Figure 1.

(a) Directions of the vector field in the four regions I, II, III, and IV in the phase plane divided by the null clines Γ_u (green) and Γ_v (blue). Please refer to the text for description of the blue and green arrows. (b) Orbits in the phase plane for $\alpha =0.2$ starting at $(u,v)=(u(0),v(0))$ where u(0) = 0.4, 0.8, 1.5, 2.0, 2.5, 3.0, and $v(0)=0$, as well as the null clines Γ_u (green) and Γ_v (blue) (MATLAB model code provided in Supplementary Figure S1).