Re-Wilding North America

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Vol. 436|18 August 2005 COMMENTARY Re-wilding North America A plan to restore animals that disappeared 13,000 years ago from Pleistocene North America offers an alternative conservation strategy for the twenty-first century, argue Josh Donlan and colleagues.

orth America lost most of its large a over four million years in North vertebrate species — its megafauna — Large American grasslands that changed Nsome 13,000 years ago at the end of the abruptly in the Late Pleistocene; the Pleistocene. And now Africa’s large mammals now-extinct American cheetah are dying, stranded on a continent where wars (Acinonyx trumani), a key predator, are waging over scarce resources. However almost certainly shaped the prong- much we would wish otherwise, humans will required Area horn’s astonishing speed3. continue to cause extinctions, change ecosys- Small tems and alter the course of evolution. Here, PresentTime to establishment 50 years Beasts of old we outline a bold plan for preserving some of b Although historical perspectives our global megafaunal heritage — one that High have influenced modern conser- aims to restore some of the evolutionary and vation planning, existing pro- ecological potential that was lost 13,000 years grammes do not adequately ago, and which offers an alternative vision for address the evolutionary potential twenty-first century conservation biology. and long-term processes involved Our vision begins immediately, spans the in restoring large-mammal diver-

coming century, and is justified on ecological, value Conservation sity. Africa and parts of Asia are Low Low High evolutionary, economic, aesthetic and ethical Ecological rate / ecosystem interactivity now the only places where grounds. The idea is to actively promote the megafauna are relatively intact, restoration of large wild vertebrates into North c and the loss of many of these America in preference to the ‘pests and weeds’ High species within this century seems (rats and dandelions) that will otherwise come likely. Given this risk of further to dominate the landscape. This ‘Pleistocene extinction, re-wilding of North re-wilding’ would be achieved through a series American sites carries global con- of carefully managed ecosystem manipula- servation implications. tions using closely related species as proxies for value cultural Moreover, humans have emo- extinct large vertebrates, and would change the economic/ Potential tional relationships with large Low Low High underlying premise of conservation biology Potential economic / cultural conflict vertebrates that reflect our own from managing extinction to actively restoring Pleistocene heritage. More than 1.5 natural processes. Figure 1 | Pleistocene re-wilding in North America. Symbols million people annually visit San represent horses (Equus caballus and E. asinus in black; Diego’s Wild Animal Park to catch Historic vision E. przewalskii and E. hemionus in grey), Bolson tortoises, a glimpse of large mammals — Our proposal is based on several observations. camelids, cheetahs, Asian (grey) and African (black) elephants, more than the number of visitors First, Earth is nowhere pristine; our econom- and lions. a, The likely timescale and area required to restore to most US National Parks. So an proxies for extinct large vertebrates. b, Conservation value and ics, politics, demographics and technology understanding of ecological and ecological role (interactivity with other species) on the landscape. pervade every ecosystem. Such human influ- c, Potential economic/cultural value versus potential conflict. evolutionary history, inspired by ences are unprecedented and show alarming visits to private or public reserves signs of worsening. Second, environmentalists restoration benchmark. But the arrival of the containing free-roaming megafauna, could are easily caricatured as purveyors of doom first Americans from Eurasia roughly 13,000 strengthen support for conservation. Pleisto- and gloom, to the detriment of conservation. years ago constitutes a less arbitrary baseline. cene re-wilding would probably increase the Third, although human land-use patterns are Mammal body-size distributions were similar appeal and economic value of both private and dynamic and uncertain, in some areas, such as across all continents before the Late Pleis- public reserves, as evidenced by the restoration parts of the Great Plains in the United States, tocene, but subsequent extinction of most of wolves to Yellowstone National Park4. human populations are declining1 — which large species drastically altered those distribu- We foresee several phases to Pleistocene re- may offer future conservation opportunities. tions in favour of smaller species. wilding, some of which are already under way. Fourth, humans were probably at least partly In the Americas, where large-vertebrate The 50-kg Bolson tortoise (Gopherus flavo- responsible for the Late Pleistocene extinc- losses were greatest, the subsequent changes marginatus) was widely distributed across the tions in North America, and our subsequent were undoubtedly ecologically and evolution- Chihuahuan desert until the Late Pleistocene. activities have curtailed the evolutionary arily significant. Large carnivores and herbi- Today it survives only in a small part of north- potential of most remaining large vertebrates. vores often play important roles in the ern Mexico and is critically endangered. A We therefore bear an ethical responsibility to maintenance of biodiversity, and thus many number of appropriate sites exist for re- redress these problems. extinct mammals must have shaped the evolu- introduction, including Big Bend National North American conservationists routinely tion of the species we know today2. For example, Park, Texas. And repatriation of captive Bol- turn to the arrival of Columbus in 1492 as a the pronghorn (Antilocapra americana) evolved son tortoises to a private ranch in New Mexico

