It turns out that the nutrient-poor volcanic soils of the Aleutian archipelago can only support dense grasslands if they receive regular doses of fertilizer in the form of bird droppings. On islands without foxes, seabirds transfer nutrients from the ocean to the land by feeding on marine fish and invertebrates and spreading nutrient-rich guano around the islands. Add foxes, and the indirect effects on the whole ecosystem are as dramatic as the direct effects on the seabirds.
"Introduced species are a global phenomenon, and we tend to focus on the direct effects, such as the reduction or extinction of species that are consumed by an introduced predator. This study shows how the effects of introduced species can spread throughout an ecosystem in unpredictable ways," said Donald Croll, an assistant professor of ecology and evolutionary biology at the University of California, Santa Cruz, and first author of the Science paper.
Efforts by the U.S. Fish and Wildlife Service to remove introduced foxes from the Aleutian islands have been largely successful. Seabirds are beginning to make a comeback on islands previously colonized by foxes, and in some places the vegetation has begun to look lusher. But it is likely to take decades for the ecosystems to fully recover from the effects of the foxes, said James Estes, adjunct professor of ecology and evolutionary biology at UCSC and a coauthor of the paper.
"Most seabirds only have a single offspring each year, so their cap
Source:University of California - Santa Cruz