Amphibians are being pushed beyond their heat limits

A recent study offers a clearer picture of which amphibians and habitats face the greatest threat from rising temperatures. 

Amphibians are notably fragile in a warming world due to their dependence on external sources to regulate body heat, with more than 40% of species already classified as endangered. As entire populations vanish, the ripple effects throughout ecosystems could be devastating.

“We wanted to better understand the risk climate change poses to amphibians, and so put together the most comprehensive compilation of heat tolerance limits to date,” said lead author Patrice Pottier, a postdoctoral fellow at UNSW.

Heat tolerance limits of amphibians 

Amphibians, being ectotherms, cannot generate enough internal heat on their own and therefore depend on the environment to maintain suitable body temperatures. 

Given how little data existed on their ability to endure higher heat levels, the UNSW team aggregated thousands of measurements, representing hundreds of species.

“Heat tolerance limits are the maximum temperature amphibians can tolerate before their physiological systems fail,” Pottier said.

The experts applied a statistical method called data imputation to estimate values for species that have not been directly studied.

“In this case, it predicts heat tolerance limits for species we do not have data for by looking at how heat tolerance is linked to factors like habitat type, environmental temperature, and evolutionary history,” Pottier explained.

By doing so, the scientists developed a comprehensive catalog of heat thresholds covering about 60% of all known amphibian species. This overview highlights where warming poses the greatest risk and which animals might be most vulnerable to local extinctions.

Amphibians are already under strain

The research team examined the environmental conditions amphibians encounter in different microhabitats – on land, in trees, or in water – and then compared these conditions to each species’ calculated heat tolerance limits. 

“We found that 104 out of 5,203 species – 2% – are already exposed to overheating in shaded terrestrial conditions. And a 4°C global temperature increase could push 7.5% of species beyond their physiological limits,” Pottier said.

The experts also discovered that the areas most at risk do not necessarily line up with latitude alone, a finding that revises earlier assumptions.

“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,” Pottier explained.

As a result, relying on a one-size-fits-all pattern like latitude to assess threats may overlook specific places and species already pushing against their tolerable heat boundaries.

“Assuming that all tropical species are more vulnerable than temperate species can be misleading. What matters is assessing if the area is going to experience extreme heat events relative to the species’ heat tolerance. This requires stepping away from general trends, and identifying specific areas and species at risk,” Pottier added.

Escalating impacts with greater warming 

The scientists modeled how conditions might worsen under different global warming scenarios. Even at 2°C above pre-industrial levels, more amphibians are likely to face critical heat exposure. But surpassing that threshold would be especially dangerous.

“Impacts escalate under different climate warming scenarios. There is an increase in impact between the current climate and +2C of warming; but impacts increase disproportionally under +4C of warming. This step-change impact severity shows that going above +2C of global warming can be a tipping point where we may see a lot of local extinctions,” Pottier noted.

Local disappearances carry additional risks: losing these frogs, salamanders, and toads can disrupt food webs, hamper insect control, and reduce overall genetic diversity in local ecosystems.

“Some amphibian populations may undergo range shifts to more hospitable habitats, but opportunities for this are likely limited due to low dispersal rates and reliance on water bodies,” Pottier added.

Ecological and cultural significance

Amphibians are not just vital for pest management and as a food source for predators; they are also intertwined with human cultures around the globe.

Pottier pointed out that amphibians are an important part of the ecosystem. For example, the loss of an amphibian population would likely lead to an increase in insect population with carry-over effects on plants and animals, he noted.

“They are prey for many animals and their loss would have knock-on effects on many other species. Besides ecosystem impacts, amphibians are deeply rooted in human cultures and it would be a shame to lose such beautiful and emblematic species.”

Mitigating heat impacts on amphibians 

The findings emphasize the importance of microhabitats that moderate temperature extremes. Places with plenty of foliage and accessible water sources can help amphibians survive short-term heat spikes by letting them cool off and keep their skin moist.

“Our analyses made it clear that vegetation and water bodies are critical in buffering amphibians during heat waves. We found that if you provide amphibians with enough water and enough shade, a lot of them can survive extreme heat events. We must protect and restore the environments that allow them to regulate their body temperature,” Pottier stressed.

Because the study assumed best-case scenarios for shade and moisture, actual threats could exceed even these concerning estimates.

“We used very conservative estimates in this study assuming access to cool shaded environments. Therefore, the impacts of global warming will likely exceed our projections. So all efforts to limit global warming are needed to protect the world’s amphibians,” he concluded.

Overall, this large-scale analysis highlights both the fragility of amphibian populations under climate stress and the steps that can help them cope – namely, curbing global temperatures and safeguarding vital habitats with adequate cover and water.

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