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Pleistocene rewilding is the advocacy of the reintroduction of extant Pleistocene megafauna, or the close ecological equivalents of extinct megafauna.[1] It is an extension of the conservation practice of rewilding, which aims to restore functioning, self-sustaining ecosystems through practices that may include species reintroductions.
Towards the end of the Pleistocene era (roughly 13,000 to 10,000 years ago), nearly all megafauna of Eurasia, Australia, and South/North America, dwindled towards extinction, in what has been referred to as the Quaternary extinction event. With the loss of large herbivores and predator species, niches important for ecosystem functioning were left unoccupied.[2] In the words of the biologist Tim Flannery, "ever since the extinction of the megafauna 13,000 years ago, the continent has had a seriously unbalanced fauna". This means, for example, that the managers of national parks in North America have to resort to culling to keep the population of ungulates under control.[3]
Paul S. Martin (originator of the Pleistocene overkill hypothesis[4]) states that present ecological communities in North America do not function appropriately in the absence of megafauna, because much of the native flora and fauna evolved under the influence of large mammals.[5][6]
Ecological and evolutionary implications
Research shows that species interactions play a pivotal role in conservation efforts. Communities where species evolved in response to Pleistocene megafauna (but now lack large mammals) may be in danger of collapse.[7][8] Most living megafauna are threatened or endangered; extant megafauna have a significant impact on the communities they occupy, which supports the idea that communities evolved in response to large mammals. Pleistocene rewilding could "serve as additional refugia to help preserve that evolutionary potential" of megafauna.[8] Reintroducing megafauna to North America could preserve current megafauna, while filling ecological niches that have been vacant since the Pleistocene.[9]
By restoring large herbivores, greenhouse gas levels may be lowered.[10] Grazers may also reduce fire frequency by eating flammable brush, which would, in turn, lower greenhouse gas emissions, lower aerosol levels in the atmosphere, and alter the planet's albedo.[10] Browsing and grazing also accelerates nutrient cycling, which may increase local plant productivity, and maintain ecosystem productivity specifically in grassy biomes.[10][11] Megafauna also aid with carbon storage. The loss of megafauna that eat fruits may be responsible for up to a 10% reduction in carbon storage in tropical forests.[10]
Sergey Zimov, a Russian scientist and proponent of Pleistocene rewilding, argues that it could restore the mammoth steppe ecosystem and thus slow the melting of the Arctic permafrost and give the world more time to respond to climate change.[12] He holds that the mammoth steppe collapsed because of overhunting by humans rather than natural climate change, and has established Pleistocene Park in Siberia and Wild Field in European Russia to test grassland restoration through reintroducing mammoth steppe animals and proxies for them.[13][14]
The main criticism of the Pleistocene rewilding is that it is unrealistic to assume that communities today are functionally similar to their state 10,000 years ago. Opponents argue that there has been more than enough time for communities to evolve in the absence of megafauna, and thus the reintroduction of large mammals could thwart ecosystem dynamics and possibly cause collapse. Under this argument, the prospective taxa for reintroduction are considered exotic and could potentially harm natives of North America through invasion, disease, or other factors.[1]
Opponents of Pleistocene rewilding present an alternative conservation program, in which more recent North American natives will be reintroduced into parts of their native ranges where they became extinct during historical times.[1] Another method of Pleistocene rewilding is by using de-extinction, bringing extinct species back to life through cloning.[15]
Pleistocene rewilding on mainlands
Europe
This plan was considered by Josh Donlan and Jens-C. Svenning, and involves (as in rewilding North America) creating a Pleistocene habitat in portions of Europe. Svenning claims that "Pleistocene Rewilding can be taken for consideration outside of North America". [citation needed] Incidentally, an independent "Rewilding Europe" initiative was established in the Netherlands in 2011, with the western Iberian Peninsula, Velebit, the Danube delta and the eastern and southern Carpathians as particular targets.[16]
The proxies which may be used for this project(s) are:
Mouflon, reintroduced for hunting purposes in the continent from the island populations of Corsica and Sardinia (originated in turn by introductions from the Middle East during the Neolithic period).
Asian black bear (Until the late Pleistocene, Europe had two subspecies of its own, Ursus thibetanus mediterraneus in western Europe and the Caucasus as well as Ursus thibetanus permjak in eastern Europe, especially the Ural mountains)
Northern lion (Widespread in Europe during the Pleistocene. In historical times in southeastern Europe, ranging as far as Hungary. Can also serve as a proxy for the extinct European cave lion.)
