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.
WATCH: Franklin Graham tells Jeanine Pirro coronavirus pandemic is because of people sinning
Franklin Graham blamed sinners for the COVID-19 coronavirus epidemic during a Saturday night appearance on Fox News.
Host Jeanine Pirro noted the growing death toll and wondered how God could let that happen.
"Well, I don't think it's God's plan for this to happen," Graham said.
"It's because of the sin that's in the world, judge," he argued.
"Man has turned his back on God, we have sinned against him, and we need to ask for God's forgiveness and that's what Easter's all about," he continued.
"This pandemic, this is the result of a fallen world that has turned its back on God," he added.
Drought causing water shortage amid coronavirus crisis in Chile
With historically low river flows and reservoirs running dry due to drought, people in central Chile have found themselves particularly vulnerable to the coronavirus pandemic.
Years of resource exploitation and lax legislation have allowed most reservoirs in that part of the country to run dry.
"There are now 400,000 families, nearly 1.5 million people approximately, whose supply of 50 liters of water a day depends on tankers," Rodrigo Mundaca, spokesman for the Movement for the Defense of Water, the Earth and the Protection of the Environment, told AFP.
One of the main pieces of advice to protect people against coronavirus is to wash your hands regularly.
Trump warns of ‘tough week’ ahead — after the United States surpassed 300,000 coronavirus victims
US President Donald Trump warned Americans on Saturday to brace for a "very horrendous" number of coronavirus deaths in the coming days as the total number of global fatalities from the pandemic soared past 60,000.
As confirmed COVID-19 cases in the United States surpassed 300,000 with more than 8,300 deaths, there was some encouraging news in Italy and Spain.
Europe continues to bear the brunt of the epidemic, however, accounting for over 45,000 of the worldwide deaths, and Britain reported a new daily high in fatalities.
There are now more than 1.17 million confirmed coronavirus cases around the world and there have been 63,437 deaths since the virus emerged in China late last year.