Invasive species can dramatically reshape environments and cause extinction, even when they don’t prey on their newfound neighbours, according to new research that highlights the dangers of altering habitats.
The six-year study of lizards on a string of remote islands found that the arrival of a predator can prompt species that previously co-existed peacefully to cluster in a shared refuge, creating competition that can be devastating.
It challenges a long-standing theory that predators feeding on animals lower down the food chain prevent any one prey species from dominating a habitat, and so promote ecological diversity.
“Our results suggest that we need to update conventional wisdom in a few ways,” said lead author Robert Pringle, associate professor of ecology and evolutionary biology at Princeton University.
“We need to think about unexpected indirect impacts — the species at greatest risk of extinction might not necessarily be those with the greatest risk of being eaten,” he told AFP.
– A blank canvas –
Understanding how species co-exist is one of the biggest challenges in biology, not least because it is hard to find or create control environments for experimentation.
But Pringle and his team found a solution in the form of a string of 16 islands in the Caribbean, home to an unassuming lizard known as the brown anole, which largely hunts on the ground and in low branches.
The islands provided the researchers with the perfect blank canvas to observe how the native brown anole population would react when different invasive species were introduced.
They examined four scenarios: a control group of islands where the native population was left alone, a group where the competitor tree-dwelling green anole was introduced, a group where a top predator called a curly-tailed lizard was introduced, and a group where both new species joined the native brown anoles.
The first test was to see if the ground-hunting brown and tree-dwelling green anoles could co-exist successfully.
The study found that was possible: the green anoles rapidly multiplied, and while the brown anole population didn’t grow as much as on the control islands, it still expanded.
The introduction of the curly-tailed predator lizard — a ground-dweller that can eat both the unfortunate brown anole and its prey — saw the native population change behaviour.
Brown anoles took to the trees, leaving behind much of their usual hunting grounds to stay beyond the reach of the new arrivals. This meant the brown anole population did not grow, but the native lizard at least remained static.
– ‘Landscape of fear’ –
But the most interesting results of the research, published Thursday in the journal Nature, came from the final scenario, where all three lizards were forced to share the same habitat.
Under the existing theory, the curly-tailed lizard should have prevented either of the anoles from dominating and detente would have prevailed.
But in fact, brown anoles moved up into the trees to escape the predators and found themselves in competition with the green anoles, with dire results.
The brown anole population shrank more than 40 percent, and on two of the islands the green anoles went extinct. On a third their population was static and only on one did they grow moderately.
The population collapses came despite the fact that the curly-tailed lizards were rarely eating the anoles — they were effectively driving themselves into extinction.
“The ‘landscape of fear’ created by the predator forces prey species into intense competition,” Pringle said.
“Introducing a predatory species can cause the extinction of prey species that never even encounter the predator.”
The research leaves some questions unanswered, including why the green anoles suffered more than the brown anoles in their refuge from the curly tailed predators.
And the islands have more to offer: having documented how brown anoles altered their habitat and diet to escape predators, the researchers now want to examine what evolutionary shifts these changes may have caused in the species.
Democratic candidates demand investigation into toxic culture at NBC ahead of MSNBC debate
Sens. Elizabeth Warren of Massachusetts, Bernie Sanders of Vermont, Kamala Harris of California and Cory Booker of New Jersey signed a letter calling the allegations of “sexual assault and harassment” by employees and “a cover-up by NBC’s management” deeply “troubling.” Instead of addressing the company, the senators issued their letter to Democratic National Committee chairman Tom Perez.
Revealed: Nikki Haley sent confidential information about North Korea nuke scare over system meant only for unclassified communications
"Convenience is not an acceptable reason to skirt information security rules. She should be held to the same standard as everyone else," said Austin Evers, executive director at American Oversight, upon hearing the news that former UN ambassador Nikki Haley used a Blackberry smartphone to communicate with staff regarding North Korea's July, 2017 test of an intercontinental ballistic missile that could hit the US.
Fox News commentator Sean Hannity appears to be knee-deep in Trump’s Ukraine scandal — despite his denials
Fox News host Sean Hannity raved that he never spoke with Secretary of State Mike Pompeo about ousted Ukrainian Ambassador Marie Yovanovitch after a third witness confirmed the alleged call to impeachment investigators.
David Hale, the undersecretary of State for political affairs, testified under oath that Yovanovitch was the victim of a baseless smear campaign led by Rudy Giuliani, the personal attorney of President Donald Trump, which led to her ouster. According to a transcript of the closed-door deposition released Monday, the smears originally stemmed from the conservative columnist John Solomon, who wrote in The Hill that former Ukrainian Prosecutor General Yuriy Lutsenko had claimed that Yovanovitch gave him a “do not prosecute list.” Lutsenko later retracted that claim.