TOEFL Integrated Writing

📖 Reading Passage

The introduction of non-native species into new environments is often viewed solely as a threat to biodiversity, but recent research suggests that, under certain conditions, such introductions can actually provide ecological benefits. Three key arguments support this controversial perspective. First, non-native species can fill vacant ecological niches. In habitats degraded by human activity, native species may have vanished, leaving roles unfilled. For example, in the Hawaiian Islands, the introduced Japanese white-eye bird has taken over the pollination of native flowers that lost their original pollinators, thereby sustaining plant reproduction. Second, non-native species can enhance ecosystem resilience by increasing functional diversity. A study in New Zealand showed that introduced trout, by preying on invasive invertebrates, indirectly protected native aquatic plants, leading to a more balanced food web. Third, non-native species may serve as a genetic reservoir. When native populations face extinction due to inbreeding depression, introduced relatives can interbreed with them, introducing beneficial genetic variation. The case of the Florida panther, which was saved from extinction by crossbreeding with a introduced Texas cougar subspecies, demonstrates this potential. Thus, rather than being universally harmful, non-native species can play constructive roles in ecosystems.

🎧 Listening Lecture

The reading presents an optimistic view of non-native species, but this perspective is deeply flawed and ignores critical ecological evidence. First, the claim that non-native species fill vacant niches is misleading. Vacant niches rarely exist in stable ecosystems, and when a non-native species appears, it often outcompetes remaining native species for resources. In Hawaii, the Japanese white-eye, rather than merely pollinating, has displaced native pollinators and spread avian diseases, causing further declines in native bird populations. Second, the argument about increased resilience is contradicted by empirical data. In the New Zealand example, introduced trout did reduce some invasive invertebrates, but they also preyed on native fish and amphibians, leading to a net loss of biodiversity. The aquatic plant recovery was temporary and masked severe disruptions to the native food web. Third, the genetic reservoir idea is oversimplified. Interbreeding between non-native and native species often results in hybrid vigor that is maladaptive for the native species. In the Florida panther case, while crossbreeding increased population numbers, it also introduced genes that caused health problems, such as heart defects, and reduced the panther's ability to hunt its natural prey. Ultimately, the negative impacts of non-native species far outweigh any minor, context-dependent benefits, and conservation efforts should focus on preventing introductions rather than rationalizing them.