This should cover just about everything:

http://www.nps.gov/yose/index.htm

Yosemite Valley is extremely crowded during the summer, Touloume Meadows a litle less, but still a lot of people. Make reservations as soon as you can.

Lots of wildlife, some very dangerous. Mountain lions, bears, but the most feared is the Yosemite Wall Rat. If you see this feral creature be sure to keep your distance and lock up all food and valuables.

ExcitableBoy wrote:Lots of wildlife, some very dangerous. Mountain lions, bears, but the most feared is the Yosemite Wall Rat. If you see this feral creature be sure to keep your distance and lock up all food and valuables.

If they are far away enough that binoculars are needed to spot them though, you are safe.