A Simple Model of Mutualism

A population of mutualists must eventually reach a maximum carrying capacity because of intraspecific competition for limited resources, even if another population of mutualists is present in excess. The model presented reflects this, so allowing a stable equilibrium to be reached. Either facultative or obligate use of one mutualist by another is seen to be independent of whether the former makes facultative or obligate use of the latter. Given that a mutualism may occur, facultative use by both populations will inevitably lead to a stable equilibrium no matter the initial densities of the populations; but if one population makes obligate use of the other, then thresholds may occur such that the mutualism will be sensitive to environmental perturbations.