From feral camels to ‘cocaine hippos’, large animals are rewilding the world

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Most of the world’s wild horses, such as the Australian brumby, are outside their historic native range. Andrea Harvey

Erick Lundgren, University of Technology Sydney; Arian Wallach, University of Technology Sydney; Daniel Ramp, University of Technology Sydney, and William Ripple, Oregon State University

Throughout history, humans have taken plants and animals with them as they travelled the world. Those that survived the journey to establish populations in the diaspora have found new opportunities as they integrate into new ecosystems.

These immigrant populations have come to be regarded as “invaders” and “aliens” that threaten pristine nature. But for many species, migration may just be a way to survive the global extinction crisis.

In our recently published study, we found that one of the Earth’s most imperilled group of species is hanging on in part thanks to introduced populations.

Megafauna – plant-eating terrestrial mammals weighing more than 100kg – have established in new and unexpected places. These “feral” populations are rewilding the world with unique and fascinating ecological functions that had been lost for thousands of years.

Today’s world of giants is only a shadow of its former glory. Around 50,000 years ago, giant kangaroos, rhino-like diprotodons, and other unimaginable animals were lost from Australia.


Read more: Giant marsupials once migrated across an Australian Ice Age landscape


Later, around 12,000 years ago, the last of the mammoths, glyptodonts, several species of horses and camels, house-sized ground sloths and other great beasts vanished from North America.

In New Zealand, a mere 800 years ago, a riot of giant flightless birds still grazed and browsed the landscape.

The loss of Earth’s largest terrestrial animals at the end of the Pleistocene was most likely caused by humans.

Sadly, even those large beasts that survived that collapse are now being lost, with 60% of today’s megafauna threatened with extinction. This threat is leading to international calls for urgent intervention to save the last of Earth’s giants.

A wilder world than we think

Formal conservation distribution maps show that much of Earth is empty of megafauna. But this is only a part of the picture.

Many megafauna are now found outside their historic native ranges. In fact, thanks to introduced populations, regional megafauna species richness is substantially higher today than at any other time during the past 10,000 years.

Megafauna have expanded beyond their historic native range to rewild the world. Number of megafauna per region, in their ‘native’ range only (a) and in their full range (b) Modified and reproduced from Lundgren et al. 2017

Worldwide introductions have increased the number of megafauna by 11% in Africa and Asia, by 33% in Europe, by 57% in North America, by 62% in South America, and by 100% in Australia.

Australia lost all of its native megafauna tens of thousands of years ago, but today has eight introduced megafauna species, including the world’s only wild population of dromedary camels. Australia lost all of its native megafauna tens of thousands of years ago, but is now home to eight introduced species, including the world’s only population of wild dromedary camels. Remote camera trap footage from our research program shows wild brumbies, wild donkeys and wild camels sharing water sources with Australian dingoes, emus and bustards in the deserts of South Australia.

These immigrant megafauna have found critical sanctuary. Overall, 64% of introduced megafauna species are either threatened, extinct, or declining in their native ranges.

Some megafauna have survived thanks to domestication and subsequent “feralisation”, forming a bridge between the wild pre-agricultural landscapes of the early Holocene almost 10,000 years ago, to the wild post-industrial ecosystems of the Anthropocene today.

Wild cattle, for example, are descendants of the extinct aurochs. Meanwhile, the wild camels of Australia have brought back a species extinct in the wild for thousands of years. Likewise, the vast majority of the world’s wild horses and wild donkeys are feral.

There have been global calls to rewild the world, but rewilding has already been happening, often with little intention and in unexpected ways.

A small population of wild hippopotamuses has recently established in South America. The nicknamed “cocaine hippos” are the offspring of animals who escaped the abandoned hacienda of Colombian drug lord Pablo Escobar. Colombia’s growing ‘cocaine hippo’ population is descended from animals kept at Pablo Escobar’s hacienda.

By insisting that only idealised pre-human ecosystems are worth conserving, we overlook the fact that these emerging new forms of wilderness are not only common but critical to the survival of many existing ecosystems.

Vital functions

Megafauna are Earth’s tree-breakers, wood-eaters, hole-diggers, trailblazers, wallowers, nutrient-movers, and seed-carriers. By consuming coarse, fibrous plant matter they drive nutrient cycles that enrich soils, restructure plant communities, and help other species to survive.

The wide wanderings of megafauna move nutrients uphill that would otherwise wash downstream and into the oceans. These animals can be thought of as “nutrient pumps” that help maintain soil fertility. Megafauna also sustain communities of scavengers and predators.

In North America, we have found that introduced wild donkeys, locally known as “burros”, dig wells more than a metre deep to reach groundwater. At least 31 species use these wells, and in certain conditions they become nurseries for germinating trees. Introduced wild donkeys (burros) are engineering the Sonoran Desert, United States.

The removal of donkeys and other introduced megafauna to protect desert springs in North America and Australia seems to have led to an exuberant growth of wetland vegetation that constricted open water habitat, dried some springs, and ultimately resulted in the extinction of native fish. Ironically, land managers now simulate megafauna by manually removing vegetation.

It is likely that introduced megafauna are doing much more that remains unknown because we have yet to accept these organisms as having ecological value.

Living in a feral world

Like any other species, the presence of megafauna benefits some species while challenging others. Introduced megafauna can put huge pressure on plant communities, but this is also true of native megafauna.

Whether we consider the ecological roles of introduced species like burros and brumbies as desirable or not depends primarily on our own values. But one thing is certain: no species operates in isolation.

Although megafauna are very large, predators can have significant influence on them. In Australia, dingo packs act cooperatively to hunt wild donkeys, wild horses, wild water buffalo and wild boar. In North America, mountain lions have been shown to limit populations of wild horses in some areas of Nevada.

