An evolutionarily stable strategy to colonize spatially extended habitats.

The ability of a species to colonize newly available habitats is crucial to its overall fitness1-3 . In general, motility and fast expansion are expected to be beneficial for colonization and hence for the fitness of an organism4-7 . Here we apply an evolution protocol to investigate phenotypical requirements for colonizing habitats of different sizes during range expansion by chemotaxing bacteria8 . Contrary to the intuitive expectation that faster is better, we show that there is an optimal expansion speed for a given habitat size. Our analysis showed that this effect arises from interactions among pioneering cells at the front of the expanding population, and revealed a simple, evolutionarily stable strategy for colonizing a habitat of a specific size: to expand at a speed given by the product of the growth rate and the habitat size. These results illustrate stability-to-invasion as a powerful principle for the selection of phenotypes in complex ecological processes.