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Updated: Feb 13, 2026

Linking Predation Risk, Herbivore Physiological Stress and Microbial Decomposition of Plant Litter
Published on: March 12, 2013
Trade-off between fertility and predation risk drives a geometric sequence in the pattern of group sizes in baboons
R I M Dunbar1,2, Padraig MacCarron3, Cole Robertson3
1Department of Experimental Psychology, University of Oxford, South Parks, Oxford OX1 3UD, UK robin.dunbar@psy.ox.ac.uk.
Abstract:
Group-living offers both benefits (protection against predators, access to resources) and costs (increased ecological competition, the impact of group size on fertility). Here, we use cluster analysis to detect natural patternings in a comprehensive sample of baboon groups, and identify a geometric sequence with peaks at approximately 20, 40, 80 and 160. We suggest (i) that these form a set of demographic oscillators that set habitat-specific limits to group size and (ii) that the oscillator arises from a trade-off between female fertility and predation risk.
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