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COMMENTARY NATURE|Vol 436|18 August 2005

is currently under study. Restoring North ing African and Asian elephants are in grave vores, while surrounding towns would benefit America’s largest surviving temperate terrestrial danger. Elephants inhibit woodland regenera- economically from management and tourism- reptile to its prehistoric range could bring eco- tion and promote grasslands, as Pleistocene related jobs. A system of similar reserves across logical, evolutionary, economic and cultural proboscidians probably once did. With appro- several continents offers the best hope for long- benefits, with no apparent costs (Fig. 1). priate resources, captive US stock and some of term survival of large mammals. Likewise, horses and camels originated in the 16,000 domesticated elephants in Asia could North America, and many species were present be introduced to North America, where they Meeting the challenge in the Late Pleistocene. Feral horses (Equus might suppress the woody plants that threaten In the coming century, by default or design, caballus) and asses (E. asinus), widely viewed as western grasslands. Fencing, which can be we will constrain the breadth and future evo- pests in the United States, are plausible proxies effective in reducing human–elephant conflict lutionary complexity of life on Earth. The for extinct American species. Also, given that in Africa, would be the main economic cost. default scenario will surely include ever more most of the surviving Eurasian and African Lions, which play a pivotal ecological role in pest-and-weed dominated landscapes, the species are now critically endangered, estab- the Serengeti, represent the ultimate in Pleis- extinction of most, if not all, large vertebrates, lishing Asian asses (E. hemionus) and Przewal- tocene re-wilding for North America. They are and a continuing struggle to slow the loss of ski’s horse (E. przewalskii) in North America increasingly threatened, with populations in biodiversity. might help prevent the extinction of these Asia and some parts of Africa critically endan- Pleistocene re-wilding is an optimistic alter- endangered species and would restore equid gered. Replacing the extinct American lion native. We ask of those who find the objections species to their evolutionary homeland. (Panthera leo atrox), although challenging, has compelling, are you content with the negative Similarly, Bactrian camels clear aesthetic and economic slant of current conservation philosophy? Will (Camelus bactrianus) in “Re-wilding of North benefits (Fig. 1). you settle for an American wilderness emptier North America could provide American sites carries Among the objections to than it was just 100 centuries ago? Will you risk a modern proxy for Camelops, Pleistocene re-wilding is that the extinction of the world’s megafauna should a late Pleistocene camelid. global conservation the proposed proxies are not economic, political and climate change prove Wild Bactrian camels are on implications.” genetically identical to the catastrophic for those populations remaining the verge of extinction, cur- animals that formerly existed in Asia and Africa? The obstacles are substan- rently restricted to the Gobi desert. Domesti- in North America. And our vision might strike tial and the risks are not trivial, but we can no cated or captive camels might benefit arid some as ‘playing God’. Existing lions and chee- longer accept a hands-off approach to wilder- North American ecosystems by browsing on tahs are somewhat smaller than their extinct ness preservation. Instead, we want to reinvig- woody plants that today often dominate counterparts, for example, and Camelus is dif- orate wild places, as widely and rapidly as is southwestern US landscapes. With proper ferent from Camelops. ‘Same’ is relative, how- prudently possible. ■ management, camels could provide economic ever, as illustrated by the highly successful Josh Donlan is in the Department of Ecology and benefits as well5. The overall benefits and dis- reintroduction of peregrine falcons (Falco Evolutionary Biology, Cornell University, Ithaca, advantages of horses and camels as proxies will peregrinus) in North America. Captive-bred New York, New York 14853, USA. depend on local contexts, and possibly on the birds from seven subspecies on four conti- Co-authors are Harry W. Greene of Cornell presence of appropriate predators. nents were used, yet there were no differences University; Joel