This tradeoff between quantity and quality has resulted in different reproductive strategies, e.g., r- and K-selection (Pianka 1970).
On r- and K-Selection. American Naturalist 104:592-597.Skow, C.D.
r- and K-selection in experimental populations of Escherichia coli Science 202:1201-1203.
Trade-off between r-selection and K-selection in Drosophila populations.
These observations indicate that r- and K-selection, based on simple effects of density alone, is not so potent of an environmental force moulding general life-history "strategy" (i.e., coordinated evolution of the most life-history traits together) as has been postulated.
The differences in egg-to-adult viability between the r- and K-selection regimes and between the Y- and O-selection regimes are shown in Figure 1.
No interactions between the r- and K-selection regimes and larval rearing density were observed in either sex.
In the comparison of the r- and K-selection regimes we found a negative association between preadult developmental time, on one hand, and adult body mass and total fecundity, on the other, whereas longevity of the females (but not the males) remained unaffected.
Previous theoretical studies based on one-locus, two-allele population genetic models have shown that r- and K-selection can cause gene frequency changes with realistic assumptions on the allelic effect of genes and demography.
With this measure of fitness, selection on phenotypes is decomposed into two subsets of selection (r-selection gradients and K-selection gradients), which describe selective forces under different phases of population growth.
This study presents a quantitative genetic model describing evolutionary changes in the underlying phenotypes by density-dependent selection based on this view of r- and K-selection. The rates of evolutionary changes in r and K are also derived.
and the latter as the (ideal) K-selection gradient: