Theory of Fitness in a Heterogeneous Environment. I. The Fitness Set and Adaptive Function

Abstract

The mode of adaptation of a species (specialization vs. generalization, type of developmental flexibility, polymorphism, clines, polytypy) are considered to be adaptations to the statistical pattern of the environment in space and time. Each mode of adaptation is represented by a point in a multi-dimensional environment space (Fitness Set) and a measure of fitness is defined over that set (the Adaptive Function). The mode of adaptation which maximizes the Adaptive Function is regarded as optimal, and natural populations are assumed to differ among themselves in the same direction as their optima. Polymorphism is shown to be advantageous when temporal fluctuations of the environment are large compared to the tolerance of an individual, while local spatial heterogeneity favors specialization and race formation. When the environmental heterogeneity is small compared to the tolerance, a monomorphic unspecialized local population and continuous cline is optimal.