History and snakes: Guam





One of the most infamous examples of what can happen when a nonnative species is introduced into a new environment involves the brown tree snake -- a voracious, semi-venomous species that in less than 50 years all but destroyed bird life on the northern Pacific island of Guam. Introduced inadvertently from the South Pacific just after World War II, apparently on a cargo ship, the snake has killed off 10 bird species on the island and is in the process of wiping out the remaining two.

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Snake's Impact on Guam Appears to Extend to Flora
Transcript: Science: Impact of Tree Snakes in Guam
Knocking a Forest Off Balance
The virtual extermination of Guam's birds has been bemoaned for decades, but new research suggests that the damage to the ecology of the narrow, 30-mile-long island did not stop there.

The hundreds of thousands of snakes, researchers say, are now changing the way Guam's forest grows and will most likely cause substantial thinning and clumping of trees in the years ahead. In addition, the snakes appear to be indirectly responsible for an explosion in the spider population.

Guam, which is 3,800 miles west of Hawaii, did not have predatory snakes before the brown tree snakes arrived, and as a result the birds were not afraid of such creatures and not prepared for the onslaught. The snakes have few natural predators on the island and have at times climbed electric poles in their search for young birds, causing power outages.

"The brown tree snake has often been used as a textbook example for the negative impacts of invasive species, but after the loss of birds no one has looked at the snake's indirect effects," said Haldre Rogers, a University of Washington doctoral student in biology who presented her findings last week at the Ecological Society of America's annual meeting.

Rogers, who first went to Guam in 2002 as part of a U.S. Geological Survey "rapid response team" in a bid to keep the snakes from spreading, said she has studied tree growth on Guam and neighboring islands and has found "amazing" differences.

Without birds, which eat the seeds of certain trees and then spread them in their droppings, those trees are losing out to others that do not depend as much on bird middlemen. The seeds of the trees that relied on birds are now falling mostly near the trunks of the parent trees, where they are more likely to be spoiled by fungus and less likely to grow into healthy trees. The result, Rogers said, will either be the loss of some tree species or the clumping of those trees in isolated patches...



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