Mr. Yuan ventured to the Izu Islands with a tripod and a makeshift racetrack strapped on his back. After catching lizards on Kozu, an island with snakes, as well as the snake- and weasel-free Hachijo-Kojima, Mr. Yuan recorded the lizards running along the track with a camera to calculate their running speeds at different body temperatures.
Lizards and snakes are both ectotherms, meaning that their body temperatures depend on their surrounding thermal environment. Body temperature, in turn, affects their ability to move; immobile at cold temperatures, their movement speed increases as they warm up, before reaching a plateau and rapidly declining when it gets too hot.
The researchers found that the lizards on the islands with snakes were running faster at higher temperatures, suggesting that they were more adapted to warmer body temperatures, Mr. Yuan said. At these higher body temperatures, the lizards sprinted faster than the snakes could crawl.
The presence of predators also had evolutionary effects on the lizards’ bodies; lizards on islands with snakes had longer hind legs.
“We’re essentially linking the presence of the snakes to the lizards running faster, those lizards having longer legs and those lizards foraging at warmer body temperatures,” Mr. Yuan, the study’s lead author, said.
The data collected for the study also highlighted another serendipitous, if worrying, finding. The Izu Islands have only gotten warmer since Dr. Hasegawa first set foot there, and so have the lizards. From 1981 to 2019, the average lizard body temperature rose 2.3 degrees Fahrenheit across all the islands, correlating with climatic warming.
Rising temperatures may threaten ectotherms, which comprise the majority of animal species, and alter the dynamics of prey-predator relationships, said Shane Campbell-Staton, an evolutionary biologist at the University of California, Los Angeles, who was not involved in the study.