by A new paper argues that an unscientific bias against “wild” or “invasive” animals is one of the major stabilizing trends that make ecosystems healthier.
Introduced species such as feral pigs, horses, donkeys and camels are a powerful force of “re-weeding” — reintroducing wild animals into ecosystems where humans have exterminated them — according to a study published Thursday in Science.
In many such ecosystems, large herbivores spread seeds, increase plant diversity and act as “ecosystem engineers”—and this is true whether those herbivores are “invasive” or “native,” the authors argue.
“One way to talk about this is: could a visitor from outer space, who didn’t know the history, tell what megafauna were native or introduced based on their effects alone,” said Erick Lundgren, a student doctorate in biology at Arizona State University.
Megafauna refers to animals weighing more than 44 kilograms, or about 100 pounds – a key factor, as much of the data on the malignant nature of “invasives” generally rests on research done on small animals, plants and pathogens.
In the case of large animals, however, if our alien visitor couldn’t tell the difference, Lundgren said, “then the native is not a helpful way to understand how ecosystems work.”
The study argues against widely held beliefs about whether invasive species are harmful — or what Lundgren described as the quasi-religious view that some species inherently belong in a certain landscape and others don’t.
That belief is the driving force behind an expensive and often futile campaign since the 1990s to exterminate species including feral pigs in Texas, wild horses across the American West and donkeys and camels in Australia.
In those cull campaigns, land managers killed millions of “wild” megafauna and discussed even more severe interventions. In the case of Texas, for example, state officials proposed seeding the landscape with the poison warfarin to kill feral pigs. Ranchers argued that the poison could enter the food chain and kill scavengers or, perhaps, people who ate the colored meat.
The Science study made the case that much of this killing is unnecessary – or even harmful to the ecosystems it is supposed to protect. Introduced species have “partially counteracted” the long series of extinctions and general declines among populations of large plant-eating mammals since prehistoric times, the authors wrote.
Although they noted that these animals are thought to have “an unusually negative impact on plants compared to native megafauna,” by looking at more than 200 studies of impacts from large introduced herbivores, they found “no difference between the influence of introduced megaherbs and the influence of native megafauna.”
Instead, they found that the most important determining factor in a species’ effects on the surrounding ecosystem is its size and feeding preferences, rather than where it came from.
For example, large grazers like horses and camels tended to reduce grass diversity — but that was true whether those animals were in their home ranges or in new ecosystems abroad.
Pigs native to the forests of Eurasia do exactly what their feral cousins do in America and Poland: They root up plants, eat crops, litter the landscape and create large mud walls in their efforts to cool themselves – regardless none of them at least. the farmer’s desire to run a neat, profitable agricultural operation from the same space.
But from another perspective, these actions can be seen as beneficial to the environment – and when the animals in question are native animals, they are often portrayed as such. While disturbing existing vegetation, for example, the pigs also create space for new plant growth. Their pineapple can cause algal blooms in waterways, but that’s because it’s so rich in nutrients – meaning it’s an important source of natural fertiliser, especially for the seeds that pigs spread in the same way .
And their walls are essentially tiny pools that can help capture and retain water in arid landscapes—something ecologists consider beneficial when done by, say, bison. (Meanwhile, the trails left by African buffalo introduced to Australia have been linked to a lower frequency of destructive wildfires.)
In doing all of this, Lundgren argued, the pigs may be serving a similar function to a long-extinct species that bears similarities to the giant peccaries that once roamed the forests of America. North during the last ice age, more than 10,000 years ago.
And often, the impacts of native animals on native plants—like Western bison interfering with the recovery of aspen trees in Yellowstone—is called ecosystem engineering.
Take elephants: Native to Africa and Asia (and, once, North America) and often in conflict with local farmers because of their very different needs from the landscape – needs that, in the eyes of agriculture, make them as destructive as any generous sounder. pigs. Elephants knock things over, strip and kill trees, and eat or trample any fruits or vegetables they want.
