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霊長類行動学8. Scramble versus contest competition



  • competition - key is contestability
    • seems to be driven by greed, but really driven by limitation of resources
    • contest competition: fight for access to resource
      • e.g., 10人に一つのパイをあげる際、一箇所に固まっておく→取り合いして勝ったものが取りたいだけ得る。
    • scramble competition: rush to gain access to a share
      • e.g., divide into a piece and scatter -> 早い者勝ちで取り合う。
      • 動物園では餌を散らしてやることで、decrease aggression


  • each condition is associated with resources (food / females)
    • clumped like fruit -> contest competition
    • scattered like leaves -> scramble competition

Competition in Females

manifest as within group or between group
  • Availability of fruit depends on its abundance and party size in the teritorry
    • females actively defend territory from other groups


  • If fruit tree are limited in the whole area,
  • If fruit tree are abundant in the area
  • If number of fruits in the teritory are abundant
  • If number of fruit in the teritory are limited
Female Orangutan (Fruitgivore)


  • scrabmle competition
  • females are dispersed in environment

Female Chimp


  • classic scramble competition
  • group size is big

  • usually
    • eat fruit
  • rainy season
    • keep eating fruits, keeping scramble competition, by dispersing more.

Female Gorilla


  • scramble competition
  • group size is constant

  • usually
    • eat fruit
  • Rainy season
    • start eating leaves
    • not compete over resources

Female Gibbons


  • strict territory
  • between group scramble
    • find territory as scramble
  • within group contest
    • whithin the territory, contest competition

Female Galagos


  • strict territory
  • classic contest competition even though they eat insects

  • in some species, the style of comtetition changes correlating with the group size.
    • in some species, they swith contest and scramble competition when the population gets too big in the territory

Competition in Males

  • more complected
  • female are the resources for male
  • contest style changes depending on
    • female clumped
    • female dispersed

  • most male engages in contest competition,
Male Gibbon
  • scramble competition - one of few exceptions


Male Brachyteles arachnoides (めちゃくちゃなやつら)
  • scramble competition - another exception
    • sperm compeition (sexual selection)
    • polygynyandry

Male Chimp
  • within group contest competition - they form hierarchy
  • Strong between group contest competition - by defending territory.

Male Gorilla
  • if limited dispersed resource (feamale)
    • strong contest competition
  • acquisition of territory is scramble competition
    • once one decides his territory, he will be fine.



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