Why might urbanization infl uence plant evolution? Clearly, urban development changes both the biotic and abiotic environment in ways that could alter natural selection and adaptive evolution within plant populations. Urbanization may also infl uence nonadaptive evolution due to altered gene fl ow, genetic drift, or nonrandom mating. For example, urban development causes habitat fragmentation given that buildings and roads are a common feature to every city, where extensive pavement, concrete, and alteration of natural habitats is the rule rather than the exception. Th is fragmentation can limit dispersal and gene fl ow, leading to greater genetic diff erentiation between populations. It can also infl uence the size of populations and thus the importance of neutral evolution because genetic drift will be greater in smaller populations. Finally, urban areas can alter mating patterns (e.g., increased selfing) through changes in pollinator communities...
The authors then make several predictions:
- Urban and non-urban populations will diff er in the amount of genetic diversity
- Urbanization will alter natural selection on populations
- Neutral evolution will be greater in urban areas
- Genetic divergence between urban and non-urban populations will be proportional to the size of urban areas
- Insect-pollinated plants will evolve greater selfpollination or clonal growth in urban areas
Thus the five predictions above I believe are at most a small part of the complexity of urban development. For example I have more than twice the tree species on my small acreage than indigenous plants would provide. Some of the trees are quite hardy and aggressive such as Ginkgo and Metasequoia.
I believe that a more details analysis and monitoring would be quite useful, and that what the authors propose may be quite limited.