Rats' drastic effects on islands

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Rats have a reputation for avoiding water. But that doesn't prevent them from profoundly altering marine ecosystems.

Norway rats on the Aleutian Islands have drastically changed the type of organisms living along the shores between the high and low tide marks. They've done so by decimating the number of shorebirds that feed there, according to two scientists at the University of California at Santa Cruz.

The duo conducted field studies between 2002 and 2005 on 23 islands spread throughout the Alaskan archipelago. Eight islands had large rat populations, thanks to shipwrecks as early as the 1700s; 15 islands were virtually ratless. The scientists found that on the rat-infested islands, the rats had raided the birds' nests, eating the eggs and chicks. Without birds to control their numbers, snails and limpets proliferated and munched away at the seaweed dominating the shore between high and low tide marks. Mussels and sea stars replaced the seaweed on the rocky shoreline. On the rat-free islands, where birds flourished and dined on invertebrates, the intertidal zone remained dominated by seaweed.

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The study highlights how invasive species can have landscape-wide effects beyond the immediate impact they have on the species they wipe out. The results appear in this week's issue of the Proceedings of the National Academy of Sciences.

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