Intransitive competition is common across five major taxonomic groups and is driven by productivity, competitive rank and functional traits

Abstract

Competition can be fully hierarchical or intransitive, and this degree of hierarchy is driven by multiple factors, including environmental conditions, the functional traits of the species involved or the topology of competition networks. Studies simultaneously analysing these drivers of competition hierarchy are rare. Additionally, organisms compete either directly or via interference competition for resources or space, within a local neighbourhood or across the habitat. Therefore, the drivers of competition could change accordingly and depend on the taxa studied. We performed the first multi‐taxon study on pairwise competition across major taxonomic groups, including experiments with vascular plants, mosses, saprobic fungi, aquatic protists and soil bacteria. We evaluated how general is competition intransitivity from the pairwise competition matrix including all species and also for each possible three‐species combination (triplets). We then examined which species were likely to engage in competitive loops and the effects of environmental conditions, competitive rank and functional traits on intransitive competition. We found some degree of competition intransitivity in all taxa studied, with 38% to 5% of triplets being intransitive. Variance in competitive rank between species and more fertile conditions strongly reduced intransitivity, with triplets composed of species differing widely in their competitive ranks much less likely to be intransitive. Including functional traits of the species involved more than doubled the variation explained compared to models including competitive rank only. Both trait means and variance within triplets affected the odds of them being intransitive. However, the traits responsible and the direction of trait effects varied widely between taxa, suggesting that traits can have a wide variety of effects on competition. Synthesis. We evaluated the drivers of competition across multiple taxa and showed that productivity and competitive rank are fundamental drivers of intransitivity. We also showed that not only the functional traits of each species, but also those of the accompanying species, determine competition intransitivity. Intransitive competition is common across multiple taxa but can dampen under fertile conditions or for those species with large variance in their competitive abilities. This provides a first step towards predicting the prevalence of intransitive competition in natural communities.

Functional traits and environmental characteristics drive the degree of competitive intransitivity in European saltmarsh plant communities

“…In this respect, Soliveres et al. () reported intransitive competition to be less likely under fertile habitat conditions. Nonetheless, nitrogen and carbon were positively linked to α‐ and β‐diversity (Figure a,b).…”

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

“…() and Soliveres et al. () refute this hypothesis using a variety of approaches. These three studies show more intransitivity under drier or unfertile conditions, meaning they find, in fact, that competition tends to be more hierarchical under fertile and productive conditions (see also Soliveres et al., ).…”

“…Evidence for this idea is mostly indirect, with studies on mobile taxa including protists (Carrara, Giometto, Seymour, Rinaldo, & Altermatt, ), ants (LeBrun, ), flies (Ulrich et al., ), fish (Henriksson et al., ) and birds (Miller et al., ) showing competition to be strongly hierarchical, whereas studies on sessile organisms more often show intransitive competition (Bowker et al., ; Buss, ; Dormann, ; Soliveres et al., ). However, it is easy to find evidence against this apparently general pattern, as shown by the first multi‐taxa experiment testing this notion, published in this issue (Soliveres et al., ). In addition, mobile organisms, such as lizards or plankton, are paradigmatic examples of intransitive competition (Huisman & Weissing, ; Sinervo & Lively, ).…”

“…Soliveres et al. () also show that intransitivity is related to the functional traits not only of the target species but also of those with which it is competing (see also Kunstler et al., ). Interestingly, clear relationships between functional traits and competitive dominance have been observed in a number of taxa when competition is hierarchical (Kunstler et al., ; LeBrun, ; Liouw, Di Martino, Voje, Rust, & Taylor, ; Miller et al., ), but a study in this issue suggests that these relationships may dampen when competition is intransitive (Soliveres et al., ).…”

Bryophyte and macrolichen diversity show contrasting elevation relationships and are negatively affected by disturbances in laurel forests of Madeira island

“…This is particularly true for the laurel forest on Madeira island (Capelo et al., ). As cover and biomass of macrolichens strongly increase with elevation (personal observation SB), the decrease of bryophyte species richness from intermediate to high‐elevation areas might also be attributed to competitive exclusion of some bryophytes by fast‐growing macrolichen species (Ruas, Bergamini, Carvalho, Fontinha, & Sim‐Sim, ), which might be driven by changes in productivity and functional traits of the accompanying species (Soliveres et al., ). However, this assumption needs further exploration.…”