Numerical simulation results. Time courses of the variables x1 (a) and x2 (b) obtained by numerical simulations of the model (7). The different plots result from simulations with different initial numeric values in D1, and different sets of parameter numeric values but fulfilling the same inequalities that characterize the qualitative trajectory QB4. The horizontal continuous lines in correspondence to threshold values should facilitate the comparison with Fig. 6. All plots related to each variable are qualitatively abstracted by the related plot in Fig. 6.