Coevolution in Ecological Systems III. Coadaptation and Equilibrium Population Size

Abstract

The effort toward uniting evolutionary theory with ecological theory has been plagued from the beginning by a conflict between the optimization criterion in evolutionary theory and criteria from ecological theory. In evolutionary theory, natural selection is viewed as producing traits which maximize the fitness of the individuals carrying them relative to the fitness of individuals with alternative traits. The criterion of fitness maximization is often used uncritically and incorrectly in evolutionary theory, especially in sociobiological contexts, but it can sometimes be justified. One of many examples where it is justifiable is discussed below. The problem to be discussed in this paper, however, does not lie with the criterion of fitness maximization in itself, but with the fact that optimum strategies computed according to the fitness criterion do not generally coincide with optimum strategies determined from various ecological optimization criteria. Specifically, one common type of optimum ecological strategy maximizes the abundance of a population. In ecology it is natural to ask what strategies of resource use and allocation will lead to the highest population size, i.e., what predation rate leads to optimum harvesting of the prey, how much energy should prey allocate to predator defense, etc. For these questions, the criterion is the maximization of population size. The optimum predation rate is that which yields the highest sustainable yield, and analogously for the optimum prey defense.