ECOLOGY: The Eagle Has Landed

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Science  08 Feb 2002:
Vol. 295, Issue 5557, pp. 931b
DOI: 10.1126/science.295.5557.931b

Introduction of alien species, especially to islands, often has dramatic effects on native ecosystems and their flora and fauna.

Roemer et al. report a case of wholesale restructuring of the predator community in the California Channel Islands, after the introduction of an exotic prey species—the pig. The ensuing abundance of feral piglets enabled a top predator species, the golden eagle, to colonize from the mainland. The eagles also preyed on the islands' native mammalian predators—foxes and skunks—and thereby altered the competitive dynamics of these two species. The island skunks, being mainly nocturnal, were less vulnerable than foxes to eagles. The fox populations declined rapidly, allowing the skunk population to increase as its dominant competitor became increasingly scarce. This case illustrates how the introduction of a prey species can indirectly cause the decline of a predator, probably leading to cascading effects down the rest of the food chain. — AMS

Proc. Natl. Acad. Sci. U.S.A.99, 791 (2002).

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