Article by Morgan Erickson-Davis.
Rising temperatures and drying air pose problems for plants and animals around the planet. Amphibians, with their permeable skin and inability to travel far, are considered to be among the most vulnerable to global warming. But new research published yesterday in Science Advances provides a bit of hope, finding salamanders in eastern North America may be able to cope with a changing world better than scientists previously assumed.
North America is the world’s salamander diversity hotspot, home to nearly half of all species on the planet. The Appalachian Mountains in the eastern U.S. and Canada is a hotspot within this hotspot, containing around 10 percent of the world’s species. Scientists think the region is home to so many because it is there, in small mountain streams, where the most-diverse salamander family – Plethodontidae – first evolved millions of years ago.
Today, salamanders are so plentiful that they are likely the most abundant vertebratesin North American forests. Scientists think there are so many salamanders in the southern Appalachians that the mass of those that live in just one square mile of forest would together likely weigh between 2,500 and 5,000 pounds. That’s a lot of salamanders, considering many of them have about as much heft as a teaspoon of sugar.
“On the nights when I was surveying for salamanders, I could look down and find them sitting on top of my boots. I had to pay special attention to every step I took,” said Eric Riddell, a biologist currently at the University of California at Berkeley. “Some of our best estimates suggest that salamanders outweigh all other vertebrates in the forest. If you put all the bears on one side of a scale and all the salamanders on the other, the salamanders would weigh more.”
But someone going for a day hike in one of these forests would be hard pressed to see even one. That’s because salamanders are most active in the cool and damp of the night, preferring to while away sunny hours under leaf litter and rotting logs.
“Most people don’t realize how abundant salamanders are because people don’t do much hiking in the dark,” Riddel said.
Their sheer numbers mean that salamanders play a big role in forest ecosystems, both as predators and prey. They provide an important regulatory mechanism for insects and other invertebrates that live on the forest floor. Many of these invertebrates eat fallen leaves and other plant matter, which releases the CO2 they contain into the atmosphere. In eating these invertebrates, salamanders allow more plant matter – and the carbon it contains – to be buried in the soil, keeping greenhouse gases out of the atmosphere. And it’s no small amount; according to a 2014 study, just one species of salamander is keeping more than 72 metric tons of carbon out of the atmosphere every year.
But along with the rest of the world, the Appalachians are changing as human-caused greenhouse gas emissions warm up the planet. And when air gets hotter, it gets dryer – which could be a big problem for moist-skinned amphibians like salamanders.
Previous research has predicted dire futures for eastern U.S. salamanders as climate change shrinks their habitat. But no study had taken into account the ability of salamanders to acclimate to new conditions. So Riddell and a team of other researchers at Clemson University in South Carolina set out to see how much of a difference this might make.
They looked at red-cheeked salamanders (Plethodon jordani), which are among the most common salamanders in southern Appalachia and which live in habitats at a variety of elevations.
Like other plethodontids, red-cheeked salamanders (Plethodon jordani) don’t have lungs. Instead, they breathe through their skin. Photo by Brian Stansberry via Wikimedia Commons (CC BY-SA 3.0)
Riddell said that when he and his colleagues examined their responses to increased temperatures and dryness, they discovered that these salamanders “have some tricks up their sleeves” that help them deal with less-than-ideal conditions.
For one, salamanders were able to increase their resistance to water loss by up to 68 percent when air became drier. They can also lower their metabolic rate by nearly 25 percent as temperatures rise, allowing them to get away with eating less and thereby lowering their exposure to the outside environment.
Overall, the researchers found that these physiological and behavioral acclimation abilities – termed “plasticity” – may reduce Appalachian salamander extinction risk by up to 72 percent.
“This is one of the first papers that has exclusively looked at plasticity in this sense. We’re telling you that our new predictions are nowhere near as dire as earlier predictions. In this part of the world, this is a particularly big deal,” said Michael Sears, an associate professor in the department of biological sciences at Clemson University and coauthor of the study. “We can now say more accurately what might occur if climatic conditions continue to deteriorate.”
However, the study reveals that not all salamanders are endowed equally when it comes to plasticity, with smaller ones less able to acclimate to warmer, drier conditions. Riddell, Sears and their colleagues write that this is “likely due to their low surface area–to–volume ratios, higher energy intake, and greater [fat] reserves that minimize the risk of starvation.”
The researchers say their results show that the acclimatization ability of wildlife is an important part of the puzzle of how ecosystems will react to climate change, and “underscores the need to include complex biological responses, such as plasticity and adaptation, into ecological predictions of climate change.” They say it could also be used to improve conservation planning.
Additionally, the study may shed light on how salamanders have successfully persisted in the Appalachians for so long despite some previous big (albeit slower) climatic upheavals over the past millions of years.
“This suggests to me that these organisms hunker down and essentially shelter in place in the face of changing climates,” said David Wake, one of one of the world’s leading experts on salamander diversity.
“In short, they are able to adjust their physiology much more than we previously thought, and this perhaps accounts for much of their ability to deal with climate change – not by running away, but by using their abilities to adjust through time.”
Citation: Eric A. Riddell, Jonathan P. Odom, Jason D. Damm and Michael W. Sears. Plasticity reveals hidden resistance to extinction under climate change in the global hotspot of salamander diversity. Sci Adv 4 (7), eaar5471.
Banner image: A Cukra climbing salamander (Bolitoglossa striatula) in Costa Rica.