title: Intransitivity is infrequent and fails to promote annual plant coexistence without pairwise niche differences.
abstract: Intransitive competition is often projected to be a widespread mechanism of species coexistence in ecological communities. However, it is unknown how much of the coexistence we observe in nature results from this mechanism when species interactions are also stabilized by pairwise niche differences. We combined field-parameterized models of competition among 18 annual plant species with tools from network theory to quantify the prevalence of intransitive competitive relationships. We then analyzed the predicted outcome of competitive interactions with and without pairwise niche differences. Intransitive competition was found for just 15-19% of the 816 possible triplets, and this mechanism was never sufficient to stabilize the coexistence of the triplet when the pair-wise niche differences between competitors were removed. Of the transitive and intransitive triplets, only four were predicted to coexist and these were more similar in multidimensional trait space defined by 11 functional traits than non-coexisting triplets. Our results argue that intransitive competition may be less frequent than recently posed, and that even when it does operate, pairwise niche differences may be key to possible coexistence.
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC), Av. Reina Mercedes 10, E-41080, Sevilla, Spain.
authors.forename: Oscar
authors.initials: O
authors.lastname: Godoy
authors.affiliation: Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Stouffer
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 621 Charles E. Young Drive South, Los Angeles, California, 90095, USA.
authors.forename: Nathan J B
authors.initials: NJB
authors.lastname: Kraft
authors.affiliation: Institute of Integrative Biology, ETH Zurich, Universitaetstrasse 16, 8092, Zurich, Switzerland.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Levine
mesh_terms: D017753:Ecosystem; D008954:Models, Biological; D010641:Phenotype; D010944:Plants
keywords: California grasslands; competitive networks; functional traits; intransitive competition; rock-paper-scissors dynamics; stabilizing processes; trait dispersion patterns