|MadSci Network: Zoology|
Lucy, I'm afraid I am not Dr Susman, but I will do my best ! Urban foxes certainly look different from 'wild' ones, although it is worth remembering that all land in this overcrowded country is managed to some extent, so it is questionable whether there are any genuinely 'wild' animals ! I think they look different because they are living in a very different environment from the wild ones. Urban foxes often live at much higher densities than is natural, resulting in raised levels of stress from many factors, especially increased levels of disease and parasites. Certainly, populations of animals living in different environments are subjected to different selective pressures, and will diverge genetically until they become separate subspecies, or even species. However, each city has its own population of foxes, so each might become a separate subspecies. This is unlikely because the populations are small and unstable, for instance the population of foxes in Bristol became virtually extinct after reaching a very high density, due to an epidemic of mange. In this event, the population will probably be replaced by foxes from outside the city, and any genetic uniqueness will be lost. Even if the fox population of a city does not crash, there will be continuous gene flow across the boundary between urban and wild foxes, preventing the isolation of a genetically unique sub-population. So - to answer your question, yes, I do think the environmental differences between the inside and outside of a city are great enough to drive evolutionary change, but I don't think it will happen because populations of city foxes are too small and unstable. I looked up the taxonomy of foxes in Corbet & Harris - The Handbook of British Mammals, 3rd edition, and it has been suggested that Scottish foxes should be a separate subspecies because they are larger than English ones. This suggestion was rejected (I'm not sure who by !) and they go on to discuss whether British foxes should be a different subspecies from European, or a different species from N American - etc. Basically, if you compare any two populations of animals, you will find differences. Home counties humans are an obvious case in point, but the question is - at what point do the differences become great enough to justify creation of a subspecies ? The answer, as with that old chestnut 'What is a species ?' is 'What a good taxonomist says it is'.