A Ranger's Companion (PH p.93) enjoys the following bonuses relative to a typical member of its species:
Add your proficiency bonus to the beast's AC, attack rolls, and damage rolls, as well as to any saving throws and skills it is proficient in.
In the case of skills and saves, does the Ranger's proficiency bonus replace the normal +2 proficiency bonus a CR ¼ beast is entitled to (MM p.8)? Or do the two proficiency bonuses stack instead?
Does the Ranger have to be present to grant these bonuses?