When European explorers arrived in the Caribbean 500 years ago, they didn’t just upend the lives of the Indigenous people they encountered—they altered the entire ecosystem. As many as 70% of the snakes and lizards living on some islands may have vanished, a new study suggests. And it wasn’t just the colonists that were responsible: It was the cats, rats, and raccoons they brought with them.
The findings suggest it’s not humans, per se, that cause problems for vulnerable species, but, “We see very different effects” depending on how those humans interact with their environment, says Erle Ellis, a geographer at the University of Maryland, Baltimore County, who was not involved with the work. The new results, he adds, are “critical” to future conservation efforts.
Scientists know little about where lizards, snakes, and other reptiles live, compared with popular animals like panda bears. They know even less about the ancient history of these animals. Yet there’s a growing realization that these species play key roles in their ecosystems: They pollinate plants, disperse seeds, eat small animals like insects, and are themselves eaten by even bigger animals. Some even change the very landscape by burrowing into the earth.
So Corentin Bochaton, a zooarchaeologist at the Max Planck Institute for the Science of Human History, headed to the biodiversity hot spot of the Caribbean. He and his colleagues visited previously excavated caves on six islands in Guadeloupe, a set of islands governed by France in the eastern Caribbean. After sifting through the dirt in different layers of the cave floors and going through the findings of the previous excavations, they collected tens of thousands of bone fragments, some as small as 3 millimeters.
Among the 43,000 fossils unearthed, the researchers identified 16 distinct types of lizards and snakes. They divided their fossils into four groups: those 32,000 to 11,000 years old, those 11,650 to 2540 years old, those 2450 to 458 years old (a period after the island’s Indigenous inhabitants arrived, but before European explorers did), and those dating from 458 years ago to the present.
One island hosted at least four types of snakes and five types of lizards 11,000 years ago, none of which exist there today, the team reports today in Science Advances. They were eventually replaced by four other species of lizard, two of which made their first appearance about 2000 years ago, and two of which arrived after the Europeans. Those new species most likely came from other parts of the Caribbean.
Bochaton and his colleagues next traced the evolutionary history of snakes and lizards in Guadeloupe for the past 40,000 years. At least 13 reptile species thrived before the arrival of Christopher Columbus in 1493, they found, spread among at least 76 populations. For thousands of years, neither climate change nor the presence of Indigenous people proved to be a problem.
But roughly half those populations disappeared within 350 years of European settlement, and at least three snake and five lizard species went extinct. Some islands lost up to 70% of their reptile species. The lizards were likely victims of invasive animals that arrived with the Europeans, such as mongoose and cats, or died out after losing their habitat to sugar cane fields and grazing, the researchers say. Iguanas and five other newly arrived lizards took their place. Bochaton says the pattern has likely repeated itself across other islands in the Caribbean.
It’s not clear what those losses meant for island ecosystems, but the findings are a little unsettling, says Jonathan Losos, an evolutionary ecologist at Washington University in St. Louis who was not involved with the new work. That’s because he and other scientists have spent much of their careers studying the interplay between ecology and evolution in the reptiles that live throughout today’s Caribbean. “What [is] there today has only been around for a few centuries,” he explains. “We have a very biased view,” given the relatively short histories of some of these animals in the region.
The results also bolster a growing theory among scientists: that biodiversity can continue to exist alongside humans when they manage the land with sustainable practices common among Indigenous people, Ellis says. “It’s backing up the narrative people are seeing over the world.”
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