Getty images.

It’s standard news to hear about the rapid decline of wildlife these days: As humanity’s environmental impact has surged since the Industrial Revolution, animals have suffered the brunt of the consequences. But megafauna—i.e. very large animals—have been the target of human activity for much longer, and many of them went extinct thousands of years ago, often due to over-hunting. But a recent study offers unexpected signs of hope for some of these long-suffering megafauna, which make up Earth’s most imperiled group of species.

According to a study published in Ecography, megafauna, defined as plant-eating terrestrial mammals weighing more than 100 kilograms (220 pounds) on average, are establishing themselves in new and often unexpected places outside of their historic native ranges. These introduced populations would typically be considered invasive species, but the authors think a better term might be “survivors.” Furthermore, the giant animals, which include everything from hippopotamuses to donkeys, might offer unexpected benefits to their new homelands. In a recent article in The Conversation, the authors write that “these ‘feral’ populations are rewilding the world with unique and fascinating ecological functions that had been lost for thousands of years.”

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Arizona State University’s Erick Lundgren, lead author of the study, told Earther that “while the conservation community is very concerned with declines of native megafauna, we have for the most part ignored these introduced populations or considered them myopically as pests.”

“The data suggests that if we were to broaden our value system towards these organisms we would find a wilder world, full of interesting and hereto largely unstudied wildlife,” he said.

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There are 76 existing megafauna species, and according to the study, 22 of these now have introduced populations outside of their historic range. Which is good for them—because of the species that have seen new populations emerge, around two-thirds are either threatened, extinct or declining in their native ranges. A 2015 report in the journal Science Advances found that large herbivores are facing steep population declines across the planet, and that roughly 60% are threatened with extinction. This rapid decline is due to over-hunting, competition with livestock, and habitat loss through deforestation, cultivation, and development. And climate change will likely make this all the more challenging as habitats change.

In the new study, the researchers divided megafauna gains geographically and determined that introductions have increased megafauna species richness—that’s the total number of species present—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. This makes“regional megafauna species richness substantially higher today than at any other time during the past 10,000 years.”

This should not be confused with total numbers of megafauna, which continue to decrease.

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Lundgren said the real question now is if there will be “space and tolerance” for these new organisms to continue to exist in their native or non-native ranges.

“Some introduced populations are targets for eradication campaigns and others are being utilized and persecuted like native megafauna—domestic and wild donkeys are being harvested at an astonishing rate for Chinese medicine,” he said.

While some of these species, such as wild cattle, wild horses and wild camels, survived in large part due to domestication of their ancestors—helping them bridge the gap between the onset of the Holocene 10,000 years ago and today—other survival stories seem almost fictional. For instance, a small group of wild hippopotamuses has recently settled into South America after escaping Colombian drug lord Pablo Escobar’s abandoned private zoo about halfway between Medellin and Bogota. They are known as the “cocaine hippos.”

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Australia, a continent that was once rich with amazing large wildlife such as giant wombats and kangaroos, has shown the greatest gain in megafaunal diversity, since all of its native megafauna went extinct tens of thousands of years ago. Now eight species of introduced megafauna live Down Under, including the only existing population of wild dromedary camels.

In the Sonoran Desert, which occupies the Southwestern U.S. and parts of Mexico, introduced wild donkeys—which are critically endangered in their native habitat—aid local biodiversity by digging wells that provide a valuable water sources to at least 30 different mammals and birds. According to the authors, this is just one way that introduced megafauna can benefit their new surroundings.

As with all introduced or “alien” species though, the ecological impacts will be wide-ranging and not entirely predictable. More research into each of these individual occurrences will likely be needed to understand the bigger picture. Regardless, the study’s finding underscore the notion that in an era of human-dominance, we might have to start expanding our thinking on what it means for ecosystems to be ‘wild.’

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“To conserve megafauna diversity effectively we shouldn’t discount introduced or feral populations,” said Lundgren. “They also require large areas to roam—necessitating landscape scale conservation. The conservation of these animals can end up being important to many other species because by protecting these large animals’ landscapes we protect the homes of many others.”