Dispersal evolution during invasions

Species' range expansions in response to climate change, and the invasion of exotic organisms, are two of the most pressing issues in ecology. Range expansions have already been documented in several taxa, including butterflies, grasshoppers and crickets, and birds, and as climate continues to change we can expect the ranges of many species to alter. Invasion of exotic organisms is of great interest currently because of the damage caused by many invasive species. Within a model, we find that during range expansion, selection generally favours individuals with a higher propensity for dispersal. This character change results in a more rapid spread than expected assuming evolutionary stasis. We show that Allee effects can slow invasion by reducing both selection for increased dispersal and chance of survival for propagules beyond the current range. Understanding how dispersal and other characters might evolve at expanding range margins is important not only for the prediction of range shifts in response to anthropogenic climate change, but also for understanding range shifting during previous natural climate change and for assessing the likely invasion dynamics of an introduced species.