I would be more inclined to think if there is a decline in deer population, it would be because of the wolves. Mountain lions, are generally loners, and make a large kill, maybe once a week or less, and making smaller kills of opportunity, in between when attempts at larger game fails. They will feed off of a large carcass for days. Whereas Wolves will make multiple kills a week, due to the number in the pack. Plus if the game is plentiful, they will make kills just to kill, then when the number of big game goes down, they will start consuming the kills. Wolves do not always kill for survival.
Montana, Wyoming, and Idaho, can attest to that!
Wayne