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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 a keystone species—the beaver. Now, beavers are often seen as pests by landowners, but ecologically they are incredibly important. When beavers build dams, they create wetlands, which are among the most productive ecosystems on Earth. These wetlands filter water, reduce erosion, and provide habitat for a wide variety of species, from fish to amphibians to birds. The dams also slow down water flow, which helps recharge groundwater and can even mitigate the effects of drought. Interestingly, the ponds created by beavers also trap carbon, so they play a role in climate regulation. However, beaver populations have declined significantly due to hunting and habitat loss. Some conservation efforts now involve reintroducing beavers to areas, and the results have been surprisingly positive. For example, in some parts of the United Kingdom, beaver reintroduction has led to improved water quality and increased biodiversity. So, while beavers might cause localized flooding, their overall benefits to the environment are substantial.