Defining Higher Levels in the Multilevel Societies of Geladas (Theropithecus gelada)

Abstract

Multilevel societies, identified by two or more nested levels (or modules) of organization, have been touted as some of the most complex social systems. However, few empirical studies have effectively quantified the association patterns that delineate the various levels in such societies. In particular, the multiple levels of gelada society were first described >3 decades ago, yet no operational definitions exist for the higher levels, i.e., levels above the one-male unit. In geladas, multiple units form aggregations that fission and fuse throughout the day, and throughout the year, blurring the distinctions between previously described higher social levels: teams, bands, and communities. Here we use 5 yr of data on the daily composition of a population of geladas living in the Simien Mountains National Park, Ethiopia to test the hypothesis that higher levels of gelada organization are discrete entities. If gelada aggregations are nothing more than a group of units that share a home range, then we expect a continuous distribution of unit association. If, however, gelada aggregations are indeed discrete organizational levels, then we expect discontinuity in the patterns of association. We found significant discontinuity at the 50% association level, indicating a sharp distinction between members of the same band (>50% association) and members of the same community (<50% association). We also found evidence that recently fissioned units form teams that associate significantly more than other band members. Thus, despite their extremely fluid social organization, gelada social levels are nevertheless clearly identifiable and quantifiable. Based on these results, we suggest that gelada society is an extremely flexible, multilevel society with fission–fusion dynamics, and as such gelada society presents an unusual example for understanding the evolution of modular societies.

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Acknowledgments

We thank the Ethiopian Wildlife Conservation Authority and the wardens and staff of the Simien Mountains National Park for granting us permission to conduct this research. We thank the guest editors for inviting us to participate in this special issue on multilevel societies. We also thank two anonymous reviewers for their comments on previous versions of this manuscript. We are extremely grateful to H. Gelaye, E. Jajaw, A. Fanta, A. Le Roux, C. Wilton, E. Roberts, D. Pappano, and J. Jarvey for their help with data collection in the field. Funding was provided by the Wildlife Conservation Society (SSF grant 67250), the National Geographic Society (grant 8100–06), the Leakey Foundation, the National Science Foundation (grants BCS-0715179, BCS-0962118, Graduate Research Fellowship Program), the University of Pennsylvania, and the University of Michigan. This research was approved by the University Committee on Use and Care of Animals (UCUCA) at the University of Michigan and adhered to the laws and guidelines of Ethiopia.

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Correspondence to Noah Snyder-Mackler.

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Snyder-Mackler, N., Beehner, J.C. & Bergman, T.J. Defining Higher Levels in the Multilevel Societies of Geladas (Theropithecus gelada). Int J Primatol 33, 1054–1068 (2012). https://doi.org/10.1007/s10764-012-9584-5

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Keywords

  • Band
  • Community
  • Modular society
  • One-male unit
  • Social organization
  • Team
  • Theropithecus