托福听力

🎧 听力原文

Listen to part of a lecture in an environmental science class. The professor is discussing the role of beavers in ecosystems. Professor: So, we often think of beavers as simply tree-eating rodents, but their impact on the environment is far more complex and beneficial. Beavers are what we call 'ecosystem engineers' because they physically alter the landscape, creating wetlands that didn't exist before. When they build dams, they slow down the flow of streams, causing water to spread over the surrounding floodplain. This creates a mosaic of ponds, marshes, and wet meadows. These wetlands serve as critical habitats for a wide variety of species, from amphibians and fish to birds and insects. Moreover, the stagnant water in these beaver ponds traps sediments and pollutants, improving water quality downstream. The dams also help to recharge groundwater aquifers. Interestingly, recent studies have shown that beaver activity can even mitigate the effects of droughts and floods by storing water during wet periods and releasing it slowly during dry ones. So, far from being a nuisance, beavers play a vital role in maintaining biodiversity and ecosystem resilience.