|MadSci Network: Genetics|
The context of your quote comes from an online forum. Apparently the writer is objecting to a hypothetical argument about how dogs could eventually speciate if populations of wolves and chihuahuas were isolated somewhere. What he or she means by "bandwidth" is apparently "genetic diversity".
First of all, wolves aren't considered the same species as domestic dogs to begin with, although they can interbreed under some circumstances. The main issue here, I suppose, is whether many species actually have sufficient genetic diversity to allow for speciation to occur. Dogs have been artificially selected for a wide range of diversity, so they're probably at the high end of the diversity scale. Cheetahs have gone through a population bottleneck in the past, so that the existing wild cheetahs are all descended fairly recently from a very small group of individuals. This means that cheetahs are all very closely related, so much so that random individuals will accept skin grafts from each other. The unusual paucity of genetic variation in cheetahs is briefly reviewed in an article by Stephen O'Brien that is available full text online (O'Brien, 1994).
So, domestic dogs are probably not a good example to use for population genetics, because of their manipulation by humans; cheetahs would also be a poor example, because they're unusually inbred. A typical species would have quite a lot of genetic variation or "bandwidth", and furthermore, new diversity continually arises by mutation. It doesn't appear that lack of variation is usually a limiting factor in formation of new species. There are numerous known examples of speciation actually being observed, both in the wild and in the lab, so this isn't a hypothetical question in the first place. A nicely documented discussion of observed speciation is available at the TalkOrigins site .
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