Gene flow and genetic drift in urban environments

Evidence is growing that human modification of landscapes has dramatically altered evolutionary processes. In urban population genetic studies, urbanization is typically predicted to act as a barrier that isolates populations of species, leading to increased genetic drift within populations and reduced gene flow between populations. However, urbanization may also facilitate dispersal among populations, leading to higher genetic diversity within and lower differentiation between urban populations. We reviewed the literature on non-adaptive urban evolution to evaluate the support for each of these urbanse urban fragmentation and facilitation models. In a review of the literature with supporting quantitative analyses of 167 published urban population genetics studies, we found a weak signature of reduced within-population genetic diversity, and no evidence of consistently increased between-population genetic differentiation associated with urbanization. In addition, we found that urban l...