Evolutionary stability of mutualism: Interspecific population regulation as an evolutionary stable strategy

J. Nathaniel Holland, Donald L. DeAngelis, Stewart T. Schultz

Research output: Contribution to journalArticlepeer-review

60 Scopus citations


Interspecific mutualisms are often vulnerable to instability because low benefit: cost ratios can rapidly lead to extinction or to the conversion of mutualism to parasite-host or predator-prey interactions. We hypothesize that the evolutionary stability of mutualism can depend on how benefits and costs to one mutualist vary with the population density of its partner, and that stability can be maintained if a mutualist can influence demographic rates and regulate the population density of its partner. We test this hypothesis in a model of mutualism with key features of senita cactus (Pachycereus schottii) - senita moth (Upiga virescens) interactions, in which benefits of pollination and costs of larval seed consumption to plant fitness depend on pollinator density. We show that plants can maximize their fitness by allocating resources to the production of excess flowers at the expense of fruit. Fruit abortion resulting from excess flower production reduces pre-adult survival of the pollinating seed-consumer, and maintains its density beneath a threshold that would destabilize the mutualism. Such a strategy of excess flower production and fruit abortion is convergent and evolutionarily stable against invasion by cheater plants that produce few flowers and abort few to no fruit. This novel mechanism of achieving evolutionarily stable mutualism, namely interspecific population regulation, is qualitatively different from other mechanisms invoking partner choice or selective rewards, and may be a general process that helps to preserve mutualistic interactions in nature.

Original languageEnglish (US)
Pages (from-to)1807-1814
Number of pages8
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1550
StatePublished - Sep 7 2004
Externally publishedYes


  • Fruit abortion
  • Hermaphrodite
  • Pollination
  • Population dynamics
  • Resource trade-offs
  • Sex allocation

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Agricultural and Biological Sciences (miscellaneous)


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