Speciation Through the Lens of Population Dynamics: A Theoretical Primer on How Small and Large Populations Diverge

ABSTRACT Speciation—the process by which new species arise—is fundamentally influenced by population‐level factors, such as population size and demographic dynamics. Here, we review how population size and its dynamics shape speciation mechanisms and the generation of biodiversity across evolutionary scales. Small populations can undergo rapid genetic changes via drift and founder events, potentially promoting speciation, whereas large populations harbor greater genetic diversity and adaptive potential, influencing divergence in different ways. We examine how genetic drift and gene flow interact to facilitate or impede speciation under various scenarios and how extinction risk during adaptation affects the development of reproductive isolation. Finally, we explore how speciation rates and the persistence of populations/species over time are related in theoretical models. We highlight insights from mathematical models—especially those explicitly incorporating population size—and identify open questions for future research.