In addition to Croll and Estes, the authors of the Science paper include UCSC graduate student Eric Danner, University of Montana plant ecologist John Maron, and USFWS biologist Vernon Byrd. The study grew out of conversations between Estes, who has been doing research in Alaskan coastal waters for decades, and Byrd, the supervisory biologist for the Alaska Maritime National Wildlife Refuge. While working to save the endangered Aleutian Canada goose, which the foxes were driving toward extinction, Byrd had noticed the differences between islands with and without foxes and speculated that nutrients might play a role.
"He had these interesting ideas about foxes and birds and nutrient chains, and I thought we should do some studies to see how robust the idea is," Estes said.
The team of researchers, accompanied by a small army of student assistants, conducted extensive surveys on the islands for several weeks each summer over three years. They surveyed dozens of islands from one end of the archipelago to the other. Estes said the differences were striking between fox-free islands and fox-infested islands (defined as those where self-sustaining populations of foxes persisted into the late 1990s).
"When you go to an island that had foxes, it's very easy to walk around because the plants don't grow much higher than your ankles. But on the other islands, it's hard work just to get through the vegetation. It was exhausting just trying to get around on those islands," he said.
The researchers found that the density of breeding seabirds on fox-free islands was two orders of magnitude higher than on fox-infested islands. The resulting difference in nutrient inputs was reflected in soil phosphorus levels that were more than three times higher on fox-free islands. The vegetatio
Source:University of California - Santa Cruz