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15 June 2007 (All day)
Plants lack legs, fins, or wings, but they still get around faster and easier than one might think. A study evaluating the origins of shrubs and herbs on a group of islands in the Arctic Circle finds that seeds arrived from hundreds of kilometers away to restore plant communities lost during the last ice age--all in a matter of a few thousand years. One of the first assessments of rapid, long-distance dispersal, the effort reinforces that plant communities can recover from devastating events. But the findings also mean that seemingly isolated flora are at risk of being replaced by southern species as the climate warms.
During ice ages, glaciers scour and cover large swaths of land, wiping out plant communities for millennia. Yet those communities have returned as ice has receded, and researchers have long debated just how far the new founding populations have traveled. Botanist Inger Greve Alsos, now at the University Centre in Svalbard, Norway, hoped a study of the Svalbard Archipelago would provide a definitive answer. Located between Greenland and Russia, Svalbard experienced a near-complete loss of its vegetation during the last ice age and was quite sparse even 10,000 years ago, but today it is home to a thriving plant community.
With the help of volunteers, Alsos, Christian Brochmann of the University of Oslo, and colleagues collected 4439 samples, representing nine plant species, from more than 500 Arctic populations in Greenland, Russia, Scandinavia, and Svalbard. By analyzing genetic markers called amplified fragment-length polymorphisms, the researchers could tell whether a Svalbard sample had, say, Russian ancestry, because of the many markers shared between that sample and a Russian one.
To the team's surprise, most of the Svalbard species hailed from multiple places--but predominantly from the farthest one, northwestern Russia, more than 1000 kilometers away. The diversity within each species indicated that six to 38 individuals--depending on the species--had to settle in Svalbard for that particular species to become established on the islands, Alsos's team reports today in Science.
The data indicate that plenty of seeds arrived--perhaps on driftwood on sea ice, or else blown there--but that not all these seeds were able to put down roots. Temperature seemed to be the determining factor. About 85% of the high Arctic plants found in Greenland, Russia, and Scandinavia had successfully settled in Svalbard, but only about 50% of species requiring slightly warmer temperatures had.
This foreign invasion is both good news and bad news for Arctic communities. On the one hand, notes Alsos, Arctic species will be able to disperse to new places better suited for them as the climate warms. On the other, current Arctic species are more prone to being displaced, says Richard Abbott, a plant evolutionary biologist at the University of St. Andrews in Fife, U.K. Given how relatively easy it is for seeds to get to Svalbard, "geographical isolation might not be a very effective barrier" to invasions by more southern species as the climate heats up, he says.