Historically, the herds were thinned by property owners allowing hunters to cull the older males each October. Now that so much land has been gobbled up by Preservationists for "open space" (closed to huners), the deer population is increasing exponentially, over grazing to the point of starvation and move onto roadways and into local neighborhoods. The mountain lion follow the deer and their numbers are increasing and will continue. When the eventual human fatality by the mountain lion predator, someone will ask, "how did this happen?"
Won't trapping the deer cause excessive stress on the animal? Tranq'd deer will wonder into oncoming traffic. Bring back the biodiversity which humans have participated for thousands of years prior to the DFG.