TOEFLリスニング

🎧 リスニング原文

Listen to part of a lecture in an environmental science class. The professor is discussing the role of beavers in ecosystems. Professor: Today, we're going to talk about beavers, and specifically, how they act as a keystone species. A keystone species is one that has a disproportionately large effect on its environment relative to its abundance. Beavers do this primarily through dam building. When they build a dam across a stream, they create a pond. This pond slows down the water, which allows sediment to settle. This improves water quality downstream. The pond also creates new habitats for fish, amphibians, and insects. Interestingly, the flooded area kills some trees, but these dead trees provide food and shelter for woodpeckers and other birds. Moreover, beaver ponds help recharge groundwater and can even reduce the risk of downstream flooding by storing water during heavy rains. However, beaver activity can also cause conflicts with humans, such as flooding roads or timberlands. So, while beavers are beneficial, their presence sometimes requires careful management.