Published online 17 July 2008 | Nature | doi:10.1038/news.2008.959

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Galapagos invaders go native

Plant fossils prove that species' presence predated humans' arrival

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.

Pernettya bogThe lush Pernettya bog is one of the Galapagos sample sites.E. Coffey

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" — 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," says 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. Coffey is collaborating with researchers examining fossil pollen, and more species are likely to be reclassified as natives in the future.

Seed fossilA fossil Ageratum conyzoides seed confirms that the plant was in the Galapagos Islands before humans arrived.E. Coffey

"I'm trying to truly understand what humans have done," she told Nature. Coffey presents her research today at the Society for Conservation Biology annual meeting in Chattanooga, Tennessee.

Unwelcome guests

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," says Keith Bennett, a paleoecologist at Queen's University Belfast in Northern Ireland, who calls Coffey's work "very exciting".

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. Other islands lacked the undisturbed environment the researchers sought. On Pinta, "very sadly, there had been a peat bog there but the goats had destroyed it," Coffey says.

CoringScientists use a drill to collect a sediment sample.E. Coffey

The numbers of invasive species identified in the Galapagos has skyrocketed in the past couple of decades, as ecotourists flock to the islands and others migrate there to work. In part, the spike is due to better identification of non-native plants. Johannah Barry, president of the Galapagos Conservancy in Fairfax, Virginia, notes that traffic to the archipelago has increased dramatically. In 1991, there were three flights a week to the islands; now there are five flights daily. "There are more opportunities for something to hitch a ride," she says.

Park rangers and the Charles Darwin Foundation in the Galapagos are working to restore the islands to a pristine condition. They have already succeeded in cutting back on the invasive quinine tree, using rings around the trunk to strangle the trees. Coffey’s research will help rangers to decide which plants to weed out and which to leave alone.

"We haven’t hit a tipping point yet," Coffey says. "We can address some of these problems, how we’re impacting the islands, and really make a difference." 

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