Visions of protected dingoes hunting introduced donkeys and Sambar deer in Australia, or protected wolves hunting introduced Oryx and horses in the American West, can give us a new perspective on conserving both native and introduced species.

Nature doesn’t stand still. Dispensing with visions of historic wilderness, and the associated brutal measures usually applied to enforce those ideals, and focusing on the wilderness that exists is both pragmatic and optimistic.

After all, in this age of mass extinction, are not all species worth conserving?


This research will be presented at the 2017 International Compassionate Conservation Conference in Sydney.

Erick Lundgren, PhD Student, Centre for Compassionate Conservation, University of Technology Sydney; Arian Wallach, Chancellor’s Postdoctoral Research Fellow, Centre for Compassionate Conservation, University of Technology Sydney; Daniel Ramp, Associate Professor and Director, Centre for Compassionate Conservation, University of Technology Sydney, and William Ripple, Distinguished Professor and Director, Trophic Cascades Program, Oregon State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Rewilding isn’t about nostalgia – exciting new worlds are possible

Paul Jepson, University of Oxford

The restoration of natural ecosystems – “rewilding” – ought to be a chance to create inspiring new habitats. However the movement around it risks becoming trapped by its own reverence of the past; an overly nostalgic position that makes rewilding less realistic and harder to achieve.

The recent launch of Rewilding Britain is certainly exciting and timely. However George Monbiot’s vision of bringing back 15 iconic species falls short of the rewilding visions being discussed in universities.

These are emerging from advances in functional ecology and Earth system science. The vision of rewilding is more ambitious: it is about restoring ecological processes through reassembling the species that drive them. For example rooting by wild boars has repercussions throughout a woodland ecosystem. Such animals shouldn’t be reintroduced simply because they were once there, but because they could do something productive in future.

Don’t go native

Monbiot’s quest to restore “lost” species harks back to a past age. However many conservation scientists are more relaxed concerning the question of “nativenes”. They are willing to consider introducing non-native species if they contribute a functional role in ecosystems, and they view the past not as a benchmark to preserve or replicate but as an inspiration for ecosystem restoration.

For instance, “Monbiot’s 15” omits the auroch and tarpan which are classed as extinct. However in the 1980s progressive Dutch ecologists realised that their functional analogues survived as cattle and ponies and their ecological role could be restored through “de-domestication”.

They set about de-domesticating them at the famous Oostvaardersplassen reserve located a 40 minute drive from Amsterdam. This produced a “Serengeti-like” landscape: a type of nature unknown to Europe since humans settled down and started farming.

The auroch (or ‘heck cattle’) is king of the OVP.
Jan Nijendijk, CC BY-SA

The OVP, as it is known, made nature conservation political again and has become a landmark public experiment in ecology. I first visited it with a group of students in 2003 when we travelled to the Netherlands to meet the radical ecologist Frans Vera and engage with the controversies created by rewilding.

The OVP is created on reclaimed land and opponents argued that the fences and flood control created an artifical landscape that undermined any claims to its authenticity as a restored ecosystem. More seriously the policy of allowing the cattle and ponies to die of “natural” starvation enraged animal welfare and farmer groups who believed they should be subjected to the same welfare standards applied to animals in labs, farms and zoos.

The controversies surrounding the experiment, Vera’s hypothesis that Europe’s original vegetation was wood-pasture rather than high-forest, and other radical rewilding visions are inspiring a re-examination of the fundamental premise of nature conservation.

Rewilding’s big chance

I recently published a Rewilding agenda for Europe in the journal Ecography, as my contribution to the European Council’s “fitness check” of its nature legislation. The Birds and Habitats directives under review derive from the science and policy context of the 1970s. They are ageing. Both science and society have moved on.

Any revisions to European nature legislation should support the creation of experimental rewilding sites. Across the UK we could imagine the creation of wild cattle and pony step-lands on the Ridgeway, wild boar and deer-driven woodland ecosystems in Wales, and a Scottish arcadia of bison, moose, wolves and pine forest.

Wild boars in Wales?
vlod007, CC BY

We also need many more OVP-like public rewilding experiments close to urban areas. These would be contained sites that inspire and inform the public about scientific advances, and provoke us all to ask: what sort of nature do we want for the future?

Rewilding might offer fresh solutions to intractable conservation problems. For example, conservationists want to remove pine trees introduced to the Sefton Coast dune system near Liverpool but local residents love them for their scenic grandeur and red squirrels. The famous Formby footprints dating from 2,500 BC show that humans, wild cattle, deer and wolf once inhabited these coastal areas. Suggesting the reintroducing of wild cattle and companion herbivores and seeing what happens might prompt a unified vision for the dunes.

In practice rewilding is constrained by regulations on biohazards, public access and animal husbandry – and rigid and powerful 20th century conservation legislation and agencies which have no real incentive to innovate.

Conservation institutions need to modernise but no one wants to dismantle them and start over. We need designated spaces with regulatory flexibility – experimental rewilding sites – where we can plan future natures that will improve the quality of life for people and the planet.

Ordinary people are disenfranchised. Conservation policy is influenced by a coordinated lobby of a few big charities who have built their organisational models on the institutional structures of the late 20th century. George Monbiot’s vision catches the attention but advocates of rewilding need to develop realistic policy mechanisms to take their ideas forward. Rewilding experiments would give space for wider reflection and debate and give our conservation institutions time to adapt. Crucially they would reinvigorate conservation as a cultural force in the 21st century.

The Conversation

Paul Jepson is Course Director, MSc Biodiversity, Conservation and Management at University of Oxford.

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