/ 10 October 2023

Frogs are sliding towards extinction

Two out of every five species of amphibians — frogs, salamanders and caecilians (which resemble large worms) — are in danger of vanishing forever, a new global assessment has found

“Our little froggies are essentially going to be drying up and turning into little pieces of biltong”

Two out of every five species of amphibians — frogs, salamanders and caecilians (which resemble large worms) — are in danger of vanishing forever, a new global assessment has found.

A staggering 41% of the 8 011 amphibian species worldwide are threatened with extinction, making them the most threatened vertebrate group, according to the findings of the second Global Amphibian Assessment

This is compared to 26.5% of mammals, 21.4% of reptiles and 12.9% of birds. Salamanders are at particularly high risk of extinction, with 60% of species threatened.

The assessment was coordinated by the Amphibian Red List Authority, a branch of the International Union for Conservation of Nature’s (IUCN’s) Species Survival Commission’s Amphibian Specialist Group, which is hosted and managed by Re:wild

“The state of the world’s amphibians is more dire today than at the time of the first Global Amphibian Assessment in 2004,” the report said. 

“Habitat loss and degradation remains a threat to almost all threatened amphibians, while disease continues to spread across the globe, with a new variant targeting salamanders of increasing concern.” 

The emerging and “intricate threat” of climate change highlights the urgent need for research and piloting interventions to gain a better understanding of the problems and solutions “before it is too late”.

Amphibians, found on every continent except Antarctica, have evolved into an incredible diversity of sizes, colours and behaviours, and can be as tiny as a common housefly and as long as a cow. 

“Some resemble multi-colored jewels scattered on the forest floor, while others are masters of camouflage, mimicking tree bark or leaf-litter. There are amphibians that can glide through the air and others that spend nearly their entire lives underground,” the report said.

Rising extinctions

But they “are disappearing faster than we can study them”, with the report noting how amphibian extinctions continue to rise. There were 23 extinctions by 1980, an additional 10 by 2004 and four more by 2022. 

The number of amphibian extinctions could be as high as 222, “when considering the 37 confirmed extinctions and an additional 185 species with no known surviving population”. 

Habitat loss and degradation remains the top threat, affecting 93% of threatened species. “A rapidly growing human population and unsustainable consumerism continues to drive deforestation, agricultural expansion, infrastructure development, energy production, and pollution, leaving amphibians with fewer places to live, breed, and feed.”

The report cited the case of the Itombwe Highlands in the Democratic Republic of the Congo, known for its rich mineral deposits and biodiversity. “Artisanal mining is rampant and more recently, there has been a notable upsurge in semi-industrial gold mining activities occurring at the fringes of and within protected areas.” 

The associated detrimental effects of deforestation, water pollution, soil erosion and violent conflict have threatened locals and the region’s biodiversity, including the endangered Itombwe golden frog and Kabembe treefrog, it said.

Climate change a big threat

Amphibians are ectotherms (cold-blooded) with moist, highly permeable skin and rely on the availability of water for survival. These attributes render them particularly sensitive to changes in humidity and temperature, as well as other environmental shifts related to climate change. 

“With further predicted changes in temperature and humidity, the extent and severity of this threat are expected to magnify in the future,” the report said.

Last week, a new paper in Nature, based on the assessment, found that climate change is emerging as one of the biggest threats to frogs, salamanders and caecilians. From 2004 to 2022, a few critical threats have pushed more than 300 amphibians closer to extinction, with climate change the primary threat for 39% of these species. 

This figure is expected to rise as better data and projections on species’ responses to climate change become available. Habitat destruction and degradation, disease, and overexploitation are all threats that are exacerbated by the effects of climate change, the researchers said.

“IUCN assessments are a key indicator to the conservation status of our regional amphibians and this assessment demonstrates their ongoing decline,” said John Measey of Stellenbosch University’s Centre for Invasion Biology, who was among more than 100 international experts who contributed to the study. He was responsible for the Southern African part of the project. 

“This study shows hotspots of disease in central and eastern African amphibians as an emerging concern for their conservation on the continent,” Measey said, adding that the Red List Index suggests the ongoing decline of African amphibians is primarily driven by habitat loss, but most recently by disease.

Disease, invasive species

Chytridiomycosis, a disease that affects the function of amphibian skin and is caused by the chytrid fungus Batrachochytrium dendrobatidis, has been implicated in amphibian declines worldwide and is the suspected cause of nine of the 11 documented extinctions since the 1980s. The emergence of Batrachochytrium salamandrivorans (Bsal) in Europe is “particularly concerning for salamanders”.

Fires, both natural or human-caused, can cause habitat loss and degradation, as well as direct mortality. “The combination of climate change and deforestation has led to hotter and drier weather patterns, thus more frequent and intense fires, making it difficult for populations to recover.”

Many invasive species can outcompete native amphibians for resources or prey on them directly, the report noted. “For example, non-native fish can prey on amphibian eggs and tadpoles, while invasive plants can modify the habitat available to amphibians, leading to population declines.”

Overexploitation and unsustainable trade practices have put significant pressure on many species of amphibians. Some are harvested for food or traditional medicine, while others are collected for the pet trade because of their uniqueness or beautiful colouration.”

‘Frogs don’t win’

Jeanne Tarrant, who runs the threatened amphibian programme at the Endangered Wildlife Trust, pointed out that “if our amphibians are in trouble, it means our freshwater and the environments that supply us with everything we need to live, are in trouble too”. 

In South Africa, frogs are the only kind of amphibians the country has, and habitat loss remains a significant driver of their declines. 

“Literally, we see it every day — the incremental loss of habitat — and even when it’s legally done, all following the due process, our frogs don’t win. Slowly, surely we’re just eating away at all this habitat whether it’s wetlands, grasslands, forests, all being chewed up by the human footprint.” 

Drying out

Climate change is an emerging threat. “Most of our threatened species are montane species; they live on mountains, and are very isolated so one species per mountain range and with climate change, there’s going to be shifts in the hydrological cycle.”

This may include decreased mist cover, decreased rainfall, more drying, increased incidence of UV “especially at these high altitudes”, and Tarrant said all of these factors directly affect the development stages of frogs.

“Just in terms of frogs’ physiology, their skin is such an important organ to them. They have to be moist all the time so that’s why they’re mostly active at night, and are generally associated with water, or if not, in leaf litter or under the soil. So, if it’s very hot, which we’re seeing, with this gradual increase in temperature, our little froggies are essentially going to be drying up and turning into little pieces of biltong.”

The report noted that since 1980, the extinction risk of 63 species has been reduced because of conservation interventions, proving that conservation works. “We must build on this momentum and significantly scale-up investment in amphibian conservation if we are to stop and reverse declines,” it said.

Tarrant agreed. “We’ve got evidence to show that conservation does work and we really need to protect habitats and manage them and keep what we’ve still got left intact. 

“It feels like there’s still a lot of opportunity to do that for amphibians in South Africa and on the African continent. We need all the help we can get in doing that and showcasing that these are such cool interesting animals,” she said.  

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