Berger who is at the Teton Field among the birds in subsequent breeding Office, Wildlife Conservation Society; Carl E. Free to roam success6, and the subspecies now serve as a Bock and Jane H. Bock of the University of The second, more controversial phase of Pleis- collective proxy for the extinct midwestern Colorado, Boulder; David A. Burney of Fordham tocene re-wilding could also begin immediately, peregrine falcon. University, New York; James A. Estes of the US with the maintenance of small numbers of More challenging objections to Pleistocene Geological Survey, University of California, Santa African cheetahs (Acinonyx jubatus), Asian re-wilding include the possibility of disease Cruz; Dave Foreman of the Re-wilding Institute, (Elephas maximus) and African (Loxodonta transmission, the fact that habitats have not Albuquerque, New Mexico; Paul S. Martin of the africana) elephants, and lions (Panthera leo) on remained static over millennia, and the likeli- Department of Geosciences, University of private property. Many of these animals are hood of unexpected ecological and social Arizona, Tucson; Gary W. Roemer of the already in captivity in the United States, and the consequences of reintroductions. These issues Department of Fishery and Wildlife Sciences, primary challenge will be to provide them with must be addressed by sound research, prescient New Mexico State University, Las Cruces, New naturalistic settings, including large protected management plans and unbiased public dis- Mexico; Felisa A. Smith of the University of New areas of appropriate habitat and, in the case of course on a case-by-case and locality-by-local- Mexico, Albuquerque; and Michael E. Soulé who carnivores, live prey. ity basis. Well-designed, hypothesis-driven is based at Hotchkiss, Colorado. The African cheetah, a close relative of the experiments will be needed to assess the 1. Lonsdale, R. E. & Archer, J. C. J. Geogr. 97, 108–122 (1998). American cheetah, has only a modest chance impacts of potential introductions before 2. Janzen, D. H. & Martin, P. S. Science 215, 19–27 (1982). of persisting in the wild in the next century. releases take place. Large tracts of private land 3. Byers, J. A. American Pronghorn: Social Adaptations and the Breeding programmes are not self-sustaining, probably hold the best immediate potential for Ghosts of Predators Past (Chicago Univ., Chicago, 1997). 4. Duffield, W. J. & Neher, C. J. Economics of Wolf Recovery in but some of the 1,000 captive animals could be such studies, with the fossil record and research Yellowstone National Park. Transactions of the 61st North used in re-wilding. Free-roaming, managed providing guideposts and safeguards. For American Wildlife and Natural Resources Conference cheetahs in the southwestern United States example, 77,000 large mammals (most of them 285–292 (Wild Mgmt. Inst., Washington DC, 1996). 5. Phillips, A., Heucke, J., Dorgers, B. & O'Reilly, G. Co-grazing could save the fastest carnivore from extinc- Asian and African ungulates, but also cheetahs, Cattle and Camels. A report for the Rural Industries Research tion, restore what must have been strong camels and kangaroos) roam free on Texas and Development Corporation (Rural Industries Research interactions with pronghorn, and facilitate ranches7, although their significance for con- and Development Corporation, Kingston, 2001). ecotourism as an economic alternative for servation remains largely unevaluated. 6. Tordoff, H. B. & Redig, P. T. Conserv. Biol. 15, 528–532 (2001). ranchers (Fig. 1). The third stage in our vision for Pleistocene 7. Schmidly, D. J. Texas Natural History: A Century of Change Managed elephant populations could simi- re-wilding would entail one or more ‘ecological (Texas Tech Univ. Press, Lubbock, 2002). larly benefit ranchers through grassland main- history parks’, covering vast areas of economi- tenance and ecotourism (Fig. 1). Five species of cally depressed parts of the Great Plains. As is Acknowledgements: We thank the Environmental Leadership Program, Lichen Foundation, Turner Endangered proboscidians (mammoths, mastadons and the case today in Africa, perimeter fencing Species Fund, New Mexico Agricultural Station, Ladder gomphotheres) once roamed North America in would limit the movements of otherwise free- Ranch, C. Buell., S. Dobrott, T. Gorton, M. K. Phillips and the Late Pleistocene; today many of the remain- living ungulates, elephants and large carni- J. C. Truett for support and encouragement.