DECOMPOSITION ANALYSIS OF COMPETITIVE SYMMETRY AND SIZE STRUCTURE DYNAMICS

An analysis is introduced, based on the decomposition of relative grow th rates, to examine the mode of competition (i.e. whether competition is symmetric or asymmetric), the size-dependence of growth, and their interdependence. In particular, the basis for two commonly held Views is examined: (1) that the type of resource limitation determines the mode of competition, and (2) that asymmetric competition always leads to size-divergence between unequal competitors. It is shown that in he ld-grown miller plants, competition for light was symmetric at low den sity and asymmetric at high density. However, size variation at low de nsity decreased during growth, because small plants had greater relati ve growth rates than larger plants. Size variation stayed constant at high density, since plants of all sizes had equal average relative gro wth rates. Based on these results and a general discussion, it is prop osed that the type of resource limitation does not determine the mode of competition. Competition for light can be symmetric, and foraging f or heterogeneously distributed soil resources can produce asymmetric c ompetition below-ground. Furthermore, the mode of competition alone do es not determine size structure dynamics. Size-dependence of resource conversion efficiency and allocation can modify the effects of resourc e uptake on growth. (C) 1996 Annals of Botany Company