The wood bison, the closest relative of the ancient bison which became extinct in Siberia 1,000 to 2,000 years ago, is an important species for the ecology of Siberia. In 2006, 30 bison calves were flown from Edmonton, Alberta to Yakutsk. Now they live in the government-run Ust'-Buotama reserve.
Domestic Yak Six domestic yak were brought to Pleistocene Park in 2017. It turned out that two of the Yaks were pregnant so now there are eight Yak in Pleistocene Park.
A controversial 2005 editorial in Nature, signed by a number of conservation biologists, took up the argument, urging that elephants, lions, and cheetahs could be reintroduced in protected areas in the Great Plains.[32][33] The Bolson tortoise, discovered in 1959 in Durango, Mexico, was the first species proposed for this restoration effort, and in 2006 the species was reintroduced to two ranches in New Mexico owned by media mogul Ted Turner. Other proposed species include various camelids such as the Wild Bactrian camel, and various equids such as the Prezwalski's horse.
Possible animals for reintroduction
The Bolson tortoise, the first proposed candidate for Pleistocene rewilding.The Chacoan peccaryThe MustangThe BurroThe DromedaryThe mountain tapirThe capybaraAsian elephant, the closest relative of the extinct mammoth.Modern lion, closest living relative of the American lion. In the picture an Asiatic lion.Jaguar. In the United States it has been almost extinct since the beginning of the 20th century, but it still occurs in some areas of the country.
Pleistocene rewilding aims at the promotion of extant fauna and the reintroduction of extinct genera in the southwestern and central United States. Native fauna are the first genera proposed for reintroduction. The Bolson tortoise was widespread during the Pleistocene epoch, and continued to be common during the Holocene epoch until recent times. Its reintroduction from northern Mexico would be a necessary step to recreate the soil humidity present in the Pleistocene, which would support grassland and extant shrub-land and provide the habitat required for the herbivores set for reintroduction. Other large tortoise species might later be introduced to fill the role of various species of Hesperotestudo. However, to be successful, ecologists must first support fauna already present in the region.
The plains bison and the wood bison numbered in the millions during the Pleistocene and most of the Holocene, until European settlers drove them to near-extinction in the late 19th century. The plains bison has made a recovery in many regions of its former range, and is involved in several local rewilding projects across the Midwestern United States.
The pronghorn, which is extant in most of the west after almost becoming extinct, is crucial to the revival of the ancient ecosystem. Pronghorns are native to the region, which once supported large numbers of the species and extinct relatives of the same family. It would occupy the Great Plains and other arid regions of the west and southwest.
Distributions of some of today's arctic species and their relatives were much broader during the late Pleistocene and the Holocene; reindeer reached as far as southern United States, and close relatives of muskox (Bootherium and Euceratherium and Praeovibos) extended to southern United States and Mexico. Hence reindeer and muskox might be able to inhabit northern portions of central North America.
Bighorn sheep and mountain goat are already present in the surrounding mountainous areas and therefore should not pose a problem in rewilding more mountainous areas. Mountain goats are already being introduced to areas formerly occupied by Oreamnos haringtoni, a more southern relative that went extinct at the end of the Pleistocene. Reintroducing extant species of deer to the more forested areas of the region would be beneficial for the ecosystems they occupy, providing rich nutrients for the forested regions and helping to maintain them. These species include elk, white-tailed and mule deer.
Omnivorous species considered beneficial for the regional ecosystems include the collared peccary, a species of pig-like ungulate that was abundant in the Pleistocene. Although this species (along with the flat-headed and long-nosed peccaries) is extinct in many regions of North America, their relatives survive in Central and South America and the collared peccary can still be found in southern Arizona, New Mexico, and Texas. The Chacoan peccary, which is morphologically very similar to the flat-headed peccary, might be able to replace it in areas of the Great Plains and the South.
