Species coexistence in a neutral dynamics with environmental noise

TL;DR

This paper investigates how environmental noise influences species coexistence in neutral ecological models, revealing that environmental variability can either decrease or enhance coexistence times depending on the fitness scaling mechanism.

Contribution

It introduces a model analyzing the impact of environmental noise on neutral species competition, highlighting the role of fitness variation and correlation time in coexistence dynamics.

Findings

Environmental fluctuations reduce coexistence time when fitness varies linearly.

Coexistence time can be increased or decreased depending on environmental correlation time.

The results are explained through the lens of Chesson's storage effect.

Abstract

Environmental fluctuations have important consequences in the organization of ecological communities, and understanding how such a variability influences the biodiversity of an ecosystem is a major question in ecology. In this paper, we analyze the case of two species competing for the resources within the framework of the neutral theory in the presence of environmental noise, devoting special attention on how such a variability modulates species fitness. The environment is dichotomous and stochastically alternates between periods favoring one of the species while disfavoring the other one, preserving neutrality on the long term. We study two different scenarios: in the first one species fitness varies linearly with the environment, and in the second one the effective fitness is re-scaled by the total fitness of the individuals competing for the same resource. We find that, in the former case environmental fluctuations always reduce the time of species coexistence, whereas such a time can be enhanced or reduced in the latter case, depending on the correlation time of the environment. This phenomenon can be understood as a direct consequence of Chesson's storage effect.