Study Finds That Female Chimpanzees Contribute Greatly to Territory Protection

A study has found that female chimpanzees play a crucial part in their group's territory protection and expansion. An international research team has conducted an extensive survey of several neighboring western chimpanzee groups, and they found that not only females but the whole group play essential roles in intergroup competition.

This contradicts previous beliefs among scientists. The Max Planck Institute for Evolutionary Anthropology researchers showed that the maintenance of territory and competition among neighboring groups is the responsibility of the whole group. The study focused on chimpanzee populations in the UNESCO World Heritage Center, Taï National Park.

Previous studies have highlighted the role that adult males play in maintaining territory, probably due to an anthropocentric bias. Chimpanzees are among humans' closest extant relatives. Male chimpanzees are actively engaged in intergroup conflict and concerns regarding territory. Females usually do not engage in this role, at least in some eastern chimpanzee groups.

Previous studies on western chimpanzees in Taï National Park located at Côte d'Ivoire have already shown how females could be playing a more significant part in territory behavior, something scientists have not considered before. Therefore, due to these newer findings, some questions came up regarding the competitive ability of chimpanzees in territorial contests, because of this variation in their social systems.

First, author Sylvain Lemoine said that in order to shed light on the mechanisms of dominance and group competition in social species such as these, long term research data from many groups in a population are needed. The new study they published explored such mechanisms in the groups of western chimpanzees.

They gathered over 20 years of observational data from four western chimpanzee neighboring communities for the TCP or Taï Chimpanzee Project. Data collected include intergroup encounters and ranging patterns. The study revealed that group size is a more critical factor than the adult male population in cost and benefit variations as well as intergroup competition.

Larger groups that comprise females, juveniles, and adolescents have the advantage over the smaller groups by having larger territories and getting less pressure from neighboring groups. This translates into safer and larger feeding areas, which then brings more individual reproductive advantages.

According to TCP director and co-senior author Roman Wittig, 'bisexually-bonded' mating groups of a community occupy similar territory instead of becoming segregated in a smaller territorial range. Both males and females perform maintenance of their area through the conduct of border patrolling and engagement in conflicts against hostile groups. Their socializing and grouping patterns could explain how larger group size, instead of just how many males, provide competitiveness.

According to Lemoine, their study's findings could account for the low number of killings between communities in comparison to populations of eastern chimpanzees. This is due to the fact that when group conflicts arise and all community members are engaged in a contest, there is a lesser chance of having an imbalance in power as well as a smaller chance to kill one's neighbor.

Co-senior author Catherine Crockford concludes by saying that there is now mounting evidence supporting the view that cooperation between individuals and between the sexes has undergone selection from the intergroup competition. This has substantial implications in the evolution of social species cooperation, particularly among humans. There is a need for a more long term and continuous research to understand the relationship between cooperation and competition in chimpanzees, and as it relates to human evolution.