• Accepted Paper

Nonlinear competition avoidance favors coexistence in spatially structured microbial populations

Mattia Mattei, David Soriano-Paños, and Alex Arenas

PRX Life - Accepted 30 September, 2026

DOI: https://doi.org/10.1103/4t9n-nvgc

Abstract

Bacteria regulate their motility through a variety of mechanisms, including quorum sensing (QS) and other density–dependent responses mediated by diffusible signals. While nonlinear densitydependent motility is well known in active-matter theory to generate nonequilibrium spatial patterns, its consequences for the coexistence of growing, interacting species remain less explored. Here we develop a minimal spatially structured model for two strongly competing species in which local demographic interactions are coupled to an escape response: each species increases its motility nonlinearly (sigmoidal) with the local abundance of its competitor. We show that this sigmoidal motility regulation promotes optimal spatial self-organization and can sustain long term coexistence via segregation, even in parameter regimes that yield competitive exclusion in well-mixed Lotka–Volterra dynamics. On two-dimensional lattices, the interplay between demographic competition and density–dependent motility generates a range of emergent patterns, including regimes in which the weaker competitor counterintuitively has higher total abundance. Overall, our results identify nonlinear, competitor–induced motility as a fundamental mechanism capable of sustaining coexistence in competing microbial populations.

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