When a species is pushed to the brink of extinction, it’s nearly impossible to bring it back. Consider the Southern Resident killer whales of the Pacific Northwest.
This genetically distinct group has dwindled to 73 whales. For decades, the animals have struggled against a plethora of external threats: shrinking numbers of the Chinook salmon they eat; a brew of toxic chemicals that accumulate in their bodies; a legacy of whales stolen to perform in aquariums; and an underwater cacophony from boats. Federal scientists recently warned that the very lack of whales threatens to drive their numbers lower, due to genetic inbreeding.
In many ways, the plight of these whales was predictable. Yet, federal endangered species protections didn’t kick in until 2005, when fewer than 80 remained.
Some scientists hope to help avoid the last-gasp desperation that often accompanies such crises by creating a sort of early warning system alerting policymakers to species that are most likely to be in peril decades from now. “What we need is some way of anticipating species that may not be threatened at the moment but have a high chance of becoming threatened in the future,” said Marcel Cardillo of Australian National University. “Prevention is better than cure.”
Cardillo and several other scientists created a computer-driven version of an extinction crystal ball for the world’s mammals that don’t live in the ocean. They compiled information about two key biological factors for how likely they are to become endangered: how big the animal is, and how much land they occupy. Bigger bodies tend to correspond to higher risk. Such species often produce fewer young less frequently, making it hard for them to bounce back. A smaller range also leaves animals more vulnerable to harm if they lose still more of their habitat.
By combining these two factors, the scientists identified species especially vulnerable to the major forces driving extinctions: climate change, a growing human population, and habitat destruction by land uses such as farming.
Using computer-generated predictions of how these external threats will evolve worldwide during the 21st century and how they would overlap with each species, the scientists looked for animals that were vulnerable to at least two different extinction drivers. Those, they labeled as being at high risk in the future.
Using that approach, as many as 20% of the world’s non-marine mammals—1,057 species—will be at high risk of extinction by 2100, the scientists predicted in a new paper in Current Biology.
Two areas are hotspots for future extinctions: tropical Africa and southern Australia. Sub-Saharan Africa stands out because all the major threats converge there, according to the researchers. Over the next four decades the region is expected to account for half the world’s population growth and over half the expansion of farmland. At the same time, median temperatures are projected to increase by 1.5 time the global average by 2100. Of 619 species there, 31% are expected to encounter both a rapid increase in land-use changes and swift shrinking of their range due to warming. In addition, “there are a lot of large mammal species that are likely to be more sensitive to these things,” said Cardillo. “It’s pretty much the perfect storm.”
As one example, the scientists point to the grey-cheeked mangabey, a monkey that lives in tropical forests in central Africa. Today, it’s listed as “vulnerable” by the International Union for Conservation of Nature—near the middle of spectrum of ratings that range from “least concern” to “extinct.” The IUCN notes that the spread of roads and farms exposes it to more hunting. But in the future, the scientist’s new approach warns this species is at high risk from every variable.
While Australia isn’t expected to have a similar surge in the human population, the southern and eastern parts of the continent have large concentrations of particularly vulnerable animals, coupled with predicted major land-use changes and climate-driven shrinking of which places certain mammals can survive.
What to do with these predictions? They could help guide decisions about where to protect habitat. “There’s an important part to play for broad-scale modeling studies because they can provide a broad framework and context for planning,” said Cardillo.
On that front, sub-Saharan Africa does have a few advantages. When the researchers looked at how existing wildlife reserves overlap with where high-risk species live, they found that more of the animals in Africa met protection targets than in many other parts of the world. The scientists temper that news with warnings that a push to expand such reserves in Africa risks exacerbating controversies about potential harms to people living in the area. “It will be a challenge to expand the network in a way which achieves biodiversity protection outcomes while respecting or enhancing Indigenous rights,” they write.
No computer algorithm can foretell how these efforts—and the fates of the species relying on them—will fare over the course of this century.
Cardillo, et. al. “Priorities for conserving the world’s terrestrial mammals based on over-the-horizon extinction risk.” Current Biology. April 10, 2023.
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