Interspecific competition slows range expansion and shapes range boundaries

Range expansion is how invasive species spread and how species track habitats shifting from climate change, so understanding this process is a key applied and basic challenge. Ecologists have long theorized that a competitor can slow or even halt range expansion. However, there has never been definitive empirical evidence of interspecific competition affecting expansion dynamics, and forecasts of spread generally do not consider competitive interactions. We demonstrate experimentally that competition between species can slow range expansion across multiple generations. We also show that competition and density-dependent dispersal continuously alter the shape of the expanding range boundary such that the shape changes over time. Therefore, accurate forecasts of range expansion must account for interactions between competing species.