Understanding human-commensalism through an ecological and evolutionary framework

Human-commensalism has been intuitively characterised as an interspecific interaction whereby non-human individuals benefit from tight associations with anthropogenic environments. However, a clear definition of human-commensalism, rooted within an ecological and evolutionary framework, has yet to be proposed. Here, we define human-commensalism as a population-level dependence on anthropogenic resources, associated with genetic differentiation from the ancestral, non-commensal form. Such a definition helps us to understand the origins of human-commensalism and the pace and form of adaptation to anthropogenic niches, and may enable the prediction of future evolution in an increasingly human-modified world. Our discussion encourages greater consideration of the spatial and temporal complexity in anthropogenic niches, promoting a nuanced consideration of human-commensal populations when formulating research questions.