The introduction of invasive species is often cited as a major threat to biodiversity, but the intentional introduction of non-native species can actually provide significant ecological and economic benefits. First, non-native species can fill vacant ecological niches. In many degraded ecosystems, native species have disappeared, leaving roles unfilled. For example, in Hawaii, the introduced myna bird helps disperse seeds of native plants, aiding forest regeneration where native bird dispersers are extinct. Second, non-native species can enhance economic productivity. Aquaculture relies heavily on introduced species like the Pacific oyster, which thrives in coastal waters worldwide and supports a multi-billion-dollar industry, providing jobs and affordable protein. Third, non-native species can increase genetic diversity and resilience. By hybridizing with native species, they can introduce traits that help populations withstand environmental stressors. For instance, introduced cordgrass in salt marshes has hybridized with native forms, producing offspring more tolerant to rising sea levels, thus stabilizing shorelines.
🎧 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 presents a rosy picture of non-native species, but this view is deeply flawed. First, the myna bird example ignores a critical fact: while it disperses some seeds, it also aggressively competes with native birds for nesting sites and food, and it spreads invasive plant seeds more effectively than native ones. Thus, it disrupts rather than restores ecosystems. Second, the economic benefits of aquaculture are overstated. The Pacific oyster, while profitable, has introduced diseases that decimate native oyster populations, and the need for constant disease control and containment imposes hidden costs that outweigh short-term profits. Moreover, fish farms often escape and interbreed with wild stocks, reducing their fitness. Third, the argument about genetic resilience is misleading. Hybridization with introduced cordgrass has produced aggressive hybrids that outcompete native plants, drastically reducing biodiversity in salt marshes. These hybrids also alter sediment dynamics, increasing erosion in some areas, and they are not proven to provide long-term stability under climate change. In fact, genetic mixing often leads to outbreeding depression, where hybrids have lower survival and reproduction. Therefore, the negative impacts of non-native species far outweigh any purported benefits.
📝 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.
