Approximately 25,000 large animals, mostly ungulates, live in the crater. Although thought of as "a natural enclosure" for a very wide variety of wildlife, 20 percent or more of the wildebeest and half the zebra populations vacate the crater in the wet season, while Cape buffalo stay; their highest numbers are during the rainy season. The crater has one of the densest known population of lions. A side effect of the crater being a natural enclosure is that the lion population is significantly inbred. This is due to the very small amount of new bloodlines that enter the local gene pool, as very few migrating male lions enter the crater from the outside. Those who do enter the crater are often prevented from contributing to the gene pool by the crater's male lions, who expel any outside competitors.