Intrinsic Rate of Increase, Saturation Density, and Competitive Ability. II. The Evolution of Competitive Ability

Abstract

The concepts of natural selection and competition are distinguished, and the competition coefficients are rigorously defined; r-selection is not relevant to competition, but K-selection is a consequence of exploitative competition wherein consumers and resources are directly interconvertible. When only a single resource limits a population, competition coefficients are proportional to the ratio of saturation densities and are reciprocal. When several limiting resources exist, competition coefficients must be ≤1 and competitive exclusion will not occur. Under exploitative competition K and competitive ability are inversely related. Alpha-selection is defined as the evolutionary process by which competitive ability increases and refers to the acquisition of interference phenomena whereby individuals impair the reproductive rate dN/Ndt of competitors. Possession of interference mechanisms may require adjustments of energy budgets, so that α-selection is a mechanism of evolutionary reduction of r and K. Interference competition results in competitive exclusion because the competition coefficients are nonreciprocal and >1. Alpha-selection can occur at either low or high density, and hence may be a ubiquitous force in evolution. It is concluded that species dominance in competition can not in principle be predicted from knowledge of r or K alone.