Downstream resource leakage a necessary condition for the stress-gradient hypothesis in processing chain commensalisms.

The stress-gradient hypothesis (SGH) in ecology predicts that the strength and frequency of positive interspecific interactions, including processing chain commensalisms (PCCs), increase with environmental stress. Although observed in some empirical PCC studies, a recent theoretical study of PCCs using a consumer-resource-type model found that, given the model's assumptions, the SGH never occurs. To investigate if this is a true reflection of PCCs or merely an artefact of the model, in this study, we modified this earlier model formulation by incorporating generalized, monotonically increasing resource uptake functions in place of linear functions, and added a term to represent the spontaneous leakage of the downstream resource to the environment.