Pleistocene rewilding is the advocacy of the reintroduction of extant Pleistocene megafauna, or the close ecological equivalents of extinct megafauna. 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.
Background
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. 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.Tim Flannery (2001), The Eternal Frontier: An Ecological History of North America and its Peoples, , pp. 344--346
Paul S. Martin (originator of the Pleistocene overkill hypothesis) 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.
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. 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. Reintroducing megafauna to North America could preserve current megafauna, while filling ecological niches that have been vacant since the Pleistocene.
Climate implications
By restoring large herbivores, greenhouse gas levels may be lowered. 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. Browsing and grazing also accelerates nutrient cycling, which may increase local plant productivity, and maintain ecosystem productivity specifically in grassy biomes. 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.
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. 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.
Yakutian horses, reindeer, European bison, plains bison, Domestic yak, moose, and Bactrian camels were reintroduced, and reintroduction is also planned for saigas, wood bison, and Siberian tigers. This project remains controversial — a letter published in Conservation Biology accused the Pleistocene camp of promoting "Frankenstein ecosystems", stating that 'the biggest problem is not the possibility of failing to restore lost interactions, but rather the risk of getting new, unwanted interactions instead.'
Extinct species with domestic descendants and relatives
A number of primitive horse races have been used as a proxy for the tarpan. Przewalski horse, a subspecies native of Mongolia and the only remaining wild horse in the world, has also been introduced in Ukraine, Hungary and France.
Robust cattle breeds or a combination of them as a proxy for the extinct aurochs. The Dutch-based TaurOs Project aims to reconstitute the aurochs by crossbreeding selected breeds, while Heck cattle and Galloway cattle have already been used in grazing projects.
Extant wild camelidae contain only three species, the Guanaco, the Vicuna, and the Wild Bactrian camel. However both New World and Old World had a diversity of camelids until the Late-Pleistocene and the early Holocene. Along with the extant wild species, domesticated members especially the Dromedary and the Bactrian camel may serve as proxies to replace their extinct ancestors and relatives among their natural ranges, including North and Central America, Siberia, from East Asia to Europe, Indian subcontinent, Middle East, and Northern Africa.
Introduced species as alternative proxy for extinct fauna
There have been discussions that introduced exotic faunas may fill empty niches of extinct faunas (at least partially) and constrain other introduced species, hence some promote conservation of these animals rather than eradication. However, an argument against the introduction of these animals is that they are sometimes very distantly related to the extinct native fauna, and artificial introduction of them may potentially involve ecological risks.
In North America, treatments of mustangs and burros have been discussed for decades, and additional medium and large faunas may also serve to American and Canadian ecosystems for certain extents. Such animals include feral cattles, feral pigs, feral goats, Barbary sheeps, Himalayan tahrs, oryxes, nilgai and other antelopes, deer, and so on.
In Australia, a continent which had lost most of native megafauna, variety of exotic faunas most notably the Dromedary camel (as a proxy for Diprotodon and Palorchestes) may potentially compensate for missing niches, although they are very distant from the marsupials.Chris Johnson, 2019, Rewilding Australia , Australasian ScienceArian Wallach, 2014, Red Fox , Dingo for Biodiversity ProjectArian Wallach, Daniel Ramp, Erick Lundgren, William Ripple, 2017, From feral camels to 'cocaine hippos', large animals are rewilding the world , Misha Ketchell, The Conversation There is an experimental yet controversial management of feral donkeys in Western Australia which may be counted as a form or megafaunal rewilding.Monique Ross and Ben Cheshire, November 4, 2024, Meet the defiant grazier using feral donkeys to regenerate his land at Kachana Station in an 'illegal' experiment, Australian Broadcasting Corporation
The same can be said for Central and South Americas, that have also lost most of its native megafaunas and instead hosts introduced ones, while feral horses may serve as direct proxy for Hippidion.
In contrast, the "moa vs. deer" concept for New Zealand has been a topic of discussions and is more challengeable as the country naturally lacked terrestrial mammalian megafaunas.David M. Forsyth, Janet M. Wilmshurst, Robert B. Allen, David A. Coomes, 2010, Impacts of introduced deer and extinct moa on New Zealand ecosystemsKate Guthrie, April 25, 2019, Moa vs Deer – are they so different?, Predator Free NZ TrustBeth Daley, October 19, 2022, Despite the myth, deer are not an ecological substitute for moa and should be part of NZ's predator-free plan, The ConversationHannah Rae, February 6, 2022, NZ Hunter - Deer Vs Moa, EverandFarah Hancock, April 14, 2019, Deer are not like moa, NewsroomRebekah White, Too much browsing, New Zealand GeographicAdrian Currie, April 3, 2017, Much Ado About Niches, Extinct
Criticism 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.
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. Another method of Pleistocene rewilding is by using de-extinction, bringing extinct species back to life through cloning.
Pleistocene rewilding on continents
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". 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.
The proxies which may be used for this project(s) are:
Animals already introduced
Fallow deer, reintroduced from Anatolia in most parts of Europe already in Ancient times. 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). Musk ox, reintroduced in 1976 to Russia (Taimyr Peninsula and Wrangel Island) and Scandinavia. European bison, saved from extinction in zoos in the early 20th century and reintroduced in several places of Eastern Europe. Northern bald ibis, extinct in southern Europe during the Modern Age, has reintroduction projects underway in Austria and Spain. Water buffalo, reintroduced in several areas including Danube Delta (present in the Danube basin in the early Holocene period and a proxy for the similar Bubalus murrensis which was widespread in southern Europe during the warmer periods of the Pleistocene; domestic populations exist in Italy and the Balkans). Alpine marmot, reintroduced with success in the Pyrenees in 1948, where it had disappeared at end of the Pleistocene epoch.
Animals with existing populations that are expanding Alpine ibex Spanish ibex Chamois Moose Wolf Eurasian lynx Iberian lynx Brown bear European mink Mediterranean monk seal European beaver Osprey White-tailed eagle Griffon vulture Eurasian black vulture Eurasian eagle owl
Species still extant outside Europe 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) Asian elephant (Proxy for the extinct Straight-tusked elephant, also historically present in Turkey. The Randers Tropical Zoo in Denmark plans on using Asian elephants on a small scale local rewilding project) Dhole (Occurred during Late-Glacial Period) Hippopotamus (Occurred in Europe during the Pleistocene; suitable in warmer parts of Europe) 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.) Onager (also recently extinct in Eastern Europe) Persian leopard (Leopards thrived in Europe until the end of the Pleistocene and are still present in the Caucasus.) Saiga antelope (present in Eastern Europe until recently) Spotted hyena (Last occurrence during the Late-Glacial Period)