Global attractors and extinction dynamics of cyclically competing species

TL;DR

This paper investigates how global attractors influence extinction and biodiversity stability in cyclically competing species, revealing phase transitions and the role of mobility and competition strength in ecological dynamics.

Contribution

It introduces a novel framework linking nonlinear attractors to extinction times and biodiversity stability in spatial ecological models.

Findings

Global attractors change qualitatively at certain mobility thresholds.

Effective free energy landscape characterizes most probable species concentrations.

Phase diagrams reveal distinct routes to extinction and biodiversity loss.

Abstract

Transitions to absorbing states are of fundamental importance in non-equilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species' concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility, and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species' global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying non-equilibrium phase transitions. We provide the complete phase diagrams for the population dynamics, and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases.