Fig 2. Traveling fitness landscape and its linear approximation near the infected peak.

Red curve: analytic result (Eq 7). Gray circles: Monte-Carlo simulation based on Eq 1. Black line: linear approximation with the average selection coefficient σ = 0.066 (Eq 8). Parameters as in Fig 1: R₀ = 2, a = 9, U_b = 5.8 × 10⁻⁶, N = 10⁸. For the accuracy of linear approximation, see S1 Fig.