role inter-sexual fights, and hence, winner-loser effects, play in the development of intra- sexual hierarchies in real primates. When applied to eight species of the genus Macaca, it appears that self-reinforcing winner-loser effects are effective in inter-sexual encounters, but not as much as those in intra-sexual fights.

The finding that the degree of female dominance relates to the proportion of males in a group inspired an analysis of female dominance in empirical data of 22 primate species (chapter 5). Here a positive correlation between female dominance and the proportion of males is confirmed. Surprisingly, this correlation is independent of the degree of sexual dimorphism.

In sum, the findings presented in Part I suggest that the degree of female dominance is not an entirely species-specific trait. This is supported by empirical data, which document large variation in the degree of female dominance even between different groups of the same species (see chapter 2). Rather, the interactions among individuals also influence the degree of female dominance.