A new study from Penn State reveals that red-backed salamanders will be limited in their ability to adjust to climate warming in eastern North America in the coming decades. According to the researchers, the salamanders’ range will likely shift northward as temperatures rise.
Red-backed salamanders live in forests from Quebec south to North Carolina, and west to Missouri and Minnesota. For the investigation, the experts developed a new method to measure the metabolic rate of red-backed salamanders from different regions. They wanted to analyze how much more energy the salamanders would require to survive as temperatures rise.
Salamanders have evolved strategies to stay cool and preserve energy, such as burrowing under rocks and logs, explained study co-author Professor David Miller. But if the small amphibians must hide for extended periods to stay cool, they are not foraging or eating enough.
“Because these salamanders are ectotherms, cold-blooded animals, essentially what happens is when it is cold, they quit burning energy – as long as they don’t freeze, they can go long periods without food,” said Professor Miller. “Conversely, in the summer, when it’s really warm, their body temperature is elevated, and that raises how much energy they consume. So, during the warmest part of the year, if they’re not eating, they’re experiencing an energy deficit.”
Depending on greenhouse gas emissions, the global climate is very likely to warm by 2.16 to 3.42 degrees Fahrenheit from now to 2040, according to the United Nations. That will affect red-backed salamanders, said Miller, and may result in at least the southern end of their range moving northward.
“Ectotherms’ fitness is strongly governed by thermal conditions. Temperature directly impacts their ecology. Thermal conditions affect energy acquisition and allocation,” explained Professor Miller.
Lead researcher David Muñoz designed an innovative study to assess the energy expenditure of red-backed salamanders. The study was also designed to determine whether the salamanders’ metabolic rates varied in the warmer and cooler parts of their range.
The team collected salamanders from four populations near Richmond, Virginia; Millmont, Pennsylvania; Ithaca, New York; and Turners Falls, Massachusetts. The researchers captured 18 – 20 juveniles and 18 – 20 adult male salamanders at each site to look for life-stage differences.
Muñoz modified small refrigerators to serve as thermal chambers to subject the salamanders to warmer conditions. “Then the salamanders were placed in a small tube, and we measured how much oxygen was consumed by the salamander over two hours and how much carbon dioxide it emitted,” explained Muñoz. “We repeated the process multiple times, at different temperatures.”
The study revealed that salamanders from warmer climates lowered their metabolic rates to adjust to summer temperatures. This may act as an energy-saving mechanism during the warmest time of the year, the researchers suggested, adding that no such adjustability was evident in populations from cooler climates. They noted that both juvenile and adult salamanders exhibited metabolic “plasticity.”
Although some populations responded to historic climate thermal cues, said Professor Miller, no populations showed adjusted metabolic rate responses sufficient to deal with projected future climate temperatures, indicating there are constraints on salamanders’ responses to climate change.
According to Professor Miller, the research is important because predicted changes in global temperature are expected to increase extinction risk for ectotherms such as red-backed salamanders, primarily through increased metabolic rates. “We expect that warming will impact the energy budgets of salamanders, potentially affecting individual growth and reproductive success.”
The study is published in the journal Ecology and Evolution.