Group territory defense poses a collective action problem: individuals can free-ride, benefiting without paying the costs. Individual heterogeneity has been proposed to solve such problems, as individuals high in reproductive success, rank, fighting ability, or motivation may benefit from defending territories even if others free-ride. To test this hypothesis, we analyzed 30 years of data from chimpanzees (Pan troglodytes) in the Kasekela community, Gombe National Park, Tanzania (1978-2007). We examined the extent to which individual participation in patrols varied according to correlates of reproductive success (mating rate, rank, age), fighting ability (hunting), motivation (scores from personality ratings), costs of defecting (the number of adult males in the community), and gregariousness (sighting frequency). In contrast to expectations from collective action theory, males participated in patrols at consistently high rates (mean ± S.D. = 74.5 ± 11.1% of patrols, n=23 males). The best predictors of patrol participation were sighting frequency, age, and hunting participation. Current and former alpha males did not participate at a higher rate than males that never achieved alpha status. These findings suggest that the temptation to free-ride is low, and that a mutualistic mechanism such as group augmentation may better explain individual participation in group territorial behavior. 

Attached data files include summary data collected at Gombe National Park (1998-2007). For detailed methodology, please see the associated manuscript.

README File: README_MASSARO_2022_DATA_updated04mar2022.txt

R-code for data analysis: CodeforCorrelatesofBoundaryPatrols.R

Datasets: PPdata.xlsx, PatrolsandPeriph.xlsx, PP5yearPlots.xlsx, WholeStudyPatrolRate.xlsx

We do not provide access to the raw data used in some of these analyses, as this raw data represent a substantial fraction of the long-term data from Gombe, which are not publicly available at this time due to multiple ongoing studies, but are available from the corresponding author on reasonable request