By Jake Eig
New Orleans has been a world-famous attraction for hundreds of years, but it is not just tourists on Bourbon street that have flocked to the city. Over the past 150 years, New Orleans has experienced a massive influx of Brown Anole lizards. The Brown Anoles have imposed themselves in the same habitat as the native Green Anoles, displacing the more vibrant lizards. Experts believe that the Brown Anole is an invasive species, and the impact of their presence is only just being realized.
Perhaps no creature has been more abundant in Louisiana than the Green Anole lizard, but recently they have become harder and harder to locate. I spoke with herpetologist Dr. Alexander Gunderson at Tulane University about the anole population in New Orleans, hoping to find out where the lovely green lizards had gone.
“The green species is native,” Gunderson said. “It’s been here for millions of years.”
Louisiana is just far enough south to be able to support reptile life, and the green lizards have been here much longer than any people.
“New Orleans is in a subtropical climate, so it’s relatively warm most of the time,” said Gunderson. “Most species of reptiles live in the tropics. So, we are in a zone that is pretty suitable for a lot of species.”
But, over the last century, the population of Green Anoles is seemingly dropping due to the emergence of the Brown Anole.
“The Brown ones, the Anolis Sagrei, are native to Cuba and the Bahamas. They were introduced to North America sometime in the last 150 years. They’ve been spreading across the country, starting in Florida and now they are in Georgia.”
The Brown Anoles likely came over in potted plants. Dr. Gunderson explained the evolutionary differences between the green and brown species.
“They are separated by 40 million years of evolutionary convergence,” he said. “They are in the same genus but not closely related to one another.”
While not closely related, they share many of the same tendencies which can lead to a tragedy of the commons.
“They eat the same things,” Dr. Gunderson said. “They hang out in the same places.”
Many experts are noticing an exponential growth in the number of Brown Anoles, invading the habitat of the ancient Green Anole.
“Even 20 years ago there weren’t very many Brown Anoles in New Orleans, it’s been a steady increase in the numbers over time.”
So, what is causing this increase in the Brown Anole population? One common theory is that the Brown Anole lays more eggs than the Green Anole. Further, the Brown Anoles have displaced the surviving Green Anoles.
“Especially in cities, the brown species is displacing the green species,” said Gunderson. “The green species is becoming less common, and when they do co-occur, the green species moves to a different part of the habitat. So, they used to be close to the ground on tree trunks and now they are up in the canopy. They are being run out.”
Still, there is much debate over the actual invasive ability of the Brown Anoles. Despite staking a claim on New Orleans, the rest of the state still has Green Anoles galore.
“The pattern is different in cities versus outside of cities. In cities, the Brown Anole is outcompeting the green anole,” Gunderson said. “But, if you go outside the city the green anole is in many cases the only one there. Brown anoles do better in cities”
While many experts would suggest that the Brown Anoles have a higher tolerance to cold weather, Dr. Gunderson’s research team has discovered that this is not the case.
“Actually, they can’t handle temperatures that get more extreme which was surprising to us. We thought that since they are doing so well, maybe they have a higher tolerance for cold,” he said. “Our initial evidence suggests that the green anole can tolerate lower temperatures.”
Despite all of the experts analyzing the situation, it is still not entirely clear why the Green lizards seem to be vanishing.
“We don’t fully understand why this is happening,” said Dr. Gunderson. “But, we know that Brown Anole lizards are an invasive species displacing the Green Anoles.”
While the Green Anole might not be dying out, they are surely being run out of town by the new lizards on the block.