Schematic representation of the belt orbits (solid gray and black) and the planet orbit (red) at the different stages of the ACE simulations: (a) the initial, circular, unperturbed belt; (a, b) the belt perturbed by the planet, but not modified by collisions; (b) the belt modified by collisions, but not by the perturber; (b, c) the belt modified by both the perturber and collisions.