Female gorillas form highly stable dominance relationships

Area of Science:

• Primate Social Behavior
• Animal Ecology
• Evolutionary Biology

Background:

• Dominance hierarchies are common in animals, influencing resource access and fitness.
• Hierarchy stability often depends on factors like age, immigration, or kinship, rather than just physical strength.
• Female gorillas typically disperse from their groups, disrupting social bonds and alliances, leading to predictions of unstable dominance.

Purpose of the Study:

• To investigate the stability of dominance relationships among female gorillas.
• To test the hypothesis that dispersal leads to unstable social hierarchies in female gorillas.
• To explore the evolutionary roots of dominance dynamics in hominids.

Main Methods:

• Analysis of a 24-year dataset spanning five groups of both gorilla species (Gorilla gorilla and Gorilla beringei).
• Examination of dyadic relationships and rank changes over extended periods of female co-residence.
• Quantification of rank reversals and passive mobility (rank changes due to emigration or death of others).

Main Results:

• Female gorillas form remarkably stable dominance relationships, maintained throughout their group tenure (average co-residence of 4.8 years, up to 17.3 years).
• Rank reversals were rare, observed in only two out of 92 female dyads.
• Most rank improvements occurred passively through the departure or death of higher-ranking individuals.

Conclusions:

• The study challenges the presumed link between dispersal and hierarchy instability in female gorillas.
• Findings suggest that stable dominance hierarchies can be maintained despite female dispersal, potentially due to high costs of challenging dominant individuals.
• The stability observed in female gorilla dominance mirrors that in chimpanzees, indicating deep evolutionary roots in hominid social structures.