Examining the link between competition and negative co‐occurrence patterns

Abstract

Negative species co‐occurrence patterns have long intrigued ecologists because of their potential link to competition. Although manipulative field experiments have consistently revealed evidence of competition in natural communities, there is little evidence that this competition produces negative co‐occurrence patterns. Evidence does suggest that abiotic variation, dispersal limitation and herbivory can contribute to patterns of negative co‐occurrence among species; it is possible these influences have obscured a link with competition. Here, we test for a connection between negative co‐occurrence and competition by examining a small‐scale, relatively homogeneous old‐field plant community where the influence of abiotic variation was likely to be minimal and we accounted for the impact of herbivory with an herbivore exclosure treatment. Using three years of data (two biennial periods), we tested whether negatively co‐occurring pairs of species, when occasionally found together, experienced asymmetric abundance decline more frequently than positively co‐occurring pairs, for which there is no such expectation. We found no evidence that negatively co‐occurring pairs consistently suffered asymmetric abundance decline more frequently than positively co‐occurring pairs, providing no evidence that competition is a primary driver of negative co‐occurrence patterns in this community. Our results were consistent across control and herbivore exclosure treatments, suggesting that herbivores are not driving patterns of negative species co‐occurrence in this community. Any influence of competition or herbivory on co‐occurrence patterns is small enough that it is obscured by other factors such as substrate heterogeneity, dispersal and differential species responses to climatic variation through time. We interpret our results as providing evidence that competition is not responsible for producing negative co‐occurrence patterns in our study community and suggest that this may be the case more broadly.

Co‐occurrence is not evidence of ecological interactions

“…Although they are often time consuming and costly, they can increase our knowledge on interactions while remaining in the world of co‐occurrences. As an example, Brazeau & Schamp (2019) have recently studied experimentally the link between competition and negative co‐occurrence for flowering plants. Similarly, Kopelke et al (2017) gathered a large data set directly recording the interaction between willow tree species and sawflies, a group of parasites feeding on willow leaves.…”

“…While some recent studies have unveiled such a regular signal (e.g. Gotelli et al, 2010; Cardillo, 2011), other have shown that the signal is blurred and diluted in complex networks (Cazelles et al, 2016) or even absent (Brazeau & Schamp, 2019) and thus, the existence of a signal and properties thereof are still debated.…”

“…In the past 2 years, no less than four examinations have been proposed of recent statistical approaches used to infer species associations from presence–absence data (Barner et al, 2018; Freilich et al, 2018; Thurman et al, 2019; Brazeau & Schamp, 2019). Those studies focused on specific sets of species that met two criteria: (1) regional scale species presence–absence data were available and (2) biotic interactions among the species considered were documented a priori .…”

Ignoring social distancing: advances in understanding multi-species bacterial interactions

“…Owing to the correlative nature of network interaction, the complexity and non-linear dynamics of communities inferring interactions from covariance should be viewed with skepticism until coupling with empirical data to prove interactions (i.e. colocalization, stable isotope labeling, and co-culturing assays) 84 , 85 . This is illustrated by recent papers incorporating known metabolite transport, usage, and production with species co-occurrence into a network and finding both known and yet-to-be-confirmed interactions ( Figure 2C ) 80 , 81 .…”

Trait-similarity and trait-hierarchy jointly determine co-occurrences of resident and invasive ant species

“…2) co-occurrence patterns similar to those we observed. However, we appreciate that such patterns 430 may also be generated by other ecological processes (Brazeau & Schamp, 2019). Thus, in order 431 to strengthen inferences for particular assembly processes which could be at play, we explicitly 432 scrutinized species' co-occurrence relationships in light of their ecological differences (i.e., 433 traits) within the context of classical and contemporary theories on interspecific competition 434 ( Fig.…”