Figure 2.

Fixation probability of the mutant type, A, as a function of (half) the width of the mutant fitness distribution, Δ_a. The fitness values for the mutant and resident are uniformly distributed on $[\overline{a}-{\mathrm{\Delta }}_a,\overline{a}+{\mathrm{\Delta }}_a]$ and $[\overline{b}-{\mathrm{\Delta }}_b,\overline{b}+{\mathrm{\Delta }}_b]$, respectively (solid line). Similarly, for a bimodal distribution, the fitness values for the mutant and resident are $\overline{a}-{\mathrm{\Delta }}_a$ or $\overline{a}+{\mathrm{\Delta }}_a$ and $\overline{b}-{\mathrm{\Delta }}_b$ and $\overline{b}+{\mathrm{\Delta }}_b$, respectively, each with probability $\frac{1}{2}$ (dashed lines). These values, Δ_a and Δ_b, are measures of mutant and resident heterogeneity, respectively. The population size is N = 50 and the solid/dashed lines indicate the analytical predictions from equation (3.8). As Δ_a grows, a beneficial mutant’s fixation probability decreases. However, this fixation probability does not change as Δ_b varies (not shown in the figure).