, Volume 57, Issue 1, pp 17–28 | Cite as

Group structure predicts variation in proximity relationships between male–female and male–infant pairs of mountain gorillas (Gorilla beringei beringei)

  • S. RosenbaumEmail author
  • A. A. Maldonado-Chaparro
  • T. S. Stoinski
Special Feature: Original Article Understanding the Variability of Gorilla Social Structure


Relationships between conspecifics are influenced by both ecological factors and the social organization they live in. Systematic variation of both—consistent with predictions derived from socioecology models—is well documented, but there is considerable variation within species and populations that is poorly understood. The mountain gorilla (Gorilla beringei) is unusual because, despite possessing morphology associated with male contest competition (e.g., extreme sexual dimorphism), they are regularly observed in both single-male and multimale groups. Both male–female and male–infant bonds are strong because males provide protection against infanticide and/or predation. Risk of these threats varies with social structure, which may influence the strength of social relationships among group members (including females and offspring, if females with lower infant mortality risk are less protective of infants). Here, we investigate the relationship between group structure and the strength of proximity relationships between males and females, males and infants, and females and offspring. Data come from 10 social groups containing 1–7 adult males, monitored by the Dian Fossey Gorilla Fund’s Karisoke Research Center in Volcanoes National Park, Rwanda. After controlling for group size and infant age, association strength was similar for male–female pairs across group types with both dominant and nondominant males, but male–infant relationships were strongest in single-male groups where paternity certainty was high and animals had fewer social partners to choose from. The male:female and male:infant ratios better predicted both male–female and male–infant associations than the absolute number of males, females, or infants did. The fewer the number of males per female or infant, the more both pair types associated. Dominant males in groups containing fewer males had higher eigenvector centrality (a measure of importance in a social network) than dominant males in groups with more males. Results indicate that nondominant males are an important influence on relationships between dominant males and females/infants despite their peripheral social positions, and that relationships between males and infants must be considered an important foundation of gorilla social structure.


Social plasticity Group structure Network centrality Variable group composition Association strength Multimale groups 



The authors wish to thank M. Robbins, J. Silk, an anonymous reviewer, and members of the Lincoln Park Zoo’s Lester E. Fisher Center and Davee Center for their helpful comments on the data and manuscript. The Karisoke Research Center is a project of the Dian Fossey Gorilla Fund International (DFGFI). The authors and DFGFI thank the Rwandan government and national park authorities for their long-term commitment to gorilla conservation and their support of the Karisoke Research Center. DFGFI is greatly indebted to the many Karisoke field assistants and researchers for their work collecting demographic and behavioral data over the last 48 years. We wish to acknowledge the many staff members who have shown extraordinary commitment under dangerous conditions, in some cases giving their lives while protecting and studying the gorillas. This work was funded by the Wenner-Gren Foundation, the LSB Leakey Foundation, the National Science Foundation (doctoral dissertation improvement grant #1122321), and the donors who support DFGFI.

Compliance with ethical standards

Conflict of interest and statement on the welfare of animals

The authors declare that they have no conflict of interest. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.


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Copyright information

© Japan Monkey Centre and Springer Japan 2015

Authors and Affiliations

  1. 1.Department of AnthropologyUniversity of California—Los AngelesLos AngelesUSA
  2. 2.Department of Ecology and Evolutionary BiologyUniversity of California—Los AngelesLos AngelesUSA
  3. 3.The Dian Fossey Gorilla Fund InternationalAtlantaUSA
  4. 4.Institute for Mind and BiologyUniversity of ChicagoChicagoUSA

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