Effects of competitive asymmetry on a local density model of plant interference

Stephen Wilson Pacala, J. Weiner

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39 Scopus citations


Although competition between plants is usually asymmetric (i.e. larger plants have a disproportionate effect on smaller plants) almost all models of plant competition at the local level have assumed symmetric competition. We add a simple version of competitive asymmetry to the local density neighborhood models of plant interference and population dynamics developed by Pacala & Silander (1985, Am. Nat.125, 385-411; 1987, Oikos48, 217-224) by assuming that plants within a neighborhood can be put in a linear dominance hierarchy based upon their initial size. The size of a focal plant is a function of the number of dominant and the number of subordinate neighbors within its neighborhood, with subordinate neighbors having less of an effect than dominant ones. Asymmetry prevents precipitous changes in focal plant size with changes in local density, making the relationship between focal plant size and local density hyperbolic, even if the symmetric model is not hyperbolic. Thus, asymmetry makes the model conform to the law of constant final yield, irrespective of the form of the relationship between plant size and local crowding. Asymmetry also prevents population dynamic oscillations in the model in cases in which it would occur in the absence of asymmetry. The results show that asymmetry has major effects on a model of local interference in plants, and point to the importance of including it in such models.

Original languageEnglish (US)
Pages (from-to)165-179
Number of pages15
JournalJournal of Theoretical Biology
Issue number2
StatePublished - Mar 21 1991

All Science Journal Classification (ASJC) codes

  • General Immunology and Microbiology
  • Applied Mathematics
  • General Biochemistry, Genetics and Molecular Biology
  • General Agricultural and Biological Sciences
  • Statistics and Probability
  • Modeling and Simulation


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