London, July 18 : Fossil remains have proved that certain plants found on the Galapagos Islands, which were thought to be invasive species brought there by humans, have actually grown there for at least a millennium.
According to a report in Nature News, this means that the presence of the invasive species predate humans' arrival.
Sorting the native plant life from the trespassers is essential to conservation efforts.
Since the Bishop of Panama landed there in 1535, people have, intentionally or accidentally, brought goats, blackberries, fire ants and a host of other species to the archipelago, altering an ecosystem valuable to both evolutionary biologists and nature lovers.
The islands' 825 introduced species outnumber the 552 plants that are native to the islands. There are also 62 plant species classified as "doubtful natives", and scientists aren't sure if they were present before humans got there or not.
"Whenever you're dealing with island studies, one of the most important factors is where things came from, how they got there and when," said Conley McMullen, a botanist at James Madison University in Harrisonburg, Virginia, who has worked in the Galapagos.
By examining fossil remains in sediment samples from Santa Cruz island, Emily Coffey, a graduate student at the University of Oxford, UK, has now confirmed that at least four of those questionable natives, including a species of hibiscus, existed on the island 1,000 years ago.
To collect their samples, Coffey and her collaborators trekked to the misty highlands of Santa Cruz. They drilled into the bogs, where sediment has settled for millennia.
Coffey is collaborating with researchers examining fossil pollen, and more species are likely to be reclassified as natives in the future.
A fossil Argeratum conyzoides seed confirms that the plant was in the Galapagos Islands before humans arrived.
Scientists have often assessed the origins of a particular plant species by studying its distribution: those spread across an island are likely to be native, while those clustered around human habitation are presumed invasive.
"But there's only one way to be sure, and that's to look in the paleoecological record," said Keith Bennett, a paleoecologist at Queen's University Belfast in Northern Ireland.