Introducing lions, cheetahs, elephants, camels and other large non-indigenous animals to the U.S. Great Plains and Southwest -- a plan proposed in the journal Nature last year -- wouldn't work, several Cornell researchers argue. Such animals would be unlikely to thrive and could seriously threaten indigenous species and ecosystems, they say.
The original proposal, called Pleistocene rewilding and published by another group of researchers from Cornell and other institutions, suggested introducing close relatives or ecological counterparts to such species as mammoths, saber-toothed tigers and North American cheetahs, which roamed the North American plains during the Pleistocene era but were driven to extinction 10,000 years ago by humans. Introducing related species could fill vacant niches and revitalize ecosystems that have suffered from the extinctions, the researchers proposed.
The proposal's challengers, who recently published their paper in Biological Conservation, argue that plants that support the food web in the Great Plains region and the Southwest have evolved and changed irrevocably over the past 10,000 years without the large herbivores and predators that once influenced these ecosystems. Adding exotic proxy species now would not restore the gaps from 10,000 years ago.
"We can never return North American ecosystems to the way that they were in the Pleistocene, especially since we are not sure what they really were like back then," said Dustin Rubenstein, the paper's lead author and a graduate student in Cornell's Department of Neurobiology and Behavior. "The goal now should be to preserve and maintain what native ecosystems and organisms are left."
Further, the authors argue, modern lions, elephants, cheetahs and camels have never lived in these areas and serve as poor proxy species for extinct native Pleistocene animals. Moreover, relocated large mammals are unlikely to flourish and, even worse, could jeopardize indigenous species and ecosystems rather than restore the biodiversity and health of these natural areas.
Resources would be better spent, the authors argue, protecting threatened indigenous species and reintroducing them to areas within their historic ranges from which they went locally extinct, the way that wolves were reintroduced to Yellowstone National Park.
The original rewilding proposal in Nature noted that research shows that top predators play important roles in structuring ecosystems and maintaining biodiversity. For example, when humans wiped out wolves and grizzlies, elk populations soared, willows were nibbled away, and beavers (for whom willows are a favorite meal) suffered huge losses in some areas.
The scientifically based Pleistocene rewilding plan also offered a new way to save large animals struggling with habitat loss elsewhere, according to the paper.
While one aim of Pleistocene rewilding is to galvanize support for conservation, relocating exotic Asian and African animals could divert attention away from conservation efforts in cash-poor but biologically rich developing nations, Rubinstein and his co-authors argue. Furthermore, incidents of farmers battling crop destruction from herds of elephants or attacks on cattle or people by lions or cheetahs could lead to an anti-conservation backlash in the United States.
Nevertheless, they note that "rewilding," or reintroducing captive or wild-bred species that have gone locally extinct in the past few hundred years, is a common and effective practice, because neither the target species nor its habitats have had time to change very much genetically. But, they say, Pleistocene rewilding is completely different as it introduces exotic large animals to ecosystems that have evolved without them for millennia.
Nonetheless, "It is great that people are considering Pleistocene rewilding," said co-author Paul Sherman, Cornell professor of neurobiology and behavior. "While there is considerable disagreement over its merits, it is an innovative idea that should be discussed by both scientific and popular audiences. Our paper is a contribution to the former."
The original researchers, who include former Cornell graduate student and first author Josh Donlan and Cornell conservation biologist Harry Greene, will publish an in-depth defense of their Pleistocene rewilding in the August issue of The American Naturalist.