Feral pigs and donkeys can be more of a savior than a plague for ecosystems, research shows

An unscientific bias against “wild” or “invasive” animals threatens to undermine one of the great stabilizing trends that are making ecosystems healthier, a new paper argues.

Introduced species such as feral pigs, horses, donkeys and camels represent a powerful force of “rewilding” – the reintroduction of wild animals into ecosystems where humans had exterminated them – according to a study published Thursday in Science.

In many such ecosystems, large herbivores disperse seeds, increase plant diversity and act as “ecosystem engineers” – and that’s true regardless of whether those herbivores are “invasive” or “native,” the authors argue.

“One way to talk about this is whether a visitor from space, who didn’t know the history, could tell which megafauna are native or introduced based solely on their effects,” said Erick Lundgren, a doctoral student in biology at Arizona . State University.

Megafauna refers to animals that weigh more than 44 kilograms, or about 100 pounds – a key factor, because much of the data on the virulent nature of “invasive species” in general relies on research done on small animals, plants and pathogens.

But in the case of large animals, if our alien visitor couldn’t tell the difference, Lundgren said, “then nativeness is actually not a useful way to understand how ecosystems work.”

The study argues against widely held views about whether invasive species are harmful – or against what Lundgren described as the quasi-religious perception that some species inherently belong in a given landscape and others do not.

That belief is the driving force behind a wave of expensive and often futile campaigns since the 1990s that are wiping out species including wild boars in Texas, wild horses in the American West and donkeys and camels in Australia.

In these cull campaigns, land managers have killed millions of ‘wild’ megafauna and discussed even more drastic interventions. In the case of Texas, for example, government officials proposed seeding the landscape with the poison warfarin to kill wild hogs. Ranchers argued that the poison could enter the food chain and kill scavengers, or possibly people who ate the contaminated meat.

The Science study shows that many of these killings are unnecessary – or even harmful to the ecosystems they are supposed to protect. Introduced species “have partially reversed” the long-term series of extinctions and general declines among populations of large herbivorous mammals since prehistoric times, the authors wrote.

Although they noted that these animals are “expected to have unusually negative impacts on plants compared to native megafauna,” by looking at more than 200 studies on the impacts of large, introduced herbivores, they found “no differences between the impacts of introduced and native megaherbivores ‘.

Instead, they found that the main determinant of a species’ effects on the surrounding ecosystem was its size and feeding preferences, not where the species came from.

For example, large grazers such as horses and camels tended to reduce grass diversity – but that was true whether these animals were in their own habitat or in new ecosystems abroad.

Native pigs in the forests of Eurasia do exactly what their wild cousins ​​in the Americas and Polynesia do: they eradicate plants, eat crops, defecate in the landscape and create large mud puddles in their attempts to cool themselves – all without the slightest regard for and the desire of farmers to run a tidy, profitable agricultural business from the same space.

But from another perspective, these actions can be seen as beneficial to the environment – ​​and if these animals are native, they are often depicted as such. For example, by disrupting existing vegetation, the pigs also create space for new plant growth. Their poop can lead to algae blooms in waterways, but that’s because it’s so rich in nutrients. That means it is an important source of natural fertilizer, not least for the seeds that pigs disperse in the same way.

And their mud holes are essentially small ponds that can help hold and retain water in arid landscapes – something ecologists consider useful when done by bison, for example. (Meanwhile, the mud puddles left by introduced African buffalo in Australia have been linked to a lower incidence of destructive wildfires.)

By doing all this, Lundgren argued, the pigs could serve a similar function to a long-extinct species they somewhat resemble: the giant peccaries that rooted and grew through North American forests during the last ice age more than 10,000 years ago. sniffed.

And often the impact of native animals on native plants – such as the western bison interrupting the recovery of aspen trees in Yellowstone – is described as ecosystem engineering.

Take elephants: native to Africa and Asia (and once to North America) and often in conflict with local farmers because of their very different needs from those in the landscape – needs that make them, in the eyes of the farmer, as destructive as any sound of wild animals. pigs. Elephants knock things over, cut down and kill trees, and eat or trample any fruits and vegetables they want.

