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.
Here I refer to the former as the (ideal) r-selection gradient:
The total selection gradient is proportional to the weighted average of the r-selection gradient and the K-selection gradient,
When the population density is so low that density effects are negligible, r-selection dominates K-selection.
The r-selection is generated by removing individuals randomly before reproduction every generation so that the population is kept at a low density that does not bring about a notable density effect (N = 50).
Figures 2a,b,c represent the results of r-selection. The evolutionary trajectories of the underlying characters and additive genetic variances and genetic correlation between [r.sub.ln] and [K.sub.ln] are derived with various genetic correlations between the underlying characters.
The evolutionary rate is dependent upon the genetic correlations of the characters in the same manner, but the rate of evolution is considerably slower than r-selection. With negligible genetic correlations (nearly 0), evolution by K-selection needs nearly 100 generations to reach the optimum.
To demonstrate how r-selection is effective, a single bout of strong disturbance is imposed upon the equilibrium population so that the population size decreases drastically in a certain generation.
But, if two phenotypes contribute to r or K exclusively (one of the phenotypes has a certain optimum for r-selection, but is selectively neutral for K-selection, and vice versa), the trade-off is obscured because the evolutionary increase of r may not be followed by an evolutionary decrease of K if the genetic correlation between the two phenotypes is nearly zero.
Under stable environments, K-selection is the major selective force and r-selection may be negligible.
Even if the demographic level of a population is usually so low that r-selection predominates over K-selection [Mathematical Expression Omitted], [Mathematical Expression Omitted]: the stationary density due to frequent disturbances or migration), the realized r-selection gradient is not necessarily large and may not be equivalent among characters of a single species or between the same characters of different species.