SANTA CRUZ, CA--Feral pigs have created ecological havoc in many parts of California, uprooting native plants and turning meadows into mudholes. But nowhere have their effects been as dramatic as on the Channel Islands, where they have caused a complete restructuring of the food web, threatening the native island fox with extinction. A team of biologists has now documented the remarkable extent to which the introduced pigs have disrupted the island ecosystem. They are reporting their findings in the scientific journal Proceedings of the National Academy of Sciences (the article will be published online on December 18 and will appear in print in the January 8 issue of the journal).
The story involves not only exotic pigs and native foxes, but also golden eagles that have recently colonized the islands and a native spotted skunk. Golden eagles were initially drawn to the islands by the abundance of tasty piglets on Santa Cruz, the largest of the Channel Islands. But they began preying on the island fox as well, causing the fox population to plummet not only on Santa Cruz but also on the nearby islands of Santa Rosa and San Miguel. The cat-sized island fox, once the dominant predator in the ecosystem, is rapidly disappearing. Meanwhile, skunk populations are booming due to reduced competition from foxes.
"The presence of exotic pigs has totally restructured the food web on Santa Cruz Island," said Josh Donlan, science director for the nonprofit Island Conservation and Ecology Group based at the University of California, Santa Cruz, and a coauthor of the paper.
At first glance, it might appear that feral pigs are outcompeting the foxes, but the two species are not direct competitors, said lead author Gary Roemer, now at New Mexico State University.
"This phenomenon is called apparent competition--the two prey species share a predator that has an asymmetric impact, causing one species to decline," Roemer said. "This is the first case tha
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Contact: Tim Stephens
stephens@cats.ucsc.edu
831-459-4352
University of California - Santa Cruz
17-Dec-2001
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