HOUSTON -- (Sept. 13, 2012) -- In one of the first studies to examine how the loss of forest birds is effecting Guam's island ecosystem, biologists from Rice University, the University of Washington and the University of Guam found that the Pacific island's jungles have as many as 40 times more spiders than are 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," said Haldre Rogers, a Huxley Fellow in Ecology and Evolutionary Biology at Rice and the lead author of a new study this week in the open-access journal PLOS ONE.
The results are some of the first to examine the indirect impact of the brown treesnake on Guam's ecosystem. The snake, which was accidentally introduced to the island in the 1940s, 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, and the last two live only in small areas protected by intense snake-trapping.
Rogers and colleagues are investigating whether the loss of birds led to an increase in the spider population on Guam, since many birds consume spiders, compete with spiders for insect prey and utilize spider webs in their nests. Small-scale experiments in other ecosystems have consistently shown a link between the presence of birds and the abundance of spiders, but the new study is the first examine the impact of bird loss on the scale of an entire forest.
Counting spider webs on Guam and on nearby islands in the Marianas Islands chain was the first step. Rogers said the difference between the number of spiders she and her colleagues counted on Guam and three nearby islands that still have birds "was far more dramatic than what any small-scale experiments had previously found." She said the findings underscore the importance of using both observed counts and controlled experiments
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