Can stochasticity reverse selection? Here we compare two models of altruism having the same per-capita growth rate, but differing in variance in per-capita growth (Model 1-red, Model 2-black).

As a consequence, this can lead to a stochastic reversal of selection for model 2 but not model 1. Subplots a-c: predicted stationary distribution for both models from Eq 1 (curve) compared to 2 × 104 simulations of the full stochastic process (circles) for decreasing habitat size, Ω (i.e., increasing levels of demographic stochasticity). The distribution is always skewed towards the non-altruist in model 1. For model 2 the distribution changes from being skewed towards the non-altruist to being skewed towards the altruist as demographic stochastic increases (i.e., a selective reversal occurs). Subplot d: magnitude of the selective reversal plotted against the cost of altruism. Parameters used were {β, d, κ, ν} = {3, 2.4, 1.2, 1}, with ϵ = 0.003 for subplots a-c.