Neutral species facilitate coexistence among cyclically competing species under birth and death processes

TL;DR

This study investigates how neutral species influence biodiversity in cyclically competing populations under birth and death processes, revealing their dual role in either promoting or reducing biodiversity depending on their interference.

Contribution

It introduces a spatial RPS model with neutral species and birth-death dynamics, highlighting their complex effects on biodiversity and ecosystem stability.

Findings

Neutral species can dominate space when interference is positive.

Harmful interference increases densities of competing species.

Biodiversity is maintained even at high mobility regimes.

Abstract

Natural birth and death are fundamental mechanisms of population dynamics in ecosystems and have played pivotal roles in shaping population dynamics. Nevertheless, in studies of cyclic competition systems governed by the rock-paper-scissors (RPS) game, these mechanisms have often been ignored in analyses of biodiversity. On the other hand, given the prevalence and profound impact on biodiversity, understanding how higher-order interactions (HOIs) can affect biodiversity is one of the most challenging issues, and thus HOIs have been continuously studied for their effects on biodiversity in systems of cyclic competing populations, with a focus on neutral species. However, in real ecosystems, species can evolve and die naturally or be preyed upon by predators, whereas previous studies have considered only classic reaction rules among three species with a neutral, nonparticipant species. To identify how neutral species can affect the biodiversity of the RPS system when species' natural birth and death are assumed, we consider a model of neutral species in higher-order interactions within the spatial RPS system, assuming birth-and-death processes. Extensive simulations show that when neutral species interfere positively, they dominate the available space, thereby reducing the proportion of other species. Conversely, when the interference is harmful, the density of competing species increases. In addition, unlike traditional RPS dynamics, biodiversity can be effectively maintained even in high-mobility regimes. Our study reaffirms the critical role of neutral species in preserving biodiversity.