Range expansion during recolonization: what does animal personality have to do with it?

At the edge of an ongoing expansion, pioneer individuals encounter novel ecological and evolutionary pressures that may not be experienced by conspecifics settled in long-colonized areas. Consistent behavioral differences among conspecifics (animal personality) may be important determinants of individuals' successful colonization of novel environments and range expansion. By enhancing an individual's ability to find food and shelter as well as increasing its capacity to navigate novel environments, behavioral traits such as exploration and risk-taking are thus expected to be more highly expressed in populations undergoing expansion than in established populations. We investigated among-individual variation in behaviors associated to risk-taking and exploratory tendencies in populations of small mammals during different stages of the colonization process. Using a standardized behavioral test in the field, we quantified exploration and boldness of striped field mice (Apodemus agrarius, N = 95) from six subpopulations from Germany, where they are established, and in Slovakia, where a recolonization of the area is currently in progress, and in control species bank voles (Myodes glareolus, N = 76) that shared the same habitats but were long-established at all sites. Striped field mice in the expanding populations were significantly slower in exploring the open field arena, while showing comparable levels of risk taking compared to conspecifics from established populations. No difference in behavior was detected between the populations of bank voles. Our results suggest that a slow exploration strategy might play an advantageous role in expansion processes of small mammal populations.