Early Spatiotemporal Deficits Become Competitive Advantages During Collective Expansion

Abstract

Rapid spatial expansion into new territory is fundamental to population persistence, ecological dominance, and evolutionary success. Every race for space is initiated by founding populations, yet how their initial spatiotemporal conditions shape the outcome remains unclear. Here, by combining nonlinear theory with quantitative microbial experiments, we show that collective motility can overturn the classical logic of priority effects. Populations expanding by individual motility retain the expected advantage of an earlier start or a larger initial footprint. By contrast, under collective motility, nonlinear density-dependent feedback enables initially lagging populations to accelerate, transforming early deficits into long-term competitive advantage. Optimization predicts that this advantage is maximized when the delay scales log-linearly with initial density. We validate this scaling behavior across diverse swarming microbes, revealing a general regulatory strategy for competitive range expansion. Competition and evolution experiments further show that this behavior is adaptive and robustly preserved. Together, our results establish a quantitative framework linking the initial organization of founding populations to final spatial outcomes, helping explain how organisms regulate early dynamics to shape ecological success in space. SignificanceRapid expansion into new territory often decides who will dominate. To understand this contest, we focused on how the race begins. We built a theoretical framework linking the initial conditions of founding populations to long-run competitive outcomes, then tested its predictions experimentally in microbial populations by controlling inoculum, quantifying range expansion, competing strains head-to-head, and performing laboratory evolution. Our results show that history is not merely the starting point of range expansion, but part of the regulatory strategy for winning space. This work provides a mechanistic framework for quantitatively thinking about range expansion across systems, from microbial colonization and biological invasions to infection spread, cancer metastasis and developmental migration.