The Stable Coexistence of Two Competitors for One Resource

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Abstract
A mechanistic model of interspecies competition expresses population growth in terms of resource consumption rate, consumption in terms of resource encounter rate and encounters in terms of resource searching rate and resource abundance, which themselves depend on population sizes. Standard isocline analysis reveals that it is possible, under a variety of conditions on the component functions, for 1 resource to support 2 competing species at globally stable equilbrium population sizes. Under this formulation, stable coexistence requires a suitable form of interference competition. The possiblities include greater intraspecific than interspecific interference in resource searching rates or resource encounter rates and a pattern of internal energy allocation that ensures that the less aggressive interference competitor is the more efficient resource consumer. Hypothetical examples are phrased in terms of actively foraging animals, terrestrial plants, and suspension-feeding marine benthic invertebrates. The mechanistic nature of the model helps resolve long-standing semantic difficulties concerning limiting resources that arise from the Lotka-Volterra model; it encourages both future theoretical extensions and empirical testing.