Horses originated in North America and spread to Asia via the Ice Age land bridge, but became extinct in their evolutionary homeland alongside the mammoth and ground sloth. The Pleistocene grasslands of North America were the birthplace of the modern horse, and by extension the wild horse. North America already has feral populations of Mustang and Burro. Animals that would serve as predators of these equine species would include lions and wolves.[34]
Alongside the wild horse, camels evolved in the drier regions of North America. Although camelids are extinct in North America, they have survived in South America until today: the guanaco and vicuña, and domesticated llama and alpaca. North America links the South American camelids with those of the Old World (the Dromedary, Bactrian camel and wild Bactrian camel). Pleistocene rewilding suggests that the closest relatives of the North American species of camelid be reintroduced.[35] The candidates would be Old World camels as a proxy for Camelops, and New World camelids as a proxies for smaller species of both Hemiauchenia and Palaeolama. These species would live in the arid regions and grasslands of North America. Although small in numbers, there are feral or semi-feral camelids in North America such as Dromedary in Texas and its vicinity[36][37] and llamas among Hoh Rainforest on the Olympic Peninsula.[38][39] Free-ranging camels face predators typical of their regional distribution, which include wolves and lions.[40] The main predator of guanacos and vicuñas is the cougar.[41]
During the Pleistocene, a species of tapir (Tapirus californicus) existed in North America with many ecotypes. They became extinct at the end of the Pleistocene epoch, but their relatives survive in Asia and South America. The mountain tapir would be an excellent choice for rewilding humid areas, such as those near lakes and rivers. The mountain tapir is the only extant non-tropical species of tapir. Predators of mountain tapirs include cougars, bears, and, less commonly, jaguars.[42] Good introduction areas might include forested ecosystems of the west and east coasts, and the more scrub-like or wetland ecosystem of the south.
During the Pleistocene, large populations of Proboscideans lived in North America, such as the Woolly, Columbian and Pygmy mammoths, and the American mastodon. The mastodons all became extinct at the end of the Pleistocene epoch, as did the mammoths of North America. However, an extant relative of the mammoth is the Asian elephant. It now resides only in tropical southeastern Asia, but the fossil record shows that it was much more widespread, living in temperate northern China as well as the Middle East (an area bearing an ecological similarity to the southern and central United States). The Asian elephant is possibly a good candidate for Pleistocene rewilding in North America. Asian elephants would do well in the environments previously occupied by the Columbian mammoth.
Several species of capybaras, such as Hydrochoerus hesperotiganites and Neochoerus aesopi and Neochoerus pinckneyi, were present in North America until the late Pleistocene. Today, feral population(s) of capybara inhabit Florida[43] while breeding has not been confirmed yet. These feral animals potentially fill ecological niches of extinct capybaras,[44] and further surveys are recommended.
Pleistocene America boasted a wide variety of carnivores (most of which are extinct today), such as the short-faced bear, saber-toothed cats (e.g. Homotherium and Smilodon), the American lion, dire wolf, and the American cheetah. Some carnivores and omnivores survived the end of the Pleistocene era and were widespread in North America until Europeans arrived, such as grizzly bears, cougars, jaguars, grey and red wolves, bobcats, and coyotes.[45]Jaguars could be reintroduced back to areas of North America to control populations of prey animals. Genetic evidence suggests that the closest living relative of the American lion (Panthera atrox) is the modern lion (Panthera leo). Modern lion could act as a proxy for the Pleistocene American lion, they could be introduced to keep the numbers of American bison, equids, and camelids in check.
South America
Pleistocene rewilding of parts of Brazil and other parts of the Americas was proposed by Brazilian ecologist Mauro Galetti in 2004. He suggested the introduction of elephants (and other analogues for extinctmegafauna) to private lands in the Brazilian Cerrado and other parts of the Americas. Paul S. Martin made a similar argument in favour of taxon reaplacement, suggesting that the megafauna of North America which became extinct after the arrival of humans (e.g., mastodons, mammoths, ground sloths, and smilodons) could be replaced with species which have similar ecological roles.[46]
Pleistocene rewilding on island landmasses
Megafauna that arose on insular landmasses were especially vulnerable to human influence because they evolved in isolation from other landmasses, and thus were not subjected to the same selection pressures that surviving fauna were subject to, and many forms of insular megafauna were wiped out after the arrival of humans. Therefore, scientists have suggested introducing closely related taxa to replace the extinct taxa. This is being done on several islands, with replacing closely related or ecologically functional giant tortoises to replace extinct giant tortoises.[47]
For example, the Aldabra giant tortoise has been suggested as a replacement for the extinct Malagasy giant tortoise,[48][49] and Malagasy radiated tortoises have been introduced to Mauritius to replace the tortoises that were present there.[50] However, the usage of tortoises in rewilding experiments have not been limited to replacing extinct tortoises. At the Makauwahi Cave Reserve in Hawaii, exotic tortoises are being used as a replacement for the extinct moa-nalo,[51] a large flightless duck hunted to extinction by the first Polynesians to reach Hawaii. The grazing habits of these tortoises control and reduce the spread of invasive plants, and promote the growth of native flora.[52]
Western long-beaked echidna (specimen collected in the early 20th century in the Kimberley region of Western Australia, a possible relic population continues to exist there)
Introduced species as alternative proxy for extinct fauna
There have been discussions that introduced exotic faunas, most notably the Dromedary camel as proxy for Diprotodon and Palorchestes, may fill empty niches of extinct faunas hence some promote conservation of these animals rather than eradication. However, an argument against the introduction of these animals is that they are very distantly related to the large, extinct marsupials of the Australian megafauna.[44][56][57][58]
The European bison or the European wood bison, also known as the wisent, the zubr, or sometimes colloquially as the European buffalo, is a European species of bison. It is one of two extant species of bison, alongside the American bison. The European bison is the heaviest wild land animal in Europe, and individuals in the past may have been even larger than their modern-day descendants. During late antiquity and the Middle Ages, bison became extinct in much of Europe and Asia, surviving into the 20th century only in northern-central Europe and the northern Caucasus Mountains. During the early years of the 20th century, bison were hunted to extinction in the wild.
