Another question which I think is related to this thread...
Where are traditional animals in the Pokemon world? Would people eat Pokemon?
I get the impression that traditional animals don't exist in Pokemon, but that Pokemon are the animals, the only form of wildlife they have.
EDIT: after looking it up, traditional animals are mentioned/shown in pokemon. However I think this is a strange subject, because so many pokemon are similar to regular animals. I think for the most part pokemon are the animals, and when the pokedex says "a mouse like creature" it is for the benefit of the game player, not because those animals are common in pokemon land.
I mean regular animals wouldnt stand a chance in their habitat with lighting shooting firebreathing creatures roaming around.