托福听力

🎧 听力原文

Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a fascinating example of ecosystem engineering—beavers. Beavers are often called ecosystem engineers because they dramatically alter their environment. When they build dams across streams, they create ponds that flood the surrounding area. This may seem destructive at first, but it actually creates a wetland habitat that supports a huge diversity of species. For instance, the still water in the pond attracts amphibians, insects, and waterfowl. The dead trees in the flooded area become nesting sites for birds and provide food for insects. Over time, the pond fills with sediment and becomes a meadow, which then supports different species like grasses and small mammals. Interestingly, this process can repeat as beavers move upstream and build new dams, creating a mosaic of habitats at different stages. So, while beavers are just trying to build a safe home, they unintentionally benefit entire ecosystems. This shows how one species can have a profound impact on biodiversity.