The introduction of non-native species into new environments is often viewed with alarm, but a growing number of ecologists argue that such introductions can be beneficial. This perspective, known as 'assisted migration' or 'ecological replacement,' suggests that humans should actively move species to help them survive climate change and restore degraded ecosystems. Three main arguments support this view.
First, non-native species can fill ecological niches left vacant by extinct or declining native species. For example, in the Hawaiian Islands, many native bird species have gone extinct, leaving gaps in seed dispersal and pollination. Introducing similar non-native birds could restore these essential ecosystem functions, thereby improving forest health.
Second, non-native species can enhance biodiversity at the regional scale. Critics often focus on local extinctions caused by invasives, but in many cases, introduced species increase the total number of species in a region. For instance, the introduction of non-native earthworms in North American forests has increased soil invertebrate diversity, which in turn supports a wider range of predators.
Third, non-native species are often more resilient to climate change than native species. Many native species are adapted to historical climate conditions and cannot cope with rapid warming. In contrast, non-native species from warmer regions may thrive under new conditions, providing ecosystem services such as carbon sequestration and erosion control that native species can no longer offer.
🎧 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 arguments in the reading are overly optimistic and ignore substantial ecological risks. While the idea of using non-native species to fill vacant niches sounds appealing, it fails to consider that introduced species often disrupt ecosystems in unforeseen ways. For example, the non-native birds proposed for Hawaii might compete with remaining native birds for food and nesting sites, potentially driving them to extinction. Moreover, these birds may introduce diseases to which native birds have no immunity, leading to further declines.
Second, the claim that non-native species increase regional biodiversity is misleading. While total species count may rise, this often comes at the cost of native species extinctions, leading to a homogenized biota where the same generalist species dominate worldwide. Earthworm introductions in North America, for instance, have reduced the diversity of native soil organisms and altered nutrient cycling, harming forest understory plants that depend on leaf litter.
Finally, the assertion that non-native species are more resilient under climate change is not a valid justification. Resilience does not equate to ecological value. Many non-native species are weedy and invasive, outcompeting native species and reducing overall ecosystem stability. Moreover, relying on non-natives to provide services like carbon sequestration overlooks the fact that native species may adapt over time if given conservation support. In summary, the reading's proposals are risky and short-sighted.
📝 ライティング指示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
