Monday, April 18, 2016

Ghost World - Part II: Revival

In my last post, I described how the modern-day world is a global version of a ghost town: the extinction of dozens of species of large animals at the end of the Pleistocene Epoch left ecosystems incomplete and unbalanced. Without mammoths, ground sloths, and the rest, some plants and animals have thrived, others have suffered or disappeared altogether, and even natural processes like fire and climate have been affected. The natural world is incomplete without them, and continues to degrade like an abandoned village.

Of course, the key to “fixing” a ghost town is quite simple: bring people back. They don’t even have to be the same people. Just about anyone can tend the overgrown gardens, drive the disused cars, and shoo away the rats and roaches. The same may be true of our ecosystems, which brings me to an ambitious – and controversial – conservation idea:

Pleistocene Rewilding.

The concept of “rewilding” is a popular one in modern wildlife conservation. The idea is to re-establish ecosystems and populations that modern humans have destroyed or diminished. For example, the American Prairie Reserve aims to re-create the vast prairie environments of the American past, and hopes to populate that prairie with large herds of bison and other animals. Across the pond, Rewilding Europe is on a similar mission to re-establish European bison and wild horses in an attempt to stabilize wild ecosystems.

But some conservationists argue that these modern efforts aren’t ambitious enough. Most modern efforts aim to “reset” ecosystems to a few centuries ago (in North America for example, the common baseline is the late 1400s, when European settlers showed up), but some point out what I discussed in Part I of this series – ecosystems have been in trouble for a lot longer than that. What if instead, we could reset ecosystems several thousand years back, to the end of the Pleistocene, before all the megafauna went extinct?

This idea was made famous recently with the writings of Josh Donlan and colleagues in 2005 and 2006. Their plan is to re-fill the world with the kind of diverse, stable ecosystems that existed at the end of the last Ice Age. This is Pleistocene rewilding.

This image, one of the famous cave paintings of Lascaux, France, shows some of the
large herbivores our ancestors lived alongside in Europe: wild horses, deer, and the mighty aurochs.
Are these inspiring ecosystems truly gone forever, or can we restore them?
"ByProf saxx - Own work, CC BY-SA 3.0" From Wikimedia Commons.
The first steps of this environmental makeover are already underway as part of “standard” rewilding efforts. Around the world, conservationists have already expanded the wild ranges of animals such as wild horses in Asia, Bolson tortoises in North American deserts, and condors in the American west, all populations that had recently become greatly diminished. But how do we go about "rewilding" populations from the Pleistocene that are totally extinct?

The solution may be to substitute those extinct species with living ones.. In place of the Pleistocene horses and camels that roamed North America and Europe, Donlan and colleagues envision modern-day wild horses, asses, and Asian camels established in their place. And in place of the mammoths that once stomped around in the North, these Pleistocene rewilders suggest transplanting elephants – yes, elephants – to the American and Eurasian plains.

If you’re hesitant about this idea, you’re not alone. Bringing foreign species to a new land in the hopes of replacing extinct species is a plan wrought with uncertainty and difficulty. But it isn’t unheard of. Tortoises living on certain islands in the Indian Ocean have been transplanted to other islands to replace tortoise species that have gone extinct, and not only have these proxy tortoises become successful inhabitants, their presence has improved dispersal and growth of island plant life. Similarly, North American peregrine falcons populations, greatly diminished around the middle of last century, were restored using representatives from foreign subspecies around the world.

Meanwhile, in Russia, a man named Sergey Zimov and his colleagues are on a mission to test the idea of creating such “Frankenstein” Pleistocene ecosystems. To do so, they have set up a sort of biological preserve where they have gradually built up populations of several large herbivores - horses, bison, muskox, reindeer, and moose, so far – and monitored their effects on the region. They call it Pleistocene Park (naturally), and already the presence of these megafauna has allowed the expansion of grasslands and has even affected the retention of permafrost important for locking carbon in the soil. The ultimate goal is to use Pleistocene Park to restore the Mammoth Steppe ecosystems that went extinct in the Pleistocene.

In Europe, some efforts are taking the idea a step further and aiming to “recreate” ancient species. Wild horses and bovines may be technically extinct, but their domesticated descendants still hold their genetic legacy. Rewilding Europe is working to “undomesticate” horses by breeding for traits closest to those of their wild ancestors, and the Tauros Programme is an effort to breed the wildest characteristics into cattle to restore an approximation of their much-more-impressive predecessors, the aurochs. Before long, these “re-evolved” versions of ancient large herbivores may be able to roam the restored ecosystems of Europe.

Pleistocene Park is already home to horses, bison, muskox, moose, and reindeer,
with more animals to come in the future. The Park serves as a testing ground for
Pleistocene rewilding. This may be the first place in the world to restore the Mammoth
Steppes of the Pleistocene. Image from here.
As you can see, efforts are already underway to restore large herbivores and diverse plant-life to their former Pleistocene glory. But something very important is missing from Pleistocene rewilding so far. Just as large herbivores are needed to keep plants in check, so large carnivores are needed to mediate the herbivores. And if you think introducing camels and elephants to the north will meet resistance, imagine the volume of objections to the notion of lions and cheetahs running alongside them.

Yet this is exactly what Donlan and colleagues call for. Back when North America was home to mammoths, wild horses, camels, and more, it was also home to many large carnivores, including the American lion and the American cheetah, which helped to control the populations of large herbivores alongside. The extinct cheetah is even thought to be the reason for the modern-day pronghorn’s incredible speed, which is unmatched by any living predator in its habitat. Important interactions like this may prove vital to restored stable ecosystems. You can't have widespread bison, mammoths, and moose without wolves, bears, and big cats to supplement them.

But this whole idea is controversial for a lot of reasons, besides the obvious dangers of introducing large animals to a new place. Our long history of transporting wildlife has shown how introduced species can bring disease with them, and can have myriad unintended effects on the local ecosystems. And on top of that, we have little way of knowing if these introductions will work. Do we know enough about these animals to establish successful populations? Are these modern-day proxies close enough to their extinct relatives to successfully supplant them? And without the answers to these questions, will Pleistocene rewilding ever get enough social and political support to take off?

The answer to all of these concerns is research. This isn’t something that will happen overnight. The projects I described above are proceeding slowly and carefully. European efforts will show if “re-creating” wild horses and aurochs is possible. Pleistocene Park continues to expand, its environmental changes are constantly monitored, and Zimov and friends hope to add more species, including camels, yaks, and eventually Siberian tigers. 

Pleistocene rewilding is the ultimate in ecosystem engineering, and with the right mix of caution and ambition, we might just be able to do it right. If we do, we may restore Earth’s ecosystems to a state of health they haven’t experienced for thousands of years, while at the same time providing endangered large animals new places to thrive. The day might not be too far-off that a North American safari can trek through a Wild West where the buffalo roam across rich plains alongside elephants, lions, wild horses, pronghorns, wolves, camels, and more.

That sounds pretty incredible to me. What do you think?

(At this point, you may be wondering: Wait, can't we just bring extinct animals back to life? If so, join me in Part III of this series, where we'll explore de-extinction.)


Donlan et al. 2006. Pleistocene Rewilding: An Optimistic Agenda for 21st Century Conservation. The American Naturalist. (PDF)

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