Sunday 16 September 2012

An abundance of spiders on Guam is the result of the loss of forest birds caused by an invasive snake that decimated the avian population, researchers say.

Biologists from Rice University, the University of Washington and the University of Guam found the loss of bird species has left the Pacific island's jungles with as many as 40 times more spiders than found on nearby islands like Saipan.

"You can't walk through the jungles on Guam without a stick in your hand to knock down the spiderwebs," Rice researcher Haldre Rogers said.

The biologists' study, published in the journal PLoS ONE, is the first to examine the impact of the brown treesnake on Guam's ecosystem.

Accidentally introduced to the island in the 1940s, the snake decimated the island's native bird species in one of the most infamous ecological disasters from an invasive species.

By the 1980s, 10 of 12 native bird species had been wiped out.

Since many birds consume spiders, compete with spiders for insect prey and utilize spider webs in their nests, their loss has led to a spider explosion on the island, researchers said.

"There isn't any other place in the world that has lost all of its insect-eating birds," Rogers said. "There's no other place you can look to see what happens when birds are removed over an entire landscape.

"Anytime you have a reduction in insectivorous birds, the system will probably respond with an increase in spiders. With insectivorous birds in decline in many places in the world, I suspect there has been a concurrent increase in spiders."


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