An evolutionary stable strategy to colonize spatially extended habitats

The ability of a species to colonize newly available habitas is crucial to its overall fitness. Generally, motility and fast expansion is expected to be beneficial to the colonization process and hence to organismal fitness. Here we apply a unique evolution protocol to investigate phenotypical requirements for colonizing habitats of different sizes during range expansion of chemotaxing bacteria. Contrary to the intuitive expectation that faster is better, we show the existence of an optimal expansion speed associated with a given habitat size. Our analysis showed this effect to arise from interactions among pioneering cells at the front of the expanding population, and revealed a simple, evolutionary stable strategy for colonizing a habitat of a specific size: to expand at a speed given by the product of the growth rate and habitat size. These results illustrates stability-to-invasion as a powerful principle for the selection of phenotypes in complex ecological processes.