A model system of four species with a unique equilibrium point

A four component model of two competing organisms, each with a specific parasite, has been exercised so as to investigate its equilibria. In addition to the equilibrium to which the model is known to return after moderate disturbance, severe perturbation led to a new steady state which had the appearance of an equilibrium but which was not maintained in the long term. Some discussion of what constitutes equilibrium and of stability of equilibria is presented.