Agile, fast and fierce, cougars once hunted their prey throughout Yosemite National Park, but as human invasions and hunting began about 80 years ago, the predators steadily disappeared, and the entire ecology of the fabled valley was disrupted, researchers say they have discovered.

With fewer cougars to prey on them, Yosemite's mule deer multiplied and browsed on the tasty shoots of young black oak trees. The oaks disappeared, pines and firs replaced them, and even the wild evening primrose, known for its nutritious roots and its perfumed oil, grew rare among the altered plant growth in the valley's moist meadow soils.