Competitive exclusion and Hebbian couplings in random generalised Lotka-Volterra systems

TL;DR

This paper analyzes large ecological communities modeled by generalized Lotka-Volterra equations with random, trait-dependent interactions, identifying stability transitions and community composition changes using advanced disordered systems techniques.

Contribution

It introduces a novel analytical framework combining disordered systems theory with ecological modeling to characterize stability and community structure in complex ecosystems.

Findings

Identifies two types of stability transitions with diverging abundances.

Shows only a subset of species survives at stable fixed points.

Links dynamical transitions to spectral properties of the interaction matrix.

Abstract

We study communities emerging from generalised random Lotka--Volterra dynamics with a large number of species with interactions determined by the degree of niche overlap. Each species is endowed with a number of traits, and competition between pairs of species increases with their similarity in trait space. This leads to a model with random Hopfield-like interactions. We use tools from the theory of disordered systems, notably dynamic mean field theory, to characterise the statistics of the resulting communities at stable fixed points and determine analytically when stability breaks down. Two distinct types of transition are identified in this way, both marked by diverging abundances, but differing in the behaviour of the integrated response function. At fixed points only a fraction of the initial pool of species survives. We numerically study the eigenvalue spectra of the interaction matrix between extant species. We find evidence that the two types of dynamical transition are, respectively, associated with the bulk spectrum or an outlier eigenvalue crossing into the right half of the complex plane.