Nearly 20 years ago, the first global assessment of amphibians found the animals facing widespread declines. Now, a second, updated report shows that many amphibians are still in trouble, but with some silver linings, researchers report October 4 in Nature.
“We are realistic and hopeful at the same time,” says Jennifer Luedtke, a conservationist at the International Union for Conservation of Nature, which tracks extinction risk trends for species around the world.
In particular, the wealth of data in the new report, which includes about 8,000 amphibian species, could help focus conservation efforts for years to come, says Luedtke, who also works from Washington, D.C., for Re:wild, a conservation organization based in Austin, Texas. That’s what happened after the first Global Amphibian Assessment in 2004, which brought awareness to the amphibian crisis and galvanized researchers to coordinate efforts.
Having two assessments that can be compared is a big deal, experts say. “It’s important not just to have a picture, but actually to have a sequence of pictures … where you can see what’s happening over time,” says conservation ecologist Ana Rodrigues of CNRS in Montpelier, France, who worked on the first assessment but was not involved in the second. “I’m really happy to see this done.”
Here are five big takeaways from the new report.
1. Amphibians remain more threatened with extinction than any other vertebrate group.
About 41 percent of amphibian species, which include frogs, toads and salamanders, are threatened with extinction, Luedtke and her colleagues found. That’s more than any other group of vertebrates, beating out sharks and rays (37 percent), mammals (27 percent), reptiles (21 percent) and birds (13 percent).
Amphibians held this title in 2004 too, when 39 percent of species were threatened. As part of the 2022 update, researchers also used data to reconstruct the situation in 1980. They found that even in 1980, that number was already high, at 38 percent. Basically, amphibians have been really threatened for a really long time, Luedtke says.
The most common threat that affects amphibians is habitat loss and degradation, with agriculture affecting as many as 77 percent of the studied species. Other threats include climate change and disease, each affecting 29 percent of species. Of course, “these things are never completely isolated,” says Rodrigues, and each threat may increase the likelihood of other threats.
2. Many of the worst amphibian declines are being caused by climate change now, instead of disease.
Luedtke and colleagues also wanted to know which threats were most responsible for driving the worst declines. So they looked at a subset of 788 species that, between 1980 and 2022, moved down an IUCN Red List status level — for instance, from vulnerable to endangered. They found that, in 2004, disease was the primary driver behind the drop in conservation status for 58 percent of that species subset. At the time, the fungal pathogen chytrid was devastating frog populations around the world (SN: 8/23/02). Climate change, on the other hand, was a significant contributor to declines in only 1 percent of species.
Now, less than 20 years later, climate change is behind a status drop for 39 percent of species. That makes it the most common primary driver of declines across the amphibian group, the researchers found. And still the finding is probably an underestimate, Luedtke says, as studies continue to emerge detailing how climate change–related temperature increases, changes in precipitation, extreme weather events and wildfires impact amphibians.
“It’s very worrying,” Rodrigues says. “We’re at the beginning of climate change.… What’s ahead of us?”
3. It’s bad around the world. But amphibians are doing worse in some regions than others.
Each region faces its own set of threats. The chytrid outbreak, for example, has affected much of the world, but it hit Central and South America especially hard from the 1970s to the 2000s. That likely explains why that region contains the largest proportion of species in the IUCN Red List categories of highest concern, the researchers say. New Guinea and Africa were spared much of the devastation, though the pathogen has recently started to emerge in sub-Saharan Africa.
Across Europe and East Asia, habitat loss is the leading cause of decline, followed by a newly emerging fungal pathogen in Europe called Batrachochytrium salamandrivorans, this time that affects salamanders (SN: 9/3/13). It hasn’t yet spread to North America, which would be disastrous, Rodrigues says. The continent is home to more than 200 types of salamanders, over a quarter of the world’s salamander species.
For now, North America’s amphibian declines are most associated with climate change, the report found. South and Southeast Asia are seeing an improving trend among their species’ extinction risk, probably due to better management of protected areas.
4. Scientists know a lot more about amphibians now than they did in 2004.
One of the assessment’s few bright spots is its sheer amount of data. The update includes more than 2,000 additional species — all newly described since 2004. There was also a decrease in species labeled as “data deficient” by the IUCN, from 23 percent in 2004 to only 11 percent in 2022. By comparison, though, less than 1 percent of bird species are listed as data deficient.
While there’s still a long way to go for amphibians, researchers are thrilled by the new amount of information. “It’s like, wow, all the knowledge!” Rodrigues says. “So that’s absolutely good news.” With more data, she says, conservation efforts can be better focused.
5. Some amphibian species have improved since 2004.
The new report didn’t just find declines — 120 species saw their IUCN conservation status improve.
About half of those species recovered unaided. Many of those had suffered declines due to chytrid and are now bouncing back, possibly as frogs become resistant to the pathogen (SN: 3/29/18). It’s a source of hope that “we have these little frogs evolving, in front of our eyes, resistance to chytridiomycosis,” Luedtke says.
The other half improved thanks to conservation efforts, the report found. One of those species is India’s indigo bush frog (Raorchestes indigo), which was classified as critically endangered in 2004. A couple years later, a legal battle led to the end of all mining in the Kudremukh Massif mountain range, and the species’ IUCN status has since improved to vulnerable.
Stories like that are evidence that effective habitat protection can make a noticeable difference, the researchers say, and yet, with most amphibians still facing declines, it’s clear that current efforts are not enough. The assessment’s accompanying State of the World’s Amphibians Report focuses on action steps based on the new findings. Among other things, it identifies 50 target conservation areas around the world — including Jamaica, Brazil’s Atlantic Forest and the Central Annamite Highlands in Vietnam — that feature a high density of threatened species.
“Yes, the number of threatened amphibians continues to increase, but our understanding is improving,” Luedtke says. “And because we understand them better, we can act in a more accurate and effective way.”
Source: Heart - www.sciencenews.org
