Fig. 6.

Equilibria at the intersections of nullclines. a For intermediate values of k, there are three intersections, two of them representing stable equilibria. Solid red lines are projections of two trajectories of the full model, with initial states indicated by red dots and final stable states shown by black dots. The full trajectories approach the intersections of the q-nullcline (blue) and c-nullcline (black). b For large k there is only one intersection at the upper branch of the c-nullcline. Two trajectories with initial states near different branches of the c-nullcline both approach the unique intersection (black dot) on the upper branch. The scenario shown here corresponds to a Type I nullcline structure as described in the Additional file 1