Competitive intransitivity and size-frequency distributions of interacting populations

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Abstract
The competitive ranking of 3 marine sessile organisms [Onychocella alula, Antropora tincta and Neogoniolithon rugulosum] was determined from overgrowth observations and was intransitive. Overgrowth results were dependent upon relative vertical relief which, in turn, was related to colony area. Discriminant function analysis demonstrates that competitive rankings can be largely predicted based on knowledge of the size-frequency distribution of interacting populations. Because size increases with age for these species, size-dependent competition implies age-dependent competition. The role of age structure in determining the results of interspecific interactions has been curiously neglected, particularly as it relates to competitive ability. The age dependence of competitive ability suggests the occurrence of intransitivity in purely exploitative systems, a mechanism for frequency-dependent behavior, the production of limit cycles and the possibility of size refugia.