Trait‐similarity and trait‐hierarchy jointly determine fine‐scale spatial associations of resident and invasive ant species

Mark K L Wong,Owen T Lewis,Toby P N Tsang,Benoit Guénard

doi:10.1111/ecog.05505

Abstract

Interspecific competition, a dominant process structuring ecological communities, is influenced by species' phenotypic differences. Limiting similarity theory holds that species with similar traits should compete intensely (‘trait‐similarity'). In contrast, competing theories including modern coexistence theory emphasize that species with traits conferring competitive advantages should outcompete others (‘trait‐hierarchy'). Either or both of these mechanisms may drive competitive exclusion, but their relative importance and interacting effects are rarely studied. Here, we explore empirically whether trait‐similarity and trait‐hierarchy can explain fine‐scale spatial associations observed between invasive and native ant species in a tropical assemblage. We find that pairwise co‐occurrences between the invasive red imported fire ant Solenopsis invicta and 28 other species across relatively homogenous grasslands can be explained largely by an interaction of trait‐similarity and trait‐hierarchy in a single morphological trait, relative pronotum width. Specifically, higher trait‐hierarchy values are associated with negative co‐occurrences; however, these effects are counteracted when species are increasingly dissimilar in their trait ranges. These findings are consistent with the notion that limiting similarity and competitive hierarchies are interactive rather than discrete mechanisms driving competitive exclusion.

Highlights

Interspecific competition, a primary driver of community assembly and biodiversity patterns, is a process that is both well-known and yet stubbornly enigmatic
Patterns consistent with competitive interactions have been widely documented in a variety of ecological communities (Schoener 1974, Calatayud et al 2020), but precisely how phenotypic differences between species determine the nature of competitive exclusion has remained highly contested (D’Andrea and Ostling 2016)
We focused on differences in individual traits, as combining all traits into a composite index requires the assumption that all traits affect interspecific competition uniformly

Summary

Introduction

Interspecific competition, a primary driver of community assembly and biodiversity patterns, is a process that is both well-known and yet stubbornly enigmatic. Patterns consistent with competitive interactions have been widely documented in a variety of ecological communities (Schoener 1974, Calatayud et al 2020), but precisely how phenotypic differences between species determine the nature of competitive exclusion has remained highly contested (D’Andrea and Ostling 2016). Resource overlap (Schoener 1974) and phylogenetic distances (Mayfield and Levine 2010) between species as proxies for their niche dissimilarity; recent work emphasized differences in species’ functional traits (D’Andrea and Ostling 2016). The trait-similarity hypothesis predicts that the likelihood of co-occurrence will decrease with increasing overlap in trait space, such that co-occurring species display ‘overdispersion’: high absolute dissimilarity in trait space (Fig. 1a)

Methods

Results

Conclusion