On the one hand, it could be argued that these are beneficial functions in forests – although that has not stopped some botanists from claiming that elephants are bad for native trees and shrubs, and in some national parks in Africa, managers suggest land to kill them to preserve those species.
But no matter how destructive established species like bison or elephants are, they have one serious advantage over newer ones, Lundgren argued: Everyone understands that when biologists argue for their removal, it’s clear that what they are proposing is a priority.
“Although an invasive biologist would argue that [what they’re expressing] that they weren’t even choices – that they were somehow mandated by the world. That the world told them that those choices are real.”
Scientists have long distinguished between native organisms and newcomers — the term “neophyte” refers to a “new plant” on a particular landscape.
But the meaning of that debate changed as the number of introduced animals increased – “a global consequence of an increasingly connected world and the increase in the size of the human population,” writes invasive biologist Petr Pyšek in 2020 summary outlining the number of injuries. .
“Invasive alien species disrupt biogeographic realms, affect the richness and abundance of native species, increase the risk of native species becoming extinct,” he wrote.
This debate got ugly at times.
Proponents of “invasion biology” note the painful connections between early 20th century concerns about non-native species – such as the Nazi campaign to properly replace animals brought in by the Third Reich with Teutonic species.
But “most judgments about the aesthetics of introduced species cannot, however, be clearly connected [racist] motives,” wrote prominent ecologist David Simberloff in a 2003 article in Biological Invasions.
Contrary to Nazi claims of harm from non-Germanic species, however, “harm is readily documented,” Simberloff said.
In contrast, ecologist Mark Davis argued in Nature that it is precisely harm – and not essence – that scientists must consider when making judgments about which species to nurture and which to harvest.
Non-native traits such as their characterization of beloved “native” species have helped create a pervasive bias against alien species that has been embraced by the public, conservationists, land managers and policy makers, as well as scientists, around the world.”
This is unfortunate, 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 regard the distinction as a core guiding principle.”
Or as Brown University ecologist Dov Sax told the New York Times: “I think the dominant paradigm in the field is still a ‘when in doubt, kill them’ attitude.”
Those killings and transfers have their own unintended effects. Since the 1930s, land managers in Nevada’s Death Valley have harvested and sometimes shot burros (wild donkeys). According to the National Park Conservation Society, the burros overburden the ecosystem because they eat so much vegetation and pollute all 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 harvesting in the American West and Australia found inadvertent destruction of wetlands resulting in their extinction. was supposed to protect.
“They destroyed [the donkeys]and then wetlands filled with cattails and reeds, then dried up and went anaerobic – and all the endemic fish became endangered and the wetlands became extinct,” said Lundgren.
“And so now land managers go and clear the vegetation by hand. And despite that, they still want to wipe these animals out of all these areas.”
He notes that there is a stark contrast between this vision of a war between indigenous people and invaders and a vision often adopted by Indigenous people in both countries – who have looked to transform their ecosystems over the past several centuries.
For example, anthropologists working among the Anishinaabe of the Upper Midwest recorded 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, a site where perhaps half a million donkeys were killed, found that the Aborigines he interviewed believed that “an animal’s value lies in its ability to survive and thrive in the environment, not in its claim. to be an original component of the fauna.”
Among those communities, he said, “generally they say yes [nonnatives] everyone has the right to live in the country now.”
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 land, and many native Hawaiians are deeply attached to wild hogs, the descendants of the domestic pigs brought with them by their ancestors.
“You can even make an argument based on the history of the Earth that if we introduced elephants into western North America, that would be a perfect fit for our ecosystems, because there have always been animals like that,” he said.
(Or at least up until about 13,000 years ago.)
Lundgren argued that the decisions made about those animals – which he thinks scientists must deal with – are political or philosophical decisions, not scientific.
“If we’re going to make decisions to do things, we have to be transparent about what those values are.”
For the latest news, weather, sports, and video streaming, go to The Hill.
