Can different breeds of frog be kept together in a tank Are there any frogs that eat other frogs?

Yes, some frogs are specialist frog predators. As a general rule dont mix frogs that are significantly different in size. If you think that one frog could fit in the mouth of another frog, it probably will. Dont over crowd the tank either. 3-4 frogs in a three foot tank would be plenty depending upon the size of the frogs.