The introduction of non-native species into new environments is often viewed negatively, but in many cases it can actually be beneficial. Three key arguments support this claim. First, non-native species can enhance biodiversity by filling ecological niches that native species have not occupied. For example, the introduction of the saltcedar tree to the southwestern United States provided new habitats for certain bird species, increasing local avian diversity. Second, non-native species can offer economic benefits. The cultivation of the Pacific oyster in the waters of the Pacific Northwest, though originally from Japan, has become a multimillion-dollar industry, providing jobs and a sustainable food source without displacing native oyster populations. Third, non-native species can contribute to ecosystem resilience. In the Great Lakes, the introduction of the zebra mussel, despite initial concerns, has improved water clarity by filtering large amounts of algae, which has benefited native aquatic plants and the fish that depend on them. These examples illustrate that non-native species, when managed properly, can have positive ecological and economic impacts.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
The reading argues that non-native species can be beneficial, but this view overlooks critical long-term consequences. First, while saltcedar may provide habitats for some birds, it drastically reduces biodiversity overall. Saltcedar consumes excessive water, lowering water tables and outcompeting native willows and cottonwoods, which support a wider range of insects and birds. The net effect is a loss of native species and a simplification of the ecosystem. Second, the economic benefits of non-native species like the Pacific oyster are often overstated. In reality, oyster farming has introduced diseases and parasites that have devastated native oyster populations, leading to costly management efforts. When such externalities are considered, the economic gains are offset by environmental damages and restoration expenses. Third, the zebra mussel's water-clearing effect is not a benefit but a disruption. By filtering out phytoplankton, zebra mussels remove the base of the aquatic food web, causing declines in native fish populations. They also clog infrastructure, costing billions in maintenance. Thus, the supposed benefits are short-term and outweighed by severe ecological and economic harms.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
