Fig. 4.

Phase portrait of Eqs. (2) for a=0.8, b=10, c=1, d=9, $r_1=1$, and $r_2=5$. All trajectories converge to an attracting limit cycle. Two exemplary trajectories (bold curves), starting near the monomorphic equilibria (0.8,0) and (0,9), were simulated. They approach a stable limit cycle around the internal equilibrium.