Mr. Yuan ventured to the Izu Islands with a tripod and a temporary racetrack on his back. After catching lizards on Kozu, an island with snakes, as well as the snake- and orphan-free Hachijo-Kojima, Mr. Yuan recorded the lizards running with the camera along the track to calculate their running speed at different body temperatures.
Lizards and snakes are both ectotherms, meaning their body temperature depends on their surrounding thermal environment. Body temperature in turn affects their ability to move; immobile at cold temperatures, increases their speed of movement as they warm up, before reaching a plateau and decreasing rapidly when it gets too hot..
The researchers found that the lizards on the islands with snakes run faster at higher temperatures, indicating that they are more adapted to warmer body temperatures, said Mr. Yuan said. At these higher body temperatures, the lizards jumped faster than the snakes could crawl.
The presence of predators also had evolutionary effects on the bodies of lizards; lizards on islands with snakes had longer hind legs.
“We actually link the presence of snakes to the lizards that run faster. The lizards have longer legs and the lizards that seek at warmer body temperatures,” said Yuan, the study’s lead author.
The data collected for the study also highlighted another satisfactory, if worrying finding. The Izu Islands have only gotten warmer since Dr. Hasegawa first set foot there, and so did the lizards. From 1981 to 2019, the body temperature of the lizard on all the islands rose by 2.3 degrees Fahrenheit, which correlates with climate warming.
Rising temperatures could threaten ectotherms, which contain most animal species, and alter the dynamics of prey-predator ratios, says Shane Campbell-Staton, an evolutionary biologist at the University of California, Los Angeles, who was not involved in the study.