The roles of amensalistic and commensalistic interactions in large ecological network stability.

Akihiko Mougi

doi:10.1038/srep29929

Abstract

Ecological communities comprise diverse species and their interactions. Notably, ecological and evolutionary studies have revealed that reciprocal interactions such as predator–prey, competition, and mutualism, are key drivers of community dynamics. However, there is an argument that many species interactions are asymmetric, where one species unilaterally affects another species (amensalism or commensalism). This raises the unanswered question of what is the role of unilateral interactions in community dynamics. Here I use a theoretical approach to demonstrate that unilateral interactions greatly enhance community stability. The results suggested that amensalism and commensalism were more stabilizing than symmetrical interactions, such as competition and mutualism, but they were less stabilizing than an asymmetric antagonistic interaction. A mix of unilateral interactions increased stability. Furthermore, in communities with all interaction types, unilateral interactions tended to increase stability. This study suggests that unilateral interactions play a major role in maintaining communities, underlining the need to further investigate their roles in ecosystem dynamics.

Highlights

The diversity of interaction signs is related to the asymmetry of interaction strengths
The proportion of unilateral interactions within a community is defined as pu
Extreme asymmetry leads to communities with unilateral interactions, resulting in less stability than communities with reciprocal interactions

Summary

Introduction

The diversity of interaction signs is related to the asymmetry of interaction strengths. If aij ≈aji < 0, the interaction is competition (−, −) It can be highly asymmetric and shift to amensalism (0, −) if one species is the superior competitor. If aij > 0 >aji, the interaction is antagonism (+, −) Unilateral interactions are intermediate cases when the effect of one species on another transitions from a positive effect to a negative effect and vice versa In this context, revealing the effects of unilateral interactions in community dynamics facilitates our understanding of the roles of both interaction signs and strengths that are the key elements of natural communities. Reciprocal interactions include antagonism, competition, and mutualism, whereas unilateral interactions include amensalism and commensalism. By controlling the asymmetry of interaction strengths in communities with a single interaction type and the composition of unilateral interactions within a whole community with all interaction types, I reveal the effects of unilateral interactions on community stability following May’s approach[1] (Methods)

Methods

Results

Conclusion