Are zebra and wildebeests close. Zebra migrate ahead of wildebeest and eat the upper part of the grass. Wildebeest follow and crop closer to the ground. So they don't compete which is why it works so well. Therein lies the answer to your question.
Regional ecosystems work.
If they get out of balance things happen until they work again. For some reason dinosaurs ascended to dominance because things worked better that way. As always, this is only an opinion, subject to retraction and recall without notice, and with due respect to others opinions.