So Rep. Chip Cravaack (R), who holds Minnesota's 8th district, can thank his lucky stars he still has a seat in which to run in two years (Actually, rumors out of Minnesota put Rep. Michele Bachmann's 6th District most at risk if the state had lost a seat). And, because their seats were narrowly eliminated, Reps. Blaine Luetkemeyer (R-Mo. 09), Louise Slaughter (D-N.Y. 28), Albio Sires (D-N.J. 13), Charles Boustany (R-La. 07) and Tim Ryan (D-Ohio 17) all need to begin looking for new seats.
The obvious caveat: Decennial redistricting leads to a lot of new lines, meaning many members will have to run in new districts. The members mentioned above are just the ones who already know they can't seek another term in their old seats.
Wonder why the additional population needed to gain an extra seat isn't ranked from lowest to highest? Check out the math behind the Method of Equal Proportions, adopted by Congress in 1941 as the means by which reapportionment takes place, here. Or, for the less mathematically inclined (this author very much included), watch the Census Bureaus' handy explanatory video, below.