By Morgan Spehar
Don Miles described standing in front of the coffee-drinking crowd at Front Room as, “a little like being a Costco salesperson,” because of the tiny microphone hooked around his ear that allowed him to speak up over the sounds of beans being ground and drinks being poured. But he wasn’t there to talk about the $1.50 hotdog.
Miles, a biology professor at Ohio University, spoke at the OHIO Science Cafe series about lizards and how the four-legged reptiles are going to be affected by a warming planet, a topic which he has been researching for 20 years.
He explained to the full cafe that lizards are ectotherms, which means that they get their heat through their environment, mostly from the sun (in contrast, humans are endotherms, which means we can regulate our own internal temperatures). Because they rely on the environment to maintain their body temperature, ectotherms are particularly sensitive to changes in climate.
When Miles noticed that some of the lizards that he normally studied in southern North America and other areas were disappearing, he began conducting research to try to find the link between climate change and lizard extinctions. He used copper lizard models to measure the body temperatures of the reptiles (Tb) and the maximum temperature that the lizards could handle (Tmax).
“We measured something called [the lizards’] operative environmental temperature,” he said. “So we made these models and we deployed them in the environment where the lizards were still present and where the lizards were absent…We were seeing in areas where Tmax was above Tb lizards were going extinct.”
Due to the rising temperatures that are a direct result of climate change, the lizards were being forced to live in environments above their thermal maximum (Tmax), which caused them to die. But overheating isn’t the only threat that lizard populations face because of the global rise in temperatures.
Some lizards are viviparous, which means they give live birth, while others are oviparous, meaning the young lizards hatch from eggs. For female viviparous lizards, maintaining body temperature is especially important because overheating could create developmental issues with the baby in the womb or could cause a female to not reproduce at all.
These consequences make the estimated changes in temperature even more concerning.
“Rises in temperatures were most severe in January to May,” Miles said, “which is the period when viviparous females are holding young in their womb, which is deleterious for reproduction.”
Lizards that cannot use behavior to help regulate their temperature (such as digging burrows to create a cooler air temperature) or that live in environments where the temperature is already close to their thermal maximum are even more vulnerable. Miles predicted that 20 percent of lizard species would go extinct by 2080.
“The problematic thing is that these extinction spasms occur in the areas of the world that have the richest reptile diversities,” he said, pointing out that the number of species of lizards living on Earth would take a severe blow.
Habitat loss and fragmentation, along with heatwaves, droughts and fires, mean the future for lizards is looking a little grim. But Miles hasn’t lost hope.
“Are they any reasons to be optimistic? I think yeah,” he said. “[Especially] if we look at species that can use behavior to evade the warming.”
For example, in a paper he published in 2017, Miles, along with several others, noted that some lizard species were shifting their territory to higher altitudes when available, allowing them to survive the warmer temperatures.
As climate change continues to make the planet warmer and people continue to dump CO2 into the atmosphere, lizards must either adapt or go extinct. Obviously, lizards are not the only group of organisms that are threatened by climate change. For many species, behavioral changes could mean the difference between surviving to reproduce and extinction, which would result in an incredible loss of biodiversity.
Click here for Don Miles’ full Science Cafe Lecture.