# The joint influence of competition and mutualism on the biodiversity of mutualistic ecosystems

## TL;DR

This paper introduces a multilayer network framework to analyze how competition and mutualism jointly influence biodiversity in ecosystems, revealing complex interactions that affect species coexistence and ecosystem stability.

## Contribution

It develops a novel multilayer network approach that explicitly models both mutualistic and competitive interactions, moving beyond mean-field approximations in ecological network analysis.

## Key findings

- Mutualism's effect varies between specialist and generalist species.
- Biodiversity exhibits a non-trivial profile depending on competition and mutualism levels.
- Considering both interactions simultaneously alters understanding of ecosystem stability.

## Abstract

Relations among species in ecosystems can be represented by complex networks where both negative (competition) and positive (mutualism) interactions are concurrently present. Recently, it has been shown that many ecosystems can be cast into mutualistic networks, and that nestedness reduces effective inter-species competition, thus facilitating mutually beneficial interactions and increasing the number of coexisting species or the biodiversity. However, current approaches neglect the structure of inter-species competition by adopting a mean-field perspective that does not deal with competitive interactions properly. Here, we introduce a framework based on the concept of multilayer networks, which naturally accounts for both mutualism and competition. Hence, we abandon the mean field hypothesis and show, through a dynamical population model and numerical simulations, that there is an intricate relation between competition and mutualism. Specifically, we show that when all interactions are taken into account, mutualism does not have the same consequences on the evolution of specialist and generalist species. This leads to a non-trivial profile of biodiversity in the parameter space of competition and mutualism. Our findings emphasize how the simultaneous consideration of positive and negative interactions can contribute to our understanding of the delicate trade-offs between topology and biodiversity in ecosystems and call for a reconsideration of previous findings in theoretical ecology, as they may affect the structural and dynamical stability of mutualistic systems.