The 20 Animal Species That Could Rewild the World

(Bloomberg) -- Reintroducing just 20 large mammal species to their historic habitats could boost biodiversity across a broad swathe of the planet while helping to stabilize the climate, according to a new study.

“Solving the biodiversity crisis and the climate crisis is not only necessary, they're mutually reinforcing,” said Carly Vynne, a conservation biologist and lead author of the paper published Jan. 27 in the journal Ecography.

That's because biodiverse ecosystems are both more resilient to climate change and store more carbon dioxide from the atmosphere, research has shown. Yet climate change is exacerbating what some scientists call “the sixth great extinction.” The United Nations in 2019 warned that “nature is declining globally at rates unprecedented in human history” with a million species at risk of vanishing.

Predators and other large animals are landscape architects, influencing the growth of carbon dioxide-absorbing vegetation. Scientists have documented, for instance, how the return of gray wolves to Yellowstone National Park in 1995 reshaped the ecosystem by keeping plant-munching elk populations in check. That has allowed willows and other trees to flourish, resulting in growing numbers of beaver and bison.

“Large herds of mammals are themselves also carbon storage basins,” said Vynne.

Scientists have calculated that restoring densities of predators worldwide could result in landscape changes that could sequester 23 gigatons of atmospheric carbon.

From 298 Species to 20

Vynne and a team of researchers identified 298 large mammal species and their ranges, analyzing satellite data to determine the presence of suitable habitat in 730 terrestrial ecoregions. An ecoregion is a conservation planning tool that identifies similar plant and animal communities in a particular area.

The scientists then focused on ecoregions that were missing just one to three large mammal species that historically had occupied more than 80% of the area, reasoning it would be feasible to reintroduce those animals within five to 10 years.

They whittled down the list of large mammals to the 20 that would have the most impact, triggering the complete restoration of large animal clusters over 54% of the world's landmass.

Seven of the species are predators, such as jaguars, wolverines and cougars, and 13 are herbivores such as pampas deer, hippopotamuses and gazelles. The animals are found on five continents and reintroducing them would expand the range of nine threatened species, according to the study.

Bringing back the Eurasian beaver, European bison, reindeer and wolf to Europe, for instance, could dramatically expand the range of complete collections of large animals.

Predator Problems

Reintroducing predators, though, can be politically fraught. The return of the gray wolf in the United States has led to decades of conflict over the predators' killing of livestock.

Wildlife ecologist Euan Ritchie, a professor at Deakin University in Melbourne, Australia, who was not involved in the research, said the paper's prioritization of animals to reintroduce was valuable. “I think it's a really important be aware of where there are gains to be potentially had in bringing species back.”

However, restoring animals long gone from an ecosystem is challenging. “There's a number of complexities when you're talking about large carnivores in particular,” said Ritchie. “They need suitable prey so you might need to restore prey as well as predator populations at the same time.”

Predators also roam over large territories and may cross local and national borders, requiring cooperation among governments and landowners.

“It's definitely not a case of just grabbing some large carnivores or herbivores and plugging them back into the ecosystem,” said Ritchie. “There's a lot of thought that will need to go into this.”