Cheating monkeys undermine group strength in enemy territory

Margaret Chatham Crofoot, Ian C. Gilby

Research output: Contribution to journalArticle

43 Scopus citations

Abstract

Inmany social animals, group-mates cooperate to defend their range against intrusion by neighboring groups. Because group size tends to be highly variable, such conflicts are often asymmetric. Although numerical superiority is assumed to provide a competitive advantage, small groups can generally defend their ranges, even when greatly outnumbered. The prevailing explanation for this puzzling phenomenon is that individuals in relatively large groups experience a greater temptation to flee from conflicts, in effect leveling the balance of power. Using playback experiments simulating territorial intrusions by wild capuchin monkey (Cebus capucinus) groups, we show that such a collective action problem does indeed undermine the competitive ability of large groups. Focal capuchins were more likely to run away from territorial intrusions when their group had a numeric advantage; each one-individual increase in relative group size raised the odds of flight by 25%. However, interaction location had a more important impact on individuals' reactions, creating a strong home-field advantage. After controlling for relative group size, the odds that a focal animal fled were 91% lower in experiments that occurred in the center compared with on the edge of its group's range, whereas the odds that it rushed toward the speaker were more than sixfold higher. These location-dependent patterns of defection and cooperation create a competitive advantage for residents over intruders across a wide range of relative group sizes, which may stabilize range boundaries and provide a general explanation for howgroups ofwidely divergent sizes can coexist, even in the face of intense intergroup competition.

Original languageEnglish (US)
Pages (from-to)501-505
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume109
Issue number2
DOIs
StatePublished - Jan 10 2012
Externally publishedYes

    Fingerprint

Keywords

  • Barro Colorado Island
  • Intergroup aggression
  • Panama
  • Resource holding potential
  • Territoriality

ASJC Scopus subject areas

  • General

Cite this