After direct habitat destruction, nonnative species introduced by humans to new areas pose the largest threat to global biodiversity. This program looks at how scientists and conservationists are coping with a number of these critical situations, such as on Seychelles, where rats have caused 200 years of devastation; on Scotland’s Outer Hebrides, where hedgehogs were released to control garden slugs; and in New York City, where Asian longhorn beetles threaten not only Central Park but the forests of the entire east coast. Also examined are the political and economic difficulties of these species invasions when tensions arise between the interests of environmental protection and increasing trade. (25 minutes)