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For thousands of years, green and gold grasses covered North America from Canada to Mexico. The prairie and desert grasslands were home to a variety of animals, from small prairie dogs to huge bison. But in the nineteenth century, ranching and farming took hold in the grasslands, and over time many of the animals and plants vanished.

Then, in the late 1980s, scientists discovered a region in Mexico where green and gold grasses still waved and prairie dogs still barked. The scientists understood the importance of this grassland ecosystem and the prairie dogs' key role in it. Could...