The introduction of non-native species into new environments is often viewed as a threat to biodiversity, but in some cases, it can actually be beneficial. One such example is the deliberate introduction of the Asian clam (Corbicula fluminea) into North American freshwater ecosystems. This practice should be encouraged for three reasons. First, Asian clams are highly effective filter feeders, capable of clarifying water by removing algae and suspended particles. This improves water quality, which benefits other aquatic organisms that require clear water for photosynthesis and foraging. Second, these clams provide a new and abundant food source for native predators, such as certain fish and birds, which may help boost their populations. Third, Asian clams are resilient and adaptable, thriving in a wide range of temperatures and water conditions, which means they can establish stable populations with minimal human intervention. This resilience ensures that their ecological benefits are long-lasting and cost-effective, making them a practical tool for ecosystem management.
🎧 听力讲座
The reading suggests that introducing Asian clams is beneficial, but this view is overly optimistic and ignores significant negative consequences. First, while Asian clams do filter water, they also compete with native filter feeders, such as unionid mussels, which are already endangered. By removing algae and particles, Asian clams starve native mussels, leading to their decline and reducing overall biodiversity. Second, although Asian clams may be a food source for some predators, they are not nutritionally equivalent to native prey. Studies show that clams have a high shell-to-meat ratio, meaning predators must consume more to gain the same energy, which can lead to decreased predator fitness. Moreover, their rapid reproduction can outpace predation, causing their populations to explode and dominate the ecosystem, crowding out native species. Third, their resilience is actually a double-edged sword. Because they can tolerate a wide range of conditions, they spread rapidly and are nearly impossible to eradicate once established. This leads to biofouling of water intake pipes and other infrastructure, causing economic damage. Additionally, their filtering activity alters nutrient cycles, which can lead to oxygen depletion in bottom waters, harming fish. Therefore, the supposed benefits are outweighed by severe ecological and economic costs.
📝 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.