I think large legendaries like Kyogre, Groudon, Rayquaza, etc are at the tippy top, but normally it would be stuff like Tyranitar and Salamence(assuming of course that if Pokemon were real they would all exist in the wild *somewhere*).
An example of an area might be the route east of Fuschia. There are (as far as I recall from different games) Pidgeottos, Glooms, Oddish, Bellsprout, Weepinbel, and the occassional Venonat/moth. Pidgeotto is probably at the top here. The others get more complicated. Gloom is related to a rafflesia iirc , a rl plant that eats insects. So it preys on Venonat I suppose (moth maybe but I think it might be too large). Bellsprout, Weepinbel, same deal. Oddish is probably at the lowest tier as it is most plant like, with Venonat and Bellsprout just above it. I'm not sure what the Venos eat, but its likely they would prey on Oddish, Bellsprout and the occassional evolution thereof.
