Interference Competition and the Coexistence of Two Competitors on a Single Limiting Resource

This paper proposes a mechanistic model of competition between two species for a single, nonaccumulating food resource. Actual organisms to which it may apply are sessile species like terrestrial plants and suspension—feeding benthic marine invertebrates whose energy source rains down upon them from the surrounding environment. The model's assumptions described general functions involving population growth, resource consumption, resource availability, and interference. The population consequences of competition thereby arise in a specified way from the properties of individual organisms. The generality of thevarious component functions allows them to accomodate a wide range of species' morphological, physiological, and behavioral properties as wells as relevant features of the physical environment. Accordingly, the overall model potentially approximates a correspondingly broad array of natural cases of competition. This model demonstrates the theoretical possibility that two species jointly limited by the same energy resource can coexist at a globally stable equilibriumpoint. The proof of this assertion involves standard isocline analysis. It reveals that, in this case, coexistence depends upon species' interference as well as resource exploitation properties. In particular, the two can coexist if each species interferes less with resource acquistion by the other than with resource acquisition by itself and if this difference is great enough to overwhelm the advantage of the more efficient exploitation competitor. The model includes the effects of space competition and abiotic disturbances. Field testing is discussed.