Figure 4. Selection may maintain diversity and increase extinction.

(a) GFP allele frequency dynamics in simulated populations when starting with five GFP invaders. Simulations were run under frequency-dependent (black) or frequency-independent selection (grey), where s=0.12–2.32 p+2.36 p² or s=0.108 (assumed constant and calculated with P=0.005), respectively (from Fig. 3c). The stable polymorphic equilibrium is rapidly reached at around 5% under frequency-dependent selection, while most fixations occurred by generation 100 under frequency-independent selection. (b) Enlargement of the dashed box in a for frequency-dependent selection. Several replicate populations face extinction even when their sizes were simulated with N=10³. (c) Expected probabilities of extinction and fixation estimated from the 1,000 simulated populations of a and b, under frequency-dependent selection or frequency-independent selection (black or grey lines). Frequency-dependent selection can increase extinctions when compared with frequency-independent selection after generation 50 (dashed lines). The triangle indicates the ultimate probability of extinction (infinite time) when using the approximation P_ext=e^−2s for frequency independence with large selection coefficients33.