Lycaenid butterflies and ants: two-species stable equilibria in mutualistic, commensal, and parasitic interactions

We present a two-species model that describes the population dynamics of mutualistic, commensal, and parasitic interactions between lycaenid butterflies and ants. The lycaenids affect the equilibrium density of their associated ants, whereas the ants influence both the growth rate and the equilibrium density of the butterflies. The model can describe obligate as well as facultative relationships on the part of the lycaenids, and even when the interaction is mutualistic, the model has globally stable equilibria. We suggest that this model has general applicability to other two-species interactions.