In zoology, megafauna are large animals. The precise definition of the term varies widely, though a common threshold is approximately 45 kilograms (99 lb), with other thresholds as low as 10 kilograms (22 lb) or as high as 1,000 kilograms (2,200 lb). Large body size is generally associated with other traits, such as having a slow rate of reproduction and, in large herbivores, reduced or negligible adult mortality from being killed by predators.
Species reintroduction is the deliberate release of a species into the wild, from captivity or other areas where the organism is capable of survival. The goal of species reintroduction is to establish a healthy, genetically diverse, self-sustaining population to an area where it has been extirpated, or to augment an existing population. Species that may be eligible for reintroduction are typically threatened or endangered in the wild. However, reintroduction of a species can also be for pest control; for example, wolves being reintroduced to a wild area to curb an overpopulation of deer. Because reintroduction may involve returning native species to localities where they had been extirpated, some prefer the term "reestablishment".
Local extinction, also extirpation, is the termination of a species in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions.
The Bolson tortoise, also called the Mexican giant tortoise, Mexican gopher tortoise, yellow-bordered tortoise or yellow-margined tortoise, is a species of tortoise from North America. Of the six North American tortoise species, it is the largest, having a carapace length of about 46 cm (18 in). It lives in a region of the Chihuahuan Desert known as the Bolsón de Mapimí, which is located in north-central Mexico.
The mammoth steppe, also known as steppe-tundra, was once the Earth's most extensive biome. During glacial periods in the later Pleistocene it stretched east-to-west, from the Iberian Peninsula in the west of Europe, then across Eurasia and through Beringia and into the Yukon in northwest Canada; from north-to-south, the steppe reached from the Arctic southward to southern Europe, Central Asia and northern China. The mammoth steppe was cold and dry, and relatively featureless, though climate, topography, and geography varied considerably throughout. Certain areas of the biome—such as coastal areas—had wetter and milder climates than others. Some areas featured rivers which, through erosion, naturally created gorges, gulleys, or small glens. The continual glacial recession and advancement over millennia contributed more to the formation of larger valleys and different geographical features. Overall, however, the steppe is known to be flat and expansive grassland. The vegetation was dominated by palatable, high-productivity grasses, herbs and willow shrubs.
Charismatic megafauna are animal species that are large—in the category that they represent—with symbolic value or widespread popular appeal, and are often used by environmental activists to gain public support for environmentalist goals. In this definition, animals such as penguins or bald eagles are megafauna because they are among the largest animals within the local animal community, and they disproportionately affect their environment. The vast majority of charismatic megafauna species are threatened and endangered by issues such as overhunting, poaching, black market trade, climate change, habitat destruction, and invasive species. In a 2018 study, the top twenty most charismatic megafauna included the tiger, lion, and elephant.
The wild horse is a species of the genus Equus, which includes as subspecies the modern domesticated horse as well as the endangered Przewalski's horse. The European wild horse, also known as the tarpan, that went extinct in the late 19th or early 20th century has previously been treated as the nominate subspecies of wild horse, Equus ferus ferus, but more recent studies have cast doubt on whether tarpans were truly wild or if they actually were feral horses or hybrids.
The Late Pleistocene to the beginning of the Holocene saw the extinction of the majority of the world's megafauna, which resulted in a collapse in faunal density and diversity across the globe. The extinctions during the Late Pleistocene are differentiated from previous extinctions by its extreme size bias towards large animals, and widespread absence of ecological succession to replace these extinct megafaunal species, and the regime shift of previously established faunal relationships and habitats as a consequence. The timing and severity of the extinctions varied by region and are thought to have been driven by varying combinations of human and climatic factors. Human impact on megafauna populations is thought to have been driven by hunting ("overkill"), as well as possibly environmental alteration. The relative importance of human vs climatic factors in the extinctions has been the subject of long-running controversy.
