Well in the games, some Pokedex entries have already stated that Pokemon do prey on other species of Pokemon. One example I could think of would be Heatmor and Durant.
Same goes for Taillow/Swellow and Wurmple.
Oh and I'm pretty sure the same goes for the manga too:
Yeeep, that was a wild Carnivine trying to eat a Munchlax and a Chatot.
The same could definitely be said for the anime. Pidgeotto attempted to peck at Ash's Caterpie, and Meowth tried to eat a Magikarp once.