The mammoths have vanished, so what do we do now? An obvious answer is to realize the ecological and intrinsic importance of today’s surviving megafauna and do our best to protect them, but a group of scientists have gone one (controversial) step further: they want to ‘broaden the underlying premise of conservation from managing extinctionto encompass restoring ecological and evolutionary processes’ (Donlan et al 2006: 660). They argue for the introduction of Pleistocene rewilding in North America, which involves:
- Reintroducing modern species descended from Pleistocene species that once lived in North America OR
- Reintroducing ecological proxies for Pleistocene species if the above do not exist
This paper by Donlan et al (2006) summarizes the key arguments supporting Pleistocene rewilding in North America.
Megaherbivores and large carnivores play important roles in ecosystems and have been dominant in ecosystems for the past 200 million years, until their widespread extinction in the late Pleistocene. Given their instrumental roles (See also my previous blog post on the role of megaherbivores and extinction consequences), it must follow that restoring them would have positive benefits.
Large predators’ roles include the following:
- Buffering against climate change: To cite a contemporary example, evidence from a Wilmers and Getz (2005) paper shows that the reintroduction of gray wolves have helped maintain carrion availability for the survival of other scavenger species, important since snow thaws earlier in Yellowstone due to climate warming.
- Controlling disease (some of which can spread to humans): Another contemporary example concerns the lyme disease epidemic (spread to humans by ticks) which occurred in North America in the early 2000s was probably caused by peak populations of white-tailed deer, once kept under control by gray wolves.
Evolutionary and Conservation Benefits
Pleistocene rewilding is a way to transform conservation biology from mere preservation of existing species to reconstructing ecosystem processes and species interactions. Donlan et al (2005) argues that what is ‘natural’ must be challenged; we often think of the 1492 Columbian landfall on America and the state of the environment then as what is a ‘natural benchmark’ for conservation, but this fails to recognize the rich biodiversity of the late Pleistocene period. There are also additional positive benefits from maintaining large viable populations of target species to facilitate adaptation to climate change. North America could provide an additional refugia for conserving the genetic proxies of Pleistocene megafauna (such as Asian elephants, a proxy for mastodons), since these are endangered in Asia and Africa, the only 2 continents which preserve a large diversity of megafauna.
Criticisms (Rubenstein et al 2006)
Effects on Ecosystems are Unpredictable
We do not really understand how Pleistocene ecosystems functioned and therefore should not attempt to reconstruct them. Rather, Pleistocene rewilding may disrupt contemporary ecosystems, e.g. by introducing new diseases, etc. Also, the effect of introducing ‘exotic’ species is unknown. Even when reintroducing native species, their effects on the ecosystem are unpredictable. For example, the introduction of one-humped camel in wreaked havoc on Australia’s desert ecosystems as they selectively ate rare plant species.
Reintroductions Do Not Always Work
Many modern-day examples show that even reintroducing native species within their original geographic regions is not always successful. The most successful examples (Przewalski’s horse and the Asian ass) are those where only a short time between extinction in the wild and reintroduction, as the ecosystem would not have changed much in that time frame. In other examples, problems such as unexpected changes in environmental conditions, naivete towards predators and diseases have rendered reintroductions unsuccessful.
Will Not Restore Evolutionary Potential
Most of the species which are supposedly to be introduced as part of rewilding are genetically distinct from their ancestors, e.g. cheetahs and lions. Thus, introducing them would not help restore the evolutionary potential that once was during Pleistocene times.
Local and state governments in North America already face much trouble from people about fears over native predator attacks, e.g. cougar attacks on joggers. The introduction of exotic species such as elephants as proxies for mastodons for example would generate even more human-wildlife interactions and conflicts, such as those currently taking place in Africa.
After reading all of this, I feel that the Rubenstein paper points out many pertinent problems that rewilding poses. Rewilding of native species, on the other hand, is a more promising aim for modern conservation. Pleistocene rewilding is much more difficult and prone to ecosystem-devastating error. The difficulties in even establishing the causes of late Pleistocene megafauna extinction reveals our lack of certainty about late Pleistocene environments. Rather than trying to enforce ‘revolutionary’ ideas, I think modern conservation should focus on preserving existing environments and rewilding (where appropriate) of native species.
I would like to end off with a link to an organization supporting the contemporary re-wilding agenda. Its ideas centre mostly around preserving ‘keystone’ species like large carnivores which play important roles in regulating ecosystems.
The Rewilding Institute: think-tank which supports rewilding programmes in America
Nevertheless, the controversy surrounding rewilding and the question of whether this is right for the environment goes a long way to highlight the fact that once these magnificent giants are lost, they have almost certainly vanished for good.
Donlan, J. et al (2005) Pleistocene rewilding: An optimistic agenda for twenty‐first century conservation, The American Naturalist, 168, 5, pp. 660-681
Rubenstein, D. R. et al (2006) Pleistocene park: Does re-wilding North America represent sound conservation for the 21st century?, Biological Conservation, 132, pp. 232-238