Rewilding is a form of ecological restoration aimed at increasing biodiversity and restoring natural processes. It differs from other forms of ecological restoration in that rewilding aspires to reduce human influence on ecosystems. It is also distinct from other forms of restoration in that, while it places emphasis on recovering geographically specific sets of ecological interactions and functions that would have maintained ecosystems prior to human influence, rewilding is open to novel or emerging ecosystems which encompass new species and new interactions.
Pleistocene Park is a nature reserve on the Kolyma River south of Chersky in the Sakha Republic, Russia, in northeastern Siberia, where an attempt is being made to re-create the northern subarctic steppe grassland ecosystem that flourished in the area during the last glacial period.
Paul Schultz Martin was an American geoscientist at the University of Arizona who developed the theory that the Pleistocene extinction of large mammals worldwide was caused by overhunting by humans. Martin's work bridged the fields of ecology, anthropology, geosciences, and paleontology.
Evolutionary anachronism, also known as "ecological anachronism", is a term initially referring to attributes of native plant species that seemed best explained as having been favorably selected in the past due to their coevolution with plant-eating megafauna that are now extinct. Diminished effectiveness and distance of seed dispersal by fruit-eating mammals inhabiting the same ecosystems today suggest maladaptation. Maladaptation of such fruiting plants will intensify as ongoing climate change shifts the physical and ecological conditions within their current geographic range.
De-extinction is the process of generating an organism that either resembles or is an extinct species. There are several ways to carry out the process of de-extinction. Cloning is the most widely proposed method, although genome editing and selective breeding have also been considered. Similar techniques have been applied to certain endangered species, in hopes to boost their genetic diversity. The only method of the three that would provide an animal with the same genetic identity is cloning. There are benefits and drawbacks to the process of de-extinction ranging from technological advancements to ethical issues.
Rewilding Europe is a non-profit organization based in Nijmegen, the Netherlands, dedicated to creating rewilded landscapes throughout Europe. The group's efforts have contributed to increasing the stock of previously endangered species such as the European bison and the Iberian lynx.
The wood-pasture hypothesis is a scientific hypothesis positing that open and semi-open pastures and wood-pastures formed the predominant type of landscape in post-glacial temperate Europe, rather than the common belief of primeval forests. The hypothesis proposes that such a landscape would be formed and maintained by large wild herbivores. Although others, including landscape ecologist Oliver Rackham, had previously expressed similar ideas, it was the Dutch researcher Frans Vera, who, in his 2000 book Grazing Ecology and Forest History, first developed a comprehensive framework for such ideas and formulated them into a theorem. Vera's proposals, although highly controversial, came at a time when the role grazers played in woodlands was increasingly being reconsidered, and are credited for ushering in a period of increased reassessment and interdisciplinary research in European conservation theory and practice. Although Vera largely focused his research on the European situation, his findings could also be applied to other temperate ecological regions worldwide, especially the broadleaved ones.
Colossal Biosciences Inc. is an American biotechnology and genetic engineering company working to de-extinct the woolly mammoth, the Tasmanian tiger, the northern white rhinoceros, and the dodo. In 2023, it stated that it wants to have woolly mammoth hybrid calves by 2028, and wants to reintroduce them to the Arctic tundra habitat. Likewise, it launched the Tasmanian Thylacine Advisory Committee, a thylacine research project to release Tasmanian tiger joeys back to their original Tasmanian and broader Australian habitat after a period of observation in captivity.
Celtic Rewilding, formally known as Celtic Reptile & Amphibian, is a conservation company, established in 2020, by Harvey Tweats and Tom Whitehurst, with the initial aim of reintroducing extinct reptiles and amphibians back to rewilding projects within the UK. However, the company's scope has since broadened to all lost species of the UK and northern Europe. It is based in Leek, Staffordshire.
↑ Donatti, C.I.; M. Galetti; M.A. Pizo; P.R. Guimarães Jr. & P. Jordano (2007). "Living in the land of ghosts: Fruit traits and the importance of large mammals as seed dispersers in the Pantanal, Brazil". In Dennis, A.; R. Green; E.W. Schupp & D. Wescott (eds.). Frugivory and seed dispersal: theory and applications in a changing world. Wallingford, UK: Commonwealth Agricultural Bureau International. pp.104–123.
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