Some ecologists are proposing relocating large mammals that are endangered on other continents to create new herds on the North American Great Plains:
Lions stalking deer in the stubble of a Nebraska corn field. Elephants trumpeting across Colorado's high plains. Cheetah slouching through the West Texas scrub. Prominent ecologists are floating an audacious plan that sounds like a "Jumanji" sequel _ transplant African wildlife to the Great Plains of North America....Part of the justification for this transplantation is that North America once had large mammals whose ecological roles could be replicated by African mammals. At the end of the last Ice Age, the plains were populated by mastodons and saber-toothed cats, among others. Yet if the point of the exercise is returning the Great Plains to its condition at some point in the past, a better approach would be to reintroduce or support the large mammals that are native to this continent - wolves, deer, bison, etc. We have a much better sense of how these native creatures functioned in their ecosystem and in what proportions they existed than we do for the extinct mammals that roamed North America tens of thousands of years ago.
The authors contend it could help save Africa's poster species from extinction, where protection is spotty and habitat is vanishing.
They also believe the relocated animals could restore biodiversity on this continent to a condition closer to what nature was like before humans overran the landscape.
We also do not know what harmful effects introduction of large mammals would have. Some ranchers in the plains have already expressed concern for their livestock and agricultural fields. Native wild animal populations would almost certainly feel the impact as well. We know from the introduction of the European starling and house sparrow that new species can wreak havoc in their new ecosystem by pushing native species out of niches they might otherwise occupy. The spread of new diseases - such as the West Nile Virus from Africa or the strains of bird flu from Asia - should also be a cause for restraint when it comes to moving animals around. Any substantial population is going to carry its own diseases along with it; even if these do not jump to humans they very well might jump to native species. We learned this lesson once in the Americas; I do not think we need to try it again.
I hope this does not go beyond speculation.