Alternative Models of Character Displacement and Niche Shift. 2. Displacement when There is Competition for a Single Resource

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Abstract
Character displacement or nongenetic niche shift, when competitors become sympatric, can result from changes in the absolute abundance of the resources available, as well as from changes in the relative abundance of different types. A model of competition for a single resource by two species of consumers is used to illustrate the range of possible directions of phenotypic change that can occur when the main effect of competition is a change in the absolute resource abundance at equilibrium. Divergence, convergence, and parallel change are all possible responses to competition in sympatry, depending on the type and magnitude of cost involved in increasing the functional response. Parallel change may be the most common mode of displacement for similar species. These adaptive responses to competition may result in an increase or a decrease in the strength of the competitive interaction between the species.