FIG. 4.

Basins of attraction and nullclines. Panel showing the separatrices and nullclines $\left(d{x}_H/dt=0,d{x}_S/dt=0,d{x}_R/dt=0\right)$ through the balanced fitness interior fixed point that determines the basin boundaries of attraction of the S state and the R states. The interior fixed point is the one in which each of the subpopulation fitness levels exactly matches the average fitness of the entire population. Filled circles are stable, unfilled circles are unstable.