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Focus: Brave New World REWILDING NORTH AMERICA One elephant at a time By Alexandra Mushegian G round sloths occupy a small but beloved role in the collective imagination. These five-ton, seventeenfoot hamster-like herbivores, which went extinct somewhere around 10,000 years ago, are commonly found as skeletons posing in natural history museums. Populations of these animals were thriving in North America when humans first arrived over the Bering Land Bridge along with mammoths, lions, saber-toothed cats, twenty-pound beavers, and several species of giant tortoise, not to mention a multitude of deer and ox-like species. Shortly after humans arrived, they all died out. The Pleistocene epoch, which ended 10,000 years ago (in archaeological terms, the end of the Paleolithic), was a golden age of animal exoticism worldwide. Why it ended—why this geological period saw a series of massive global collapses of large animal biodiversity— is a contentious topic. Many argue that the primary reason was climate change in the form of global deglaciation. Increasingly, though, studies are suggesting that it was human activity, in the form of hunting, habitat alteration, and the introduction of new diseases, that was the major cause of these extinctions. Without exception, the timing of major biodiversity reductions on all continents and large islands coincides with the arrival of early humans, with many species dying out within a few hundred years after humans arrived (1). The only continents still possessing noteworthy megafaunal diversity— Africa, and to a lesser extent, Asia—are the continents where humans coevolved with animals for the longest time. Now, due to political and socioeconomic instability in those regions, they are in danger there too. Some scientists believe that the loss of large vertebrate biodiversity has graver consequences than merely a reduction in worldwide biodiversity. Ecological studies suggest that large herbivores and predators are crucial to maintaining healthy, robust ecosystems. Some see the loss of these species as one that will have perilous future consequences. In response, they’ve come up with a controversial plan: they want to bring them back to the USA. 14 Harvard Science Review • fall 2008 rewilding-2.indd 14 2/9/2009 11:29:34 PM Focus: Brave New World group dedicated to rescuing fish habitats such as mangroves and salt marshes. But the radicalism of the Pleistocene rewilding concept lies in the scale of the project in both time and space. Proponents of this plan want to restore ecosystems that existed 13,000 years ago, and they want to revert to wilderness areas of thousands of square miles. Stipulating carefully planned, progressive ecological studies and small-scaled experiments, Pleistocene rewilding would see the introduction of giant tortoises, horses, camelids (llamas), and most unexpectedly, lions, cheetahs, and elephants to the American Southwest and Great Plains regions. All of these species had close relatives living in North America during the Pleistocene (the Asian elephant, for example, is more closely related to the woolly mammoth than it is to the African elephant) (4). These species would be set loose to pursue their normal predator-prey interactions to reshape the American environment. This plan would represent a shift in conservation practice from focusing on cataloging and slowing biodiversity loss to actively managing and promoting “Stipulating carefully planned, progressive ecological studies and small-scaled experiments, Pleistocene rewilding would see the introduction of giant tortoises, horses, camelids (llamas), and most unexpectedly, lions, cheetahs, and elephants to the American Southwest and Great Plains regions.” Mammoths are one of the groups of animals that lived on the North American landmass before becoming extinct. credit: Gianni Dagli Orti/Corbis Science Vol 319. 7 March 2008 p. 1331 Pleistocene Rewilding In 2005, a group of scientists published a two-page proposal in Nature. This short paper had enormous scope and ambition. In response to what they saw as the takeover of North America by “dandelions and rats,” Josh Donlan and his colleagues proposed that a viable solution might be to use African and Asian species as analogues of extinct Pleistocene North American species, introducing them to areas of North America set aside to become the wilderness again. If done right, they claimed, this method would restore North American ecological health and save species from extinction (2). Ecological restoration projects are undertaken all the time. Peregrine falcons, for example, were on the brink of extinction from DDT contamination before a program bred together several subspecies from both the New and Old Worlds and reintroduced them into the wild. Peregrines have proven to be adaptable and appear to be thriving (3). Many conservation agencies strive to restore endangered habitats, such as the National Oceanic and Atmospheric Administration’s Restoration Center, a fall 2008 • Harvard Science Review 15 rewilding-2.indd 15 2/9/2009 11:29:34 PM Focus: Brave New World The diagram to the left maps the correlation between human arrival and extinction of indigenous species, as well as the strength of that evidence. productive, diverse ecosystems. credit:Science Volume 306 . 