Ecological Research

, Volume 21, Issue 5, pp 707–712 | Cite as

Size-asymmetric competition and size-asymmetric growth in a spatially explicit zone-of-influence model of plant competition

Original Article

Abstract

Size-asymmetric competition among plants is usually defined as resource pre-emption by larger individuals, but it is usually observed and measured as a disproportionate size advantage in the growth of larger individuals in crowded populations (“size-asymmetric growth”). We investigated the relationship between size-asymmetric competition and size-asymmetric growth in a spatially explicit, individual-based plant competition model based on overlapping zones of influence (ZOI). The ZOI of each plant is modeled as a circle, growing in two dimensions. The size asymmetry of competition is reflected in the rules for dividing up the overlapping areas. We grew simulated populations with different degrees of size-asymmetric competition and at different densities and analyzed the size dependency of individual growth by fitting coupled growth functions to individuals. The relationship between size and growth within the populations was summarized with a parameter that measures the size asymmetry of growth. Complete competitive symmetry (equal division of contested resources) at the local level results in a very slight size asymmetry in growth. This slight size asymmetry of growth did not increase with increasing density. Increased density resulted in increased growth asymmetry when resource competition at the local level was size asymmetric to any degree. Size-asymmetric growth can be strong evidence that competitive mechanisms are at least partially size asymmetric, but the degree of size-asymmetric growth is influenced by the intensity as well as the mode of competition. Intuitive concepts of size-asymmetric competition among individuals in spatial and nonspatial contexts are very different.

Keywords

Growth–size relationship Local competition Local density Neighborhood competition Size-dependent growth 

Notes

Acknowledgments

We thank two anonymous reviewers and editor Yoh Iwasa for helpful comments on the manuscript. This research was supported, in part, by a grant from the Danish Agricultural and Veterinary Research Council (53-00-0246).

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Copyright information

© The Ecological Society of Japan 2006

Authors and Affiliations

  1. 1.Department of EcologyRoyal Veterinary and Agricultural University, Rolighedsvej 21FrederiksbergDenmark
  2. 2.Department of Terrestrial EcologyNational Environmental Research Institute, Vejlsøvej 25SilkeborgDenmark

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