If someone turns down a university fellowship does it open up a spot for the waitlisted candidates in the same department? Recently I learned someone who received a university fellowship (with no TA duties) turned down the fellowship and position at a department I applied to for a doctorate. I was placed on a waitlist for admission to the program.
I'm wondering whether this creates a vacant spot (in the same department) or the funding goes somewhere entirely different, given it's funding provided by the university and not the department.
It's impossible to answer in the general sense. The two main constraints on PhD admissions are funding and mentorship capacity.
Someone who received a fellowship turning down the department might not free up any money, so it is possible the department does not have enough money to accept more people.
But that does free up a supervisory spot. So if the PI they intended to work with has the money, perhaps they would move to the waitlist.
Other factors can include the size of the previous cohorts. If they were large, then the department might take this opportunity to reduce the size of the department by not going to the waitlist.