That's true, there are plenty of entries or scenes in the anime that suggest a food chain. Like Pidgeotto wanting to eat Caterpie in the beginning of the first season. And Staraptor isn't the only one listed as a predator. Several pokédex entries of Pidgeotto mention prey as well, which suggests it is a hunter too. FireRed even mentions "It can carry prey such as an Exeggcute to its nest"