Size asymmetry of resource competition and the structure of plant communities

Niv DeMalach*, Eli Zaady, Jacob Weiner, Ronen Kadmon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

116 Scopus citations


Plant communities show two general responses to gradients of soil resources: a decrease in species richness at high levels of resource availability and an associated shift in species composition from small and slow-growing species to large and fast-growing species. Models attempting to explain these responses have usually focused on a single pattern and provided contradicting predictions concerning the underlying mechanisms. We use an extension of Tilman's resource competition model to investigate the hypothesis that both patterns may originate from the size-asymmetric nature of light exploitation by competing plants. The only mechanism producing changes in species richness and species composition in our model is mortality due to competition. Under the framework of the model, asymmetric light exploitation is a necessary and sufficient condition to obtain the empirically observed responses of species richness and species composition to soil resource gradients. This theoretical result is robust to relaxing the simplifying assumptions of the model. Our model shows that the traits enhancing competitive superiority depend on the mode of resource exploitation: under symmetric exploitation, competitive superiority is achieved by tolerance of low resource levels, while under asymmetric exploitation, it is achieved by the ability to grow fast and attain a large size. This result indicates that a long-standing debate concerning the traits that enhance competitive superiority in plant communities (the ‘Grime–Tilman debate’) can be reduced into a single parameter of our model – the degree of asymmetry in resource competition. The model also explains the observed shift from below-ground to above-ground competition with increasing productivity, the associated increase in the asymmetry of competitive interactions and the increasing likelihood of competitive exclusion under high levels of productivity. None of these patterns could be obtained under symmetric competition in our model. Synthesis. The ability of the model to explain a wide range of observed patterns and the robustness of these predictions to its simplifying assumptions suggest that the size asymmetry of competition for light is a fundamental factor in determining the structure and diversity of plant communities.

Original languageAmerican English
Pages (from-to)899-910
Number of pages12
JournalJournal of Ecology
Issue number4
StatePublished - 1 Jul 2016

Bibliographical note

Publisher Copyright:
© 2016 The Authors. Journal of Ecology © 2016 British Ecological Society


  • Grime–Tilman debate
  • asymmetric light competition
  • coexistence
  • functional traits
  • plant height
  • productivity–diversity relationship
  • resource availability
  • species richness


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