How does facilitation influence the outcome of species interactions?

Abstract

Abstract Research on facilitation has not had the advantage of being explicitly underpinned by mathematical population dynamic theory. This has limited understanding of the role of facilitation on ecological dynamics and the integration of facilitation into general theory. I show that facilitative interactions can be classified into four categories likely to be dynamically similar to interaction types for which population‐dynamic theory does exist. This classification provides a useful population‐dynamic foundation for facilitation studies and reveals several fundamental questions unanswered by existing empirical work. While facilitation has typically been excluded from studies of ‘competitive’ coexistence, I also describe how coexistence theory does not always default to the assumption that species only compete; recent developments in coexistence theory fully accommodate the potentially important influence of facilitation. Simple models of multispecies population dynamics emphasize the importance of reciprocal interspecific interactions, intraspecific interactions, and density dependence for understanding the outcome of facilitative interactions. I point to approaches for aligning future empirical studies of facilitation with these features. Synthesis: Closely aligning at least some future empirical work on facilitation with existing mathematical population dynamic theory will further improve understanding of the effects of facilitation on ecological dynamics.