The introduction of the cane toad (Bufo marinus) to Australia in 1935 is widely regarded as an ecological disaster. Originally imported to control agricultural pests, the toad has since become an invasive species with devastating effects. Three main arguments are often cited to explain why the cane toad is so harmful. First, the cane toad is highly toxic. Its skin and parotoid glands secrete a potent toxin called bufotoxin, which is lethal to many native predators such as snakes, lizards, and quolls. When these animals attempt to eat the toad, they die quickly, leading to population declines and disruption of the food chain. Second, the cane toad has an exceptionally high reproductive rate. A single female can lay up to 30,000 eggs per year, and the tadpoles develop rapidly in a variety of water bodies. This allows the toad population to explode, outcompeting native amphibians for food and breeding sites. Third, the cane toad occupies a broad ecological niche. It can thrive in diverse habitats, from rainforests to arid regions, and it feeds on a wide range of invertebrates and even small vertebrates. This adaptability enables it to spread across the continent, causing widespread ecological imbalance.
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The reading presents the cane toad as an unmitigated threat, but this view is oversimplified and ignores important counterpoints. First, while the toxin is indeed dangerous, native species are not entirely defenseless. Some Australian predators, such as the red-bellied black snake, have developed behavioral adaptations—they avoid the toad’s toxic glands or have evolved partial resistance. Moreover, recent studies show that populations of some native predators are recovering as they learn to avoid the toad, suggesting that the impact may be temporary, not permanent. Second, the high reproductive rate is not unique to cane toads. Many native Australian frogs also produce large numbers of eggs, and their tadpoles often share similar habitats. In fact, cane toad tadpoles are vulnerable to predation by native dragonfly larvae and fish, which limits their survival. Thus, the toad does not necessarily outcompete native species; it merely adds to the competition. Third, the broad ecological niche is not a disadvantage but rather a sign of adaptability. However, this adaptability has limits. Cane toads require moist environments for breeding, and they cannot survive in extremely dry or cold regions. Consequently, their distribution is naturally restricted to certain areas, and they do not occupy all of Australia. In sum, the cane toad problem is significant but not as catastrophic as the reading suggests, and native ecosystems are showing resilience.
📝 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.