1 October 2004 The Plan Pleistocene rewilding would start with small-scale ecological studies of the way exotic species respond to being repatriated to North American environments. These studies would start with less dramatic species—tortoises, llamas—and would progress to more challenging species like big cats. Many species, such as cheetahs, already exist in captivity in the US; they would be placed on large private properties with potential prey and the predator-prey interactions and dynamics over time would be carefully studied by experts on the species (5). In addition, information about the flora of the Pleistocene could be reconstructed from pollen in the fossil record. Once there is a significant body of research, the next step would be to find huge tracts of land to be rewilded. The authors of the paper suggest economically depressed regions of the Great Plains as good candidates for such an endeavor. The area would be securely fenced and given the status of a national park or nature preserve. Hopefully, it would become a tourist attraction that would bring economic benefits to the surrounding region. Similar plans are already being attempted in at least two spots in the world: Oostvaardersplassen, a nature reserve in the Netherlands focusing on restoration of large ungulates, and Lenskiye Stolby, Siberia, commonly known as “Pleistocene Park.” (6). The Benefits of Rewilding Why exactly are large vertebrates so important? Various studies show that predators, as well as some of the more impressive herbivores, play a disproportionately large role in maintaining “ecological function.” “Ecological function” means, roughly, an ecosystem’s ability to rebound from shocks, adapt to changing conditions, and evolve to greater and greater fitness—in other words, general vitality. Predators help control herbivore populations, keeping them from over-expanding, destroying all vegetation, and subsequently starving. The importance of this “topdown” control effect has been confirmed in many situations. Plant biomass declined by 40% in parts of the Arctic tundra from which predators were excluded (7). Closer to home, many areas of the United States are facing problems because out-of-control deer populations are decimating forests and living perpetually half-starved and disease-ridden (and also carrying Lyme disease, a debilitating illness that is spread from deer to humans by ticks) (8). Deers’ previous predators, wolves and mountain lions, are largely absent in the wild because they were hunted as dangers by humans, and because their forest habitats are too fragmented to allow them to have the large areas they need to thrive. A recent review of multiple studies from Venezuelan terrestrial and various marine ecosystems concludes that “we live in a largely topdown regulated world” (9). Large herbivores, too, contribute to ecosystem diversity, usually by virtue 16 Harvard Science Review • fall 2008 rewilding-2.indd 16 2/9/2009 11:29:34 PM Focus: Brave New World of their very size and gawkiness—for example, elephants trample vegetation and tortoises dig long burrows. These sorts of activities create heterogeneity in the environment, opening up a variety of ecological niches than can then be filled by different plant and animal species. The more diverse and varied a landscape is, the greater its robustness and adaptability. By feeding on shrubs and saplings, elephants maintain grassland ecosystems; camelids feed on the type of weedy, scrubby species that otherwise threaten to take over landscapes. In the Siberian “Pleistocene Park,” current studies are exploring the effects of tundra wildlife on global warming. Potentially, the activity of large mammals may disturb snow cover enough to keep the soil continually exposed to the cold, preventing permafrost from melting and reducing the release of additional CO2 from the soil (10). North America today, with the disappearance of bison and the domination of industrial-scale agricultural monocultures, is “impoverished,” according to Harry Greene, a professor at Cornell and one of the co-authors of the original proposal (5). Ecologically, he says, “we can likely do better” (5). The possibility of partially restoring the lost ecological and evolutionary potential of North American landscapes, he said in an email interview, was in his opinion