A perspective on stage‐structured mutualism and its community consequences

Abstract

Ontogenetic variation is the most fundamental biological aspect of an organism, and stage‐structured (size‐structured) prey–predator relationships have increasingly been studied for better understanding food webs. However, little is known about stage‐structured mutualism and its community consequences (i.e. when and where it occurs and how it matters in community ecology). This article aims to argue that mutualism can be viewed as inherently stage‐structured while drawing research attention to the little‐studied issue. First, to conceptualize stage‐structured mutualism, I present possible community modules, such as inter‐stage partner sharing, ontogenetic antagonism–mutualism coupling and ontogenetic partner shift, which are mechanistically obtained due to the ontogenetic variation in associated costs and benefits. A synthesis of the literature across different mutualisms (e.g. pollination, seed dispersal, nutritional and defensive) demonstrates that mutualism is commonly stage‐structured, and those examples can be categorized into the different community modules conceptualized above. To integrate structural diversity and complexity, I present a general theoretical framework for describing community dynamics mediated by stage‐structured mutualism. It can provide testable hypotheses regarding how stage‐specific partners can affect each other through the life history of a shared host and how they jointly determine the lifetime fitness of the host. For the establishment of the ontogenetic perspective of mutualism, both empirical and theoretical efforts are needed to collect and incorporate individual‐level interaction data into community ecology theories, which will provide valuable insights not only into mutualism‐mediated community dynamics but also into biodiversity conservation and ecosystem management.