Figure 7.

Projection of the slow manifold Σ on the space (u₁, a₁, a₂). System (2.1)’s parameters are β = 1.1, g = 0.5, θ = 0.2, r = 10, and I = 1.5 (A–C), respectively, I = 1 (D–F). The curve $\mathcal{SN}$ of saddle-nodes (jumping points) is represented in blue-red (C, F). Nullclines ${\mathcal{N}}_1$ (magenta) and ${\mathcal{N}}_2$ (black curve) intersect in three points for (B) I = 1.5 and (E) I = 1. However, either the equilibrium points can all lie on the middle branch of Σ (A), that is, inside the curve of saddle-nodes (C), or two equilibrium points can move to the lateral branches, outside of $\mathcal{SN}$ (D, F).