新托福阅读材料：8WildWaystoCombatInvasiveSpecies（2）
外来入侵物种对本地区的生态系统会造成许多不良影响，科学家们用自己的聪明才智研究出了许多对抗这些“外来侵略者”的有趣方法。接下来我们就一起来看看吧! Sniffing for Snakes on GuamThis tenacious terrier isn't searching for illicit drugs or bombs, he's sniffing for stowaway snakes. The tiny island of Guam is infested with them. In the past 50 years the invasive snakes have wreaked havoc on the island's native birds and lizards. Now the U.S. Department of Agriculture (USDA) uses dogs to prevent them from sneaking off the island and damaging other islands.
The brown tree snake—a native of Australia, Papua New Guinea and the Solomon Islands—arrived in Guam in the 1940s or 50s, most likely hidden in a load of cargo. Soon it began breeding in the wild. Guam was a brown tree snake's paradise, free of predators and full of defenseless prey. "They populated the whole island in relatively short order," says Daniel Vice, assistant state director of USDA Wildlife Services in Hawaii, Guam and the Pacific Islands.
At the peak of the population explosion, the island may have had more than 30 snakes per acre of forest. Since the snake's arrival, nine native bird species have disappeared from the wild. The two remaining species are "perilously close to extinction," Vice says. The snakes also bite locals and climb on power lines, causing frequent small-scale blackouts.
Naturally, other islands would like to avoid the Guam's fate. In 1993 the USDA set up the Brown Tree Snake Control Plan to keep the secretive snakes from sneaking off Guam. Officials set up traps and laid out toxic bait. They also began inspecting outgoing cargo. But brown tree snakes aren't easy to spot. A meter-long snake can fit inside a soda can with plenty of room to spare, Vice says. The inspectors needed something better than their own eyes to search for snakes. That's when they came up with the idea of snake-sniffing dogs.
Today, the USDA relies on a team of 16 Parson (Jack) Russell terriers. The dogs patrol Guam's ports and cargo warehouses "24 hours a day, seven days a week," Vice says. But because the other snake control measures work so well, they don't find many snakes—maybe half a dozen each year. Still, Vice points out that those are "high-risk snakes"—the ones ready to be shipped off the island. These dogged canines are the last line of defense.
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