http://news.nationalgeographic.com/2...ors_picks=true

Wild horses grazing on the Western range, dromedary camels roaming the Australian outback, hippos lounging in Colombian lakes—they all have two things in common: They’re very large herbivores, and they’re on the “wrong” continent. They were imported from their native range by people—in the case of the hippos, by the now-deceased drug lord Pablo Escobar, whose private zoo the beasts escaped from.

THEY CAN’T GO HOME AGAIN

Many conservationists have argued that such wayward animals should be “put back” in their native habitats. But that often isn’t possible, Wallach says. The one-humped dromedary camel is an example.