The essence of the concept of r- and K-selection is that organisms strive to maximize their fitness for survival in either uncrowded (r-selection) or crowded (K-selection) environments. Fitness is defined following ecological convention as the proportion of genes left in the population gene pool (Pianka, 1983, p. 10). The terms r and K refer, respectively, to the maximum specific rate of increase (maximum specific growth rate minus minimum specific death rate) of an organism and to the density of individuals that a given environment can support at the population equilibrium. Since both r and K can vary within a species and are subject to modification, the division of natural selection into r- and K-selection is of considerable basic interest in evolutionary ecology.