Study shows dire outlook for amphibians: 40% threatened with extinction

The Tepequém frog (Anomaloglossus tepequem) used to be seen in abundance in streams in the Serra do Tepequém, in the state of Roraima. Endemic to Brazil and this specific locality, found only here and nowhere else on the planet, it is believed to have disappeared from the wild. This Amazonian species has never been seen again since the 1990s.

This frog is one of 26 classified as possibly extinct in the country, according to the latest global study of amphibians by the International Union for the Conservation of Nature Species (IUCN). And the numbers are frightening. Two out of five of them are threatened.

More than a thousand experts from around the world took part in the study. It analyzed 8,000 species of amphibians — including toads, frogs, salamanders, blind snakes and others — almost 3,000 more than in the last analysis, carried out in 2004.

The galaxy frog (Melanobatrachus indicus), on the left, is one of India’s rarest species, rediscovered only in 1997. On the right, the Indian Ghatixalus asterops is also considered endangered. Images courtesy of Sandeep Das/IUCN.

The highlight this time is the increasing role of climate change in the global decline of amphibians, considered the most threatened of all vertebrate animals. No less than 40% of their species are at some risk of extinction.

Deforestation, loss of habitat and the occurrence of diseases such as chytridiomycosis, which has devastated entire populations, were already more widely documented as threats, but now biologists are warning that rising temperatures, low humidity and drought, consequences of climate change, are further increasing the pressure on many amphibian species.

According to the study, from 2004-22, more than 300 species were brought very close to extinction, and 30% of these cases were mainly caused by the climate crisis.

“Water is essential for the reproduction of amphibians. It’s where they reproduce and tadpoles are born,” explains biologist Iberê Farina Machado, coordinator of the IUCN Species Survival Commission’s Assessment of Amphibians in Brazil and one of the article’s co-authors.

In addition, changes in temperature and humidity have an impact on their health and put their survival at risk. “Amphibians have moist skin and they breathe through it. Some species use a certain percentage of their lungs and another percentage of their skin for gas exchange, or vice versa. If the climate is too dry, this affects their breathing,” Machado adds.

Map produced by the survey reveals where the 2,873 species of amphibians threatened with extinction are located; the majority are in high-altitude areas, where there is less and less moisture available.

26 species possibly extinct in Brazil

Brazil is the country with the greatest amphibian diversity in the world, home to around 1,200 species. Almost a third of them have been assessed for the first time in this new report.

The assessment showed that 189 species are currently classified as critically endangered, endangered or vulnerable to extinction in Brazil. Furthermore, the most worrying aspect is that the vast majority of them are endemic.

“The scenario is even bleaker when we take into account the 26 species classified as possibly extinct, having not been sighted in natural environments since the 1980s or earlier,” Machado points out.

This is the case of the little warty frog (Holoaden bradei) and the Petropolis stone frog (Thoropa petropolitana), both of which were found in the Atlantic Forest in the last century. However, the last time the petropolitan was seen in the streams of the Rio de Janeiro hills was in 1982.

Nyctimantis pomba, a critically endangered species endemic to a single region in the Zona da Mata region of Minas Gerais, Brazil. Image courtesy of Diego José Santana/IUCN.

The biologist explains that in Brazil, deforestation and agricultural and urban expansion continue to be the main causes of amphibian extinction. However, climate change is increasingly present.

It is estimated that in the last 40 years, for example, the Amazon has become 1º Celsius (33.8º Fahrenheit) warmer and has seen a reduction in rainfall of up to 36% in some areas. Extreme droughts in the biome are increasingly recurrent. At this very moment, the Amazon states are experiencing one of the worst droughts in history. Rivers have dried up and navigation has been interrupted, leaving riverside populations without access to food and drinking water. More than a hundred dolphins have been found dead in Lake Tefé.

“As humans cause changes in climate and habitats, amphibians are unable to move very far to escape the increased frequency and intensity of extreme heat, forest fires, drought and hurricanes brought on by climate change,” says Jennifer Luedtke Swandby, coordinator of the Red List Authority of the IUCN Amphibian Specialist Group and one of those involved in the study.

Palawan horned toad (Megophrys ligayae), an endangered species endemic to the Philippines. Image courtesy of Robin Moore/Re:wild.

High-altitude amphibians are the most affected

Drought is synonymous with a lack of water and humidity. In this bleak scenario for the survival of amphibians, one would imagine that those that live closest to the ground would be the most impacted. However, this is not the case. Species that live in higher areas, more than 1,600 meters (5,250 feet) above sea level, perish more quickly.

In regions with large mountain ranges, such as Itatiaia National Park in Rio de Janeiro or Mount Roraima in the north of the country, toads, frogs, tree frogs and other amphibians suffer more from climatic disturbances.

“We’ve noticed the cloud lines getting higher and higher, which means there’s less moisture available for them at the top of the mountains. And since they can’t escape higher up, they end up becoming hostages to the climate,” says the Brazilian biologist.

On the left, a frog of the species Ghatophryne ornata, native to the Western Ghats mountain range in southern India. Image courtesy of Sandeep Das/IUCN. On the right, the crystal frog (Hyalinobatrachium aureoguttatum), which inhabits the forests of Ecuador, Colombia and Panama. Image courtesy of Robin Moore/Re:wild.

The loss of so many species and the possible imminent extinction of others are fresh reminders of the urgent need to contain the causes of climate change and mitigate its effects. Amphibians are important bioindicators of the health of their ecosystems and, consequently, of the planet.

“The warming world is losing many more species than human beings and they serve as a warning to us,” says Machado.

“Amphibians are disappearing faster than we can study them, but the list of reasons to protect them is long, including their role in medicine, pest control, alerting us to environmental conditions and making the planet more beautiful,” adds Kelsey Neam, species priorities and metrics coordinator at Re:wild and one of the study’s lead authors.

Citation:

Leudtke, J. A., Chanson, J., Neam, K., Hobin, L., Maciel, A. O., Catenazzi, A., … Stuart, S. N. (2023). Ongoing declines for the world’s amphibians in the face of emerging threats. Nature. Retrieved from https://www.nature.com/articles/s41586-023-06578-4

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This article by Suzana Camargo was first published by Mongabay.com. on 20 November 2023 | Translated by Carol de Marchi and André Cherri. Lead Image: Hyperolius substriatus, a frog native to Kenya and Tanzania, courtesy of Tim Davenport/Re:wild.