Roster turnover is a fact of life in college football. Each autumn brings new faces to replace departed heroes. The newcomers’ untapped potential sparks the imagination and generates fresh hope, and that’s part of the fun.

But it’s not always easy, and sometimes it’s practically impossible.

Here’s our look at the bygone stars who left a mark on their programs and will not be easily replaced in 2015.

Alabama — Amari Cooper: The Crimson Tide recruits well across the board, but talents like Cooper don’t come along every couple of years. Cooper set the SEC single-season record for receptions in 2014 and was near the top of the record book in receiving yards and touchdowns. And while Cooper is the most notable, Alabama lost all three of its top options at receiver. Sophomore ArDarius Stewart could be emerge as the leader of this year’s group, and true freshman Calvin Ridley has the look of a star in the making.

Arkansas — Martrell Spaight: Among a trio of key losses in the Hogs’ front seven, Spaight could prove tougher to replace than defensive end Trey Flowers or defensive tackle Darius Philon. Even with those departures, Arkansas appears to have a deep group returning on the defensive line. Aside from Brooks Ellis, however, there are question marks at linebacker, where Spaight led the conference in tackles last season.

Auburn — Sammie Coates: Duke Williams could very well be the best receiver in the SEC in 2015, but with the Tigers expected to air it out more in 2015, it would be nice to have a target of Coates’ caliber on the opposite side. Before turning pro, Coates was the receiver most responsible for taking the tops off of opposing defenses, leading the 2014 team in receiving yards and finishing with nearly 22 yards per reception. Ricardo Louis and Melvin Ray have each shown play-making ability in their careers, but there is no immediate answer for who will replace Coates’ production in 2015.

Florida — Max Garcia: The Gators are in total rebuild mode up front, and while they’ve got some very attractive pieces to work with, depth could be an ongoing concern. Garcia’s leadership, versatility and talent will be especially missed. He started 24 games in his two years with the Gators, including all 12 at center in 2014. Sophomore Cameron Dillard and freshman Tyler Jordan and vying for the starting spot this year.

Georgia — Hutson Mason: Mason may not have the NFL talent of Georgia’s other losses from last season, but his absence leaves the biggest question mark heading into the 2015 season. As of Thursday, the Bulldogs hadn’t yet decided on a starting quarterback and were planning to play both Greyson Lambert and Brice Ramsey in the season opener against Louisiana-Monroe. And whatever limitations Mason may have had, his efficiency (67.9 completion percentage, 21 TDs, 4 INTs) can’t be faulted. If the Bulldogs get similar play at the position this fall, a trip to Atlanta could await in December.

Kentucky — Bud Dupree: The Wildcats struggled defensively last year and they’ll be looking for improvement in 2015 without the services of their most productive defender. Dupree finished 2014 with 7.5 sacks and 12.5 tackles for losses to lead the team in both categories from his rush end position. Kentucky will be looking to senior Jabari Johnson to provide a pass rush from the hybrid end/linebacker spot.

LSU — La’el Collins: LSU should be fine at tackle; Jerald Hawkins is moving over to the left side, Vadal Alexander is sliding out from his guard position, and both have been rock solid since the spring. Other than the defensive ends, both of whom disappointed in 2014, the Tigers didn’t lose many players off last year’s team that they don’t have ready-made replacements for, and Collins’ All-SEC talent alone means that some drop-off at line’s most important position is almost unavoidable.

Mississippi State — Dillon Day: The Bulldogs will be missing three key pieces of last year’s offensive line. We’ve singled out Day, not only for his consistently strong play, but also for the fact that the Bulldogs don’t have a player on the roster who has ever played a college game at center. The duties in 2015 will fall to Jamaal Clayborn, a former guard who began the transition during last year’s bowl practices.

Mizzou — Harold Brantley: Shane Ray might’ve been Missouri’s best player in 2014, but the unexpected loss of Brantley for the 2015 season dealt a painful blow to the foundation of the Tigers defense. Expected to be the leader of a revamped defensive line, Brantley was involved in a serious car crash in June and sustained a broken leg, knee ligament damage, broken ribs and a shoulder injury. There’s little experience remaining in this year’s front four, but Josh Augusta and Rickey Hatley are the leading candidates at the interior positions, and freshman Terry Beckner Jr. could be a difference maker early in his career.

Ole Miss — Senquez Golson: The Rebels will surely miss Cody Prewitt playing the defense’s enforcer role, but it’s hard to argue with the outright productivity of Golson’s 2014 season. The undersized corner recorded 10 of his 16 career interceptions last fall and recorded eight pass breakups en route to a consensus All-American status. A pair of junior college transfers, Tee Shephard and Tony Bridges, are being looked at as possible replacements.

South Carolina — Dylan Thompson: His lone season as the Gamecocks’ starter under center didn’t go as well as hoped, so it’s easy to forget that Thompson actually led the SEC in passing yards last season with 3,574 yards. In his place steps Connor Mitch, who attempted only six passes last year. He’ll be taking over an offense that has averaged at least 30 points per game six straight years and has numerous playmakers returning at the skill positions.

Tennessee — A.J. Johnson: Johnson leaves Tennessee second on the school’s all-time tackle list after finishing with 101 last season. His senior season was cut short by troubling off-the-field allegations, and the Vols struggled at times without their four-year starter at middle linebacker down the stretch. Vying to fill the spot this year are sophomore Colton Jumper and true freshman Darrin Kirkland.

Texas A&M — DeShazor Everett: Though more has been made of the Aggies’ difficulties against the run last year, they had their problems against the pass as well. New defensive coordinator John Chavis should help out on both fronts, but his job would be made easier without the loss of Everett, a three-year starter at cornerback. The Aggies are looking for Victor Davis or Brandon Williams to emerge at the spot opposite established senior De’Vante Harris.

Vanderbilt — Vince Taylor: The good news after a 3-9 campaign in 2014 is the Commodores return just about everybody. One notable exception is Taylor, leaving Vanderbilt without a proven nose tackle to anchor Derek Mason’s 3-4 defense. Nifae Lealao is perhaps best-suited to handle the position, though the Commodores will likely cycle multiple players through their defensive line rotation. The team also has lost projected offensive starters Patton Robinette, C.J. Duncan and Andrew Jelks since the end of spring practice.