The critically endangered rough moss frog (Arthroleptella rugosa) only remains on one inselberg of indigenous fynbos amid invasive plants and wheatfields in South Africa.Credit: John Measey
The recently released second global review of amphibians (GAA2) considers the extinction risk of more than 8,000 species of frogs, salamanders and other amphibians based on 20 years of data collected and analysed by more than 1,000 experts.
According to an accompanying paper in Nature two out of every five amphibian species worldwide face extinction because of habitat destruction, diseases and, increasingly, climate change. Habitat destruction and degradation affects 93% of all threatened species.
GAA2 was coordinated by the Amphibian Red List Authority of the International Union for Conservation of Nature (IUCN) Species Survival Commission’s Amphibian Specialist Group, and hosted and managed by Re:wild.
John Measey of the Centre for Invasion Biology at Stellenbosch University and regional coordinator for southern Africa’s input into GAA2, describes such IUCN assessments as key indicators of the conservation status of regional amphibians.
According to the 2023 assessment, using data gathered between 2004 and 2022, there was no impact from climate change in the Afrotropics. GAA2 clarifies in a note that “the impacts of climate change on amphibians are poorly studied in this realm and likely underestimated.”
Status deteriorating
The latest report does, however, show that the number of Afrotropical and Palearctic species whose conservation status deteriorated because of disease increased from three to 11 species.
Measey says results from GAA2 indicate a lack of data, rather than meaning that there are fewer African species to be worried about compared to the rest of the world. This data gap reflects a lack of job opportunities for amphibian researchers in many countries, which makes regular comprehensive surveys difficult to complete. Many experts currently studying the continent’s species are not based at African institutions.
Herpetologist Mark-Oliver Rödel, a researcher at the Museum of Natural History in Berlin, Germany, and regional coordinator for West and Central Africa’s contribution to the recent global amphibian assessments who has studied amphibians across Africa and its islands for more than 30 years, says that except for southern Africa, not enough data is available on the continent’s species. He too blames this on the dearth of experts working on the continent.
“My estimate is that we only know of about half of Africa’s amphibian species,” he says.
GAA2 identifies the Afrotropics (which includes sub-Saharan Africa) as home to 1170 amphibian species. Most new species found over the past 20 years emerged from the forests of West and Central Africa and Madagascar. More than 175 new species have been described from Madagascar alone since 2006.
Increased disease
Rödel ascribes the increase in disease-related reports among western and eastern African amphibians to recent, intensified searches. He believes that possible disease related declines in Africa could still go unrecorded especially as known cases on the continent have mostly been identified by chance. He cites the example of Africa’s only known large-scale disease outbreak involving more than one population or species — in the mountains of western Cameroon.
A 2016 Plos ONE paper attributed it to chytridiomycosis, a disease induced by the pathogenic fungus Batrachochytrium dendrobatidis (Bd) which has had a devastating effect on populations worldwide. One of Rödel’s previous PhD students, Mareike Hirschfeld, noted its impact in Cameroon when she couldn’t find many of the frog species he had shown her on previous field trips. Puddle frog species (Phrynobatrachus) vanished completely from specific mountain tops, and populations of others dwindled. Several other species remained unharmed or even increased in numbers, perhaps due to competitive release, says Rödel.
“Because not all species disappeared, a naïve observer would think that everything is normal. In reality, many previously common species are gone. We only noticed it because we had very good data from the region before the population had crashed,” Rödel remembers.
Habitats at risk
“All species which depend on good, primary habitats of a special kind are threatened. I am worried for all species with narrow habitat preferences which only occur in small areas. If their habitat is primary rainforest or the top of mountains, their future is not bright,” he explains.
The rough moss frog (Arthroleptella rugosa) which is found on only one inselberg of indigenous fynbos amid invasive plants and wheatfields in South Africa, the Kinhansi spray toad (Nectophrynoides asperginis) which hasn’t lived in the wild since 2004 after a dam was built in Tanzania, the Mount Nimba reed frog (Hyperolius nimbae), whose remaining population in an Ivory Coast swamp, is threatened by increased human settlement, are all species counted among those at risk.
Measey, who primarily works in southern Africa, notes the impact of invasive trees and fish on indigenous amphibian species. A 2023 report from his lab in BioInvasion Records shows the impact of invasive fish such as bass feeding on the tadpoles of two South African ghost frog species. Overall, tadpole numbers are 18 times lower in streams where such invasive fish are present than in those without. In Austral Ecology, his team noted how invasive cluster pine trees impact the density of rough moss frogs (Arthroleptella rugosa) present on the sole stretch of its remaining Western Cape mountain habitat.
“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,” noted Kelsey Neam, Re:wild species priorities and metrics coordinator, and a lead author of the Nature paper.
“While our paper focuses on the effects of climate change on amphibians, the reverse is also critically important: that the protection and restoration of amphibians is a solution to the climate crisis because of their key role in keeping carbon-storing ecosystems healthy.”
