MACARTHUR and Wilson1 coined the terms r selection and K selection to describe two general kinds of selection they believed could be functioning in nature (K refers to carrying capacity and r to maximal intrinsic rate of natural increase, rm). As originally defined, the r and K selection concepts postulated that alternative genotypes within a species possessed somewhat divergent life history characteristics : genotypes with a high rm were suggested to have a relatively low K and vice versa 1. Thus, r selection occurs in a fluctuating environment when there is no crowding and it is more important to increase the size of the population. K selection occurs in stable environments when population size is always near the maximum and increasing efficiency in resource use is required for the production of a few but extremely fit offspring. Pianka2 extended these concepts to include comparisons of individuals of different species. He postulated that no organism is completely r selected or completely K selected, but all must reach some compromise between the two extremes. Thus, a given species could be visualised along an r-K continuum and identified by a set of r and K characteristics2.