In our typical fantasy worlds, we have a lot of monsters. People like their monsters. One problem with the plethora of monsters we usually see in D&D and similar games is that they tend to be all carnivores. Carnivores are scary. In general, herbivores are less scary... with some notable exceptions (hippopotamus, I'm looking at you... and backing away).
Of course, carnivores typically eat herbivores. If we're going to have a world full of large carnivores and we care about verisimilitude at all (which you may not, but many do), then we need things for them to eat. What would they eat? Largish herbivores would be good. Something that breeds like bunnies would be... Hey! How about:
The material enclosed in the box below is released via the Open Game License.
I figure it is a good start.