We need more cougars

(Thanks to Elizabeth for calling my attention to this one.)

In Yosemite, the paper says, the direct cause of oak mortality is the high density of mule deer, which have been munching the oaks' basal sprouts and seedlings for nearly a century. Intriguingly, the mule deer's abundance stems not from a lack of predators--as with elk in Yellowstone National Park (Science, 27 July 2007, p. 438)--but from shy ones: elusive cougars (Puma concolor). The mountain lions keep the deer in check elsewhere in the park but avoid areas like the valley, where people congregate.

- Science magazine (no link provided)