epidemic (SIRS),
and competition,
As these models are introduced, the text briefly considers relevant phase plane and equilibrium ideas.
A detailed study of the phase plane begins in chapter 7, Graphical Tools for Two Dimensions, using the pendulum model developed in section 5.2. The SIRS model joins the pendulum in section 7.2, Nullclines and Local Linearization, p. 343-350, and one of its phase plane diagrams appears on the cover of the book.
All three multiple-species models appear in the exercises for section 7.2, Nullclines and Local Linearization, for section 8.1, Basic Definitions: Systems, and for section 8.3, Connections with the Phase Plane. As appropriate, these exercises request nullcline analyses and phase plane sketches, or they request the determination of equilibria and a linearized phase plane analysis about each. Students can reasonably be expected to complete such exercises, including providing a physical interpretation of the results, based on a prior exposure to a plausibility argument for just one of these models, say SIRS.