Natural selection is what keeps species from not over populating. It is survival of the fittest. The elk population has been going down due two the reenterduced wolves. The population of wolves went up due to the high population of elk that has now gone way down. The reason why the elk are being eaten by wolves so much is because of the wolfs hunting stratigy witch is where 3 to 7 wolves at a time attack one elk witch takes less time to kill. The other reason that wolfs play a big factor in the dicrease of elk is they mostly target young calves, cow elk, or just injured elk. They do not very often attack bulls because of there streangth and antlers witch is the elks defence. I prodicdt in the future there will be a steady elk population because there will be to many wolfs. That is where natural selection would come into play with wolves being over populated only the fittest survive.