On the one hand, these are arguably useful functions in forests – although that hasn’t stopped some botanists from claiming that elephants are bad for native trees and shrubs, and in some African national parks land managers are advocating killing them to protect those species. retain.

But no matter how destructive, established species like bison or elephants have one serious advantage over newer species, Lundgren argued: Everyone understands that when biologists argue for their removal, what they are proposing “is clearly a preference.”

“While invasion biologists claim so [what they’re expressing] are not even preferences – that they are somehow imposed by the world. That the world told them that those preferences are real.”

Scientists have long distinguished between native and new organisms; the term ‘neophyte’ refers to a ‘new plant’ in a particular landscape.

But the tenor of that debate changed as the number of introduced animals multiplied — the “global consequence of an increasingly connected world and the increase in human population size,” wrote invasion biologist Petr Pyšek in a 2020 summary that included a litany of damage was explained. .

“Invasive alien species degrade biogeographical areas, impact the richness and abundance of native species, and increase the risk of native species becoming extinct,” he wrote.

This debate has gotten ugly at times.

Opponents of “invasion biology” point to the sordid connections between early 20th century concerns about non-native species – such as the Nazi campaign to replace introduced animals in the Third Reich with truly German species.

However, “most judgments about the aesthetics of introduced species cannot be clearly related [racist] motives,” wrote leading ecologist David Simberloff in a 2003 article in Biological Invasions.

Unlike Nazi claims of damage from non-German species, modern damage is “easily documented,” Simberloff added.

In contrast, ecologist Mark Davis has argued in Nature that scientists should assess the damage – not its origins – when deciding which species to nurture and which to exterminate.

Characterizations of non-native species as driving the extinction of “beloved ‘native’ species… have helped create a pervasive bias against non-native species that has been embraced by the public, conservationists, land managers and policy makers, as well as by just as many scientists around the world.”

That’s a shame, he argued, because “the practical value of the dichotomy of native and alien species in conservation is diminishing and even becoming counterproductive. Yet many conservationists still view the distinction as a guiding principle.”

As ecologist Dov Sax of Brown University told The New York Times, “I think the dominant paradigm in this area is still a ‘when in doubt, kill them’ attitude.”

These killings and takedowns have their own unintended consequences. Since the 1930s, land managers in Nevada’s Death Valley have removed and sometimes shot burros (wild burros). According to the National Park Conservation Association, the donkeys overload the ecosystem because they eat so much vegetation and “suck up the water.”

Other evidence suggests that donkeys actually increase the water supply by digging wells that other creatures can access, and a 2007 study of donkey removal in the American West and Australia found that their eradication had led to the accidental destruction of the wetlands where they lived. had to protect.

‘They have been exterminated [the donkeys]and then the wetlands filled with cattails and reeds, then dried up and became anaerobic – and all these endangered endemic fish and these wetlands became extinct,” Lundgren said.

“And so land managers are now manually clearing the vegetation. And despite this, they are still trying to eradicate these animals from all these areas.”

This vision of a war between natives and invasive species, he notes, stands in stark contrast to the view often held by indigenous peoples in both countries – who have seen their ecosystems transformed in recent centuries.

For example, anthropologists working among the Anishinaabe of the Upper Midwest reported that many of their respondents saw the colonization of their lands by new plant “nations” as “a natural form of migration.”

And an ethnographer in the Australian Outback, where perhaps half a million donkeys were killed, found that the Aboriginal people he interviewed believed that “an animal’s value lies in its ability to live and thrive in the environment, not in its claim to an original part of the fauna.”

Among those communities, he added, “it is widely believed that [nonnatives] all now have the right to live on the land.”

Lundgren argued that these examples suggest that the question of what belongs is complex and controversial. Most Americans want wild horses and burros to remain on public lands, and many Native Hawaiians have a deep attachment to wild hogs, descendants of domestic pigs brought by their ancestors.

“You can even make an argument based on Earth’s history that if we were to introduce elephants to western North America, that would actually be very appropriate for our ecosystems, since there have always been such animals,” he said .

(Or at least until about 13,000 years ago.)

Decisions about what to do with those animals, Lundgren argued, are political or philosophical, not scientific — which he says scientists should take into account.

“If we’re going to make decisions to do things, we have to be transparent about what those values ​​are.”

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