Summary based on Donlan CJ. 2007. “Restoring America’s Big, Wild Animals.” Scientific American June 2007: 72-7.
Imagine lions, elephants, and camels roaming North America. This is exactly what many well-respected conservationists are advocating for today. Long ago, species very similar to many roaming Africa and the Middle East today ruled North America. But with the European invasion and human influences on the ecosystems, very few of the large bears, camels, cats and elephants that roamed the continent back then are still around today. These megafauna had huge impacts on species interaction on our continent. Although the rewilding of North America, also known as Pleistocene rewilding, is only now coming to the public eye, the idea has been around in many forms for many years. Reintroduction of wolves into Yellowstone and Kruger National Park in Africa are two success stories.
But since most of these species are extinct, scientists suggest that proxy species be used to try to restore balance in our ecosystems. Appropriately named, it is in part because of their size that megafauna have such a disproportionately high impact on the ecosystem, and many of the species to be introduced are likely keystone animals. Much of this relies on a top-down approach: more carnivores keep herbivores in check, allowing plants to thrive which can sustain greater biodiversity.
Another benefit is similar to theories of metapopulations. Many of the species which would be introduced to North America are endangered or at risk species in their current niches. Expanding a realized niche into greater areas of the where conditions are possible for survival will create new populations, helping to ensure species survival. If stochastic events cause a decline or even extinction in one population, it could be repopulated by the population elsewhere.
Although there are obviously some major political hurdles that would have to be overcome before this would ever be a widespread practice, it is not too different from some of the most successful wild animal parks in Africa. Many worry about a Jurassic Park like scenario where animals escape and wreak havoc on communities. Others object to ideas of tampering with the "natural order." Yet for those in the know, rewilding would be a step in the right direction. Instead of merely reacting to problems, rewilding is seen as a proactive step towards maintaining and creating an ecosystem with diversity. There is nowhere on earth untouched by man, rewilding proponents argue, to pretend that this is true is false. Views of nature as pristine and untouched are too simple, if humans want to let nature thrive, we have to help it along.