Linking obligate mutualism models in an extended consumer-resource framework

Abstract

A simple model of obligate mutualist populations is presented in an extended consumer-resource (ECR) framework to resolve some of the deficiencies of traditional models. Varying parameters representing the costs of providing a mutualist benefit allows the model to smoothly and stably transition between many existing models of obligate mutualism. Varying density-independent mortality parameters allows us to include or exclude Allee effects, while varying an obligation parameter allows us to smoothly transition between facultative and obligate mutualism. Explicit and exact accounting of mutualism benefits, measured in terms of a finite total amount of cycling limiting resource, is shown to lead to population models that bridge between apparently incompatible models of obligate mutualism. This brings models of obligate mutualism into the Conservative Normal theoretical framework alongside models of competition, mixotrophy and predation.