(Alopex lagopus) was introduced into the Aleutian Islands as a fur source following the collapse of the maritime fur trade at the turn of the 20th century. In a report in the current issue of Science, researchers describe the effect the foxes have had on the landscape. Comparing islands with foxes to those without, the scientists determined that the creatures were ultimately responsible for transforming their surroundings from grassland to tundra. By preying on the native seabirds, it seems, the foxes significantly reduced the amount of guano available to fertilize the resident flora, resulting in less productive plant communities dominated by low-lying shrubs.