The Patriots have made substantial investments in their linebacking corps over recent seasons, as Dont'a Hightower was a first round pick in 2012, Jamie Collins the team's top draft choice in 2013 and Jerod Mayo the recipient of a five-year extension near the close of the 2011 regular season.
The top end of the depth chart at the position seems to be mostly in place (the starting trio from last year returns in 2013), but there's a number of players in the mix for depth purposes, including Jeff Tarpinian, the subject of this morning's Bubble Watch post by Mike Rodak.
Tarpinian enters his third year in the program in 2013 after initially making the Patriots roster as an undrafted linebacker in 2011 out of Iowa. An injury cut that season short, while he became a practice squad player in 2012.
As was laid out by Rodak, other players who offer core special teams value are competition for Tarpinian, but one other wrinkle of note related to the 25-year old is that, should the Patriots want to have him on the practice squad, the active roster will need to be at 53 players on every game day. That's because 2013 would be Tarpinian's third year on the practice squad, and teams are required to have a full boat on the active roster if they want to keep a third year practice squadder (this same stipulation applied to James Develin last year).
There were weeks last year that the Patriots kept just 52 players on the active roster, and while not a major storyline, it's a part of the roster construction that the team keeps in mind as the season progresses. It doesn't decide the fate for a player like Tarpinian, but it's one of the many factors that is considered when evaluating his roster status.