Advances in higher-order interactions between organisms

Abstract

It is well known that interactions between organisms are the key to species coexistence and biodiversity maintenance. Traditional studies focused overwhelmingly on direct interactions between species pairs, ignoring the more complex indirect interactions. In this review, we first distinguished two types of indirect interactions, i.e. interaction chains and higher-order interactions (HOIs). Then we reviewed the definition of higher-order interactions including the hard-HOIs and soft-HOIs, and the studies of HOIs among multiple trophic levels and within a single trophic level. In the food-web literature (among multiple trophic levels), ecologists widely studied the properties, mechanisms, pathways and experimental evidence of HOIs. Recently, there is an increasing interest in HOIs within a single trophic level. Therefore, we further introduced the significance and quantification of individual-level HOIs within a single trophic level. Not only can individual-level HOIs reconcile the hard-HOIs and soft-HOIs, but also allow us to consider variatons between individuals (e.g. individual size and spatial distribution). Finally, we proposed some promising research directions of HOIs including but not limited to: testing the prevalence and relative importance of HOIs in natural communities, exploring the mechanisms of HOIs and integrating HOIs to existing theories of community ecology. Inclusion of HOIs will help us understand the mechanisms of species coexistence and biodiversity maintenance profoundly and comprehensively, enrich and refine the theoretical framework of community ecology, and lay the foundation for biodiversity conservation and management of ecosystems in the Anthropocene.