2% of World’s Amphibians Facing Overheating Threats Due to Climate Change: Study

Researchers have found that 104 of the 5,203 amphibian species they studied are already exposed to overheating in shaded terrestrial conditions, concluding that the pot is boiling for these 2 per cent of the species.

They expressed concern that a 4°C rise in global temperatures could push 7.5 per cent or 391 of the species studied beyond their physiological limits.

The study, published in Nature, said amphibians are vertebrates most at risk due to climate change, with over 40 per cent of amphibian species listed as being under threat. Thermal extremes may drive amphibians to extinction, according to the researchers.

Amphibians are ‘ectothermic’, meaning they can regulate body heat by external sources. They are also ‘area vulnerable’ to temperature change in their habitats.

The scientists estimated thermal limits for 60 per cent of the amphibian species (5,203), their daily operative body temperatures and their ability to tolerate extreme heat events in terrestrial, aquatic and arboreal microhabitats.

“All micro environmental projections assumed access to 85 per cent of shade and that amphibians had access to sufficient water to avoid desiccation in thermal refugia,” the study noted.

Patrice Pottier, post-doctoral researcher at University of New South Wales (UNSW), Sydney and lead author of the paper said in a statement, “It has previously been often assumed that species closer to the equator are at greater risk from overheating due to climate change than those in temperate regions.”

“However, our study found that tropical species in the Southern Hemisphere are the most impacted by overheating events, while non-tropical species are more impacted in the Northern Hemisphere,” he added.

Pottier said severity of heat impact varies as beyond 2°C warming, the impacts at 4°C increase disproportionately. This indicates that 2°C global warming could be a ‘tipping point’.

Though at current warming conditions, the shaded terrestrial species rarely experienced overheating events, under 4°C of warming, species are estimated to overheat on as many as 207.18 days, amounting up to 22.8 per cent of the warmest days of the year, the study said.

For arboreal species, these days are expected to be 76.17 under similar warming conditions.

The study also noted that most amphibians will not experience overheating events fully due to the presence of water bodies, allowing them to regulate their body temperatures below critical margins.

Only 11 species in most extreme warming events were analysed. “Our findings add to the growing evidence that finding access to cooler microhabitats is the main strategy that amphibians and other ectotherms can use to maintain sublethal body temperatures,” the study said.

Microhabitats such as shaded ground, aboveground vegetation and water bodies are assumed to be available across species’ range and they can maintain wet skin.

However, deforestation, urbanisation, shrinking shaded areas, droughts that may lead to evaporation of water bodies will have severe impacts on local humidity levels, habitat integrity and affect the ability of amphibians to regulate thermal temperatures.

“Consequently, amphibians will probably experience higher body temperatures and desiccation stress events than our models predict due to inconsistent access to cooler microhabitats, particularly in degraded systems,” the study observed.

The authors also said ectotherms could experience devastating effects of heat stress on their bodies even before reaching heat tolerant thresholds.

Prolonged exposure to high temperatures could impact their activity, disrupt phenology, reproductivity, fertility and death.

Droughts are known to impact frogs at such levels.

“Most species will not experience overheating events throughout their entire range, and these overheating events may not occur simultaneously. Thus, most species are likely to experience only local extirpation due to overheating, according to our models,” the study said.

Local extinctions could lead to change in ecology of the region such as eroding genetic diversity, impacting food chain and heath of ecosystem.