The Life-History Approach to Physiological Ecology

Abstract

In the evolutionary process, new alleles are continually being created by mutation and they either spread or, generally, disappear, according to whether they are selected for or against (Fig. 1). The key characteristic of an allele is, therefore, whether or not it will spread. This can be measured by its per capita rate of increase. For example if there are 1000 copies of an allele at time t and 1003 at time t+1, then the per capita rate of increase is approximately 3/1000 = 0 003. Strictly we should measure it as an instantaneous rate of increase, and this can be obtained as loge (1.003) = 0-002996. Clearly alleles with greatest spreading power are those with highest rates of increase. They are most likely to be able to enter a population, and once there are most likely to resist invasion by competitor alleles, assuming their superiority is not frequency dependent. Such alleles are, therefore, the likely end products of evolution. Once fixed in the population, their long-term rate of increase is, of course, necessarily zero. In summary, their properties are (a) maximum rate of increase, while at the same time (b) this rate of increase is zero. In a stable environment, these are the properties we would expect alleles to have.