Inter-group relationships influence territorial defence in mountain gorillas

Area of Science:

• Primate behavior
• Socio-ecology
• Animal behavior

Background:

• Territoriality is common in species, with human space tolerance influenced by social bonds.
• The role of inter-group social relationships in non-human spatial use is poorly understood.
• Long-term relationships may evolve through shared resource access and dispute resolution.

Purpose of the Study:

• Investigate how social relationships influence spatial use and inter-group encounters in mountain gorillas.
• Examine the impact of social and spatial contexts on aggression and affiliation during encounters.
• Understand the role of retained social bonds in post-dispersal relationships.

Main Methods:

• Analyzed 16 years of simultaneous movement and interaction data from 17 mountain gorilla groups.
• Quantified aggressive and affiliative behaviors during inter-group encounters.
• Assessed the influence of social history and spatial location (core vs. peripheral home range) on interactions.

Main Results:

• Observed territorial defense, with increased aggression towards home range centers.
• Groups that previously split exhibited more affiliation and less aggression in peripheral areas.
• Core home range encounters consistently resulted in higher aggression, irrespective of group history.

Conclusions:

• Social relationships between mountain gorilla groups persist after fission.
• These relationships facilitate reduced aggression when accessing neighbors' peripheral home ranges.
• Reduced inter-group aggression in shared spaces may drive the evolution of long-term relationships and complex societies.