the single best argument for Pleistocene rewilding (5). The Objections to Rewilding A natural initial objection to the Pleistocene rewilding proposal is pure incredulity—elephants? Here? Once one has heard the justification for the proposal, concerns still remain about viability and potential consequences. One objection is that too much time has passed since the Pleistocene for the concept of ecologically analogous species to be valid. Both the species and the environment have undoubtedly changed significantly since those times and thus the introduction of exotic species to a different continent could have ecologically harmful effects due to unforeseen interactions with the current natives. Furthermore, introduced species could carry latent pathogens that might thrive in a new setting, bringing diseases that might threaten both nature and agriculture. Even if there are not dramatically deleterious effects, the desired outcome of increasing ecological function might simply not happe, if assumptions about species interactions and ecological roles turned out to be wrong (12). Extensive research is certainly necessary to evaluate the threat of these sorts of problems. Obviously, there are economic considerations as well. The research leading up to and during Pleistocene rewilding efforts must be funded, as well as the allocation of land, the installation of fences around Pleistocene wilderness areas, and the hiring of managers to monitor the borders. The occasional escape would be inevitable and elephants or lions on the loose would create a terribly dangerous situation. . “Cost might be a big deal, possibly insurmountable,” Greene said. “But in terms of if money were not an issue, I think what really bugs people, including fellow biologists, is not ‘exotics’ and so forth, but rather [the idea of] bringing back something that can kill us” (5). The existence of Pleistocene wilderness reserves would force people to adjust their attitudes about the other animals that share their landscape and return a concern that North Americans have largely not had to face for a long time. Indirect economic consequences and ethical problems will arise when the question of where to get the animals from is decided—currently, trade in exotic species is largely prohibited and negotiating with countries to acquire their animals is likely to be complicated. Along similar lines, there are fears that North American Pleistocene rewilding will divert attention and resources from conservation within Africa and Asia (11). Questions to Ponder The debate about Pleistocene rewilding raises deep and important questions about humans’ role in the biosphere. Are we responsible for atoning for the destructiveness of our thirteen thousand year old ancestors? Are we a species like any other, our capacity for destruction just part of our evolutionary advantage? Or is it now our role to serve as large-scale gardeners, making sure the world thrives? What does it mean when we influence the course of evolution? As the idea of Pleistocene rewilding gains attention, we will have to take a look at just how well we know the species with which we share the planet. —Alexandra A. Mushegian ’10 is an Organismic and Evolutionary Biology concentrator in Currier House. References 1. Burney DA and Flannery TF, “Fifty millenia of catastrophic exinction after human contact” (2005). Trends in Ecology and Evolution 20:7. 2. Donlan CJ et al, “Re-wilding North America” (2005). Nature 436:18. 3. Tordoff HB and Redig PT, “Role of genetic background in the success of reintroduced peregrine falcons” (2001). Conservation Biology 15:2. 4. Donlan CJ et al, “Pleistocene Rewilding: An optimistic agenda for twenty-first century conservation” (2006). The American Naturalist 168:5. 5. Greene, Harry. Personal correspondence, October 2008. 6. Curry, Andrew, “Pleistocene Park: Where the auroxen roam” (2008). Wired magazine, 22September 2008, accessed online October 2008 at http://www. wired.com/science/planetearth/magazine/16-10/ mf_bison?currentPage=1. 7. Aunapuu, M. “Spatial patterns and dynamic responses of arctic food webs corroborate the exploitation ecosystems hypothesis (EEH)” (2008). The American Naturalist 171:2. 8. Fairfax County, VA. “Deer Management Activities Fairfax County, Virginia.” http://www.fairfaxcounty. gov/comm/deer/deermgt.htm#info. Accessed October 2008. 9. Banse K. “Do we live in a largely top-down regulated world?” (2007). Journal of Biosciences 32:791-796. 10. Donlan et al 2006 Zimov SA, “Pleistocene Park: Return of the mammoth’s ecosystem” (2005). Science 308:5723. 11. Rubenstein DR at al, “Pleistocene park: does rewilding North America represent sound conservation for the 21st century?” (2006). Biological Conservation 132:232-238. 12. Ibid. fall 2008 • Harvard Science Review 17 rewilding-2.indd 17 2/9/2009 11:29:35 PM