קראו את הקטע וענו על השאלות: הזאבים של ילוסטון

In 1995, scientists returned a small number of wolves to Yellowstone National Park in the United States, seventy years after the last ones had been killed. What followed surprised almost everyone. The wolves hunted deer, which had grown too numerous and had eaten young trees down to the ground. As the deer became more careful and avoided open valleys, the trees finally had a chance to grow. Birds returned to the taller branches, and beavers, which feed on wood, built dams in the rivers. Those dams created ponds for fish and insects. Even the rivers themselves changed shape, because stronger plant roots held the banks together and reduced erosion. This chain of effects, in which one species influences an entire landscape, is often called a trophic cascade. It reminds us that removing a single animal can quietly reshape a whole system, and that returning it can heal one too.

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