Everything you always wanted to know about intransitive competition but were afraid to ask

Abstract

1. Over 40 years after the introduction of the concept into ecology, intransitive (i.e. non-hierarchical) competition remains overlooked by ecological theory, despite theoretical work showing it could be a major driver of species coexistence. 2. This special feature presents six studies, including models, reviews, experimental studies and large-scale observational studies. Collectively, these studies help to (i) link intransitive competition with short- and long-term coexistence and with other ecological patterns, (ii) evaluate the conditions under which intransitivity is more common and (iii) determine how best to quantify the degree of intransitivity. 3. The studies in this special feature show the generality of intransitive competition in nature, explore interactions between intransitivity and other coexistence mechanisms, and illustrate the effect of environmental conditions (drought, shade, fertility) on intransitivity and coexistence. They also show which metrics best quantify intransitivity and highlight the importance of adopting a more continuous view of competition as varying from strongly transitive to strongly intransitive. The studies also examine relationships between intransitivity and functional diversity and explore the evolution of intransitivity over time. 4. Synthesis. The studies presented here advance the field by integrating intransitive competition into species coexistence and general ecological theory. We also highlight important research gaps that will hopefully inspire the next generation of studies in this topic.