Illustration of adaptation in the phase plane.

<p>Squares denote the stable equilibrium states. Arrows starting at point stand for the rate of change of the two diameters. (A) phase plane of a parallel vessel system. In the three stable equilibrium states, at least one diameter is zero, i.e., at most one vessel can survive. (B) phase plane of a parallel system with switches (fixed OTRs). There is a new stable equilibrium in which neither diameter vanishes, i.e., both vessels survive.