UNC? UCLA? Florida? What's happened to the hoops dynasties?

Presumptuous? Absolutely. Realistic? Most definitely. Recent history has shown that once a college football team gets to the top, it stays there for a good while. Go through a list of national champions from the 2000s -- Oklahoma, Ohio State, LSU, USC, Texas, Florida -- all turned themselves into top-10 fixtures.

College basketball's powerhouses don't enjoy the same stability.

Last season's NCAA champions, the North Carolina Tar Heels (12-7), currently find themselves mired in a three-game losing streak (their longest in seven years) and sit in 11th place in the ACC with a 1-3 league mark. On Tuesday, North Carolina visits N.C. State (13-7, 2-4), which knocked off Duke at home last week, and the Heels will likely be without injured big men Ed Davis and Tyler Zeller for the second straight game.

RoyWilliams' team began the season ranked sixth in the AP poll (and fourth in the coaches' poll), but as of Monday sat 73rd in the RPI rankings (according to CollegeRPI.com), and if the season ended today the Tar Heels would likely be headed to the the NIT.

"If you combine all my losses since I've been here, I'm about to pass that in one season," Tar Heels senior forward Deon Thompson said after last week's 82-69 home loss to Wake Forest. That's a bit of a stretch, though the Heels do already have as many losses as they did over the past two seasons.

What's wrong with the Tar Heels? There may be any number of technical answers (see my colleague Luke Winn's breakdown), but in the bigger picture, UNC's downfall seems somewhat inevitable.

Upon my return to the basketball beat for the first time in nearly two years, I'm struck by just how many of the sport's preeminent teams from the past few years have taken significant steps backward. Florida, which won back-to-back national championships in 2006 and '07, has failed to return to the NCAA tournament since and may find itself on the bubble again in March. (The 14-5 Gators sit 62nd in the RPI rankings.) UCLA, after reaching three straight Final Fours from 2006-'08, has plummeted to 9-10 this season.

Clearly, it's tougher than ever for hoops programs to remain consistently dominant, and it's easy to see why. The staggering extent of roster turnover from one year to the next requires coaches to bring in monster recruiting classes on a near-annual basis -- and heaven help you if even one or two of those new additions flames out.

Take the case of Florida. The core of BillyDonovan's title teams was the self-dubbed "0h-fours" -- classmates Joakim Noah, Al Horford, Corey Brewer and Taurean Green -- who stayed intact through their junior seasons but then left all at once, along with senior Lee Humphrey. Forced to essentially start from scratch, Donovan seemingly took the right steps to start reloading, landing McDonald's All-Americans Nick Calathes and Jai Lucas.

But Lucas lasted just one, relatively disappointing season, transferring to Texas (where he is now a reserve), and Calathes left last spring to play professionally in Greece. Florida's best "veteran" at the time, center Marreese Speights, entered the NBA draft as a sophomore. And several of Florida's biggest recruits the past few years (Allan Chaney, Eloy Vargas, Kenny Kadji) either transferred or failed to pan out. The Gators have yet to recover.

"It's been an unbelievable lesson for everyone involved: How fragile it all is," Donovan told The Sporting News last summer. "Two years ago, we win back-to-back national championships, and the past two years we were in the NIT. It's all fragile. It's humbling."

The team Florida beat in 2007, Ohio State, has undergone a similar rebuilding period, albeit for different reasons. Three freshman starters from that team (center Greg Oden and guards Mike Conley and Daequan Cook) turned pro after just one season. Subsequent centers Kosta Koufos and B.J. Mullens were one-and-dones, as well. Thankfully for Buckeyes coach Thad Matta, star guard Evan Turner opted to return for his junior season, and the Buckeyes -- after winning the NIT in 2008 and losing in the first round of the NCAA tournament last season -- have finally reloaded and are in contention for a deep tourney run this season.

BenHowland's Bruins have also been victimized by a string of one-and-dones. While their 2006-'08 run revolved around several key veterans (Aaron Afflalo, Darren Collison, Josh Shipp, and Luc Richard Mbah a Moute all played at least three seasons), two stars from that last team, center Kevin Love and guard Russell Westbrook, bolted after their only seasons as starters, as did last year's star freshman, Jrue Holiday. This year, the bottom finally fell out.

"It has definitely been a challenge when you are starting over again," Howland said.

Some say college basketball is in the midst of an age of parity, but it seems more a case of instability. Coaches at the highest level must not only recruit the best prospects but also be prepared for their potentially imminent departures. It's no coincidence that nearly all recent national championship teams -- from Williams' first title team in 2005 with Sean May, Raymond Felton and Rashad McCants -- were able to keep a core of stars together for at least three seasons.

John Calipari may be the one coach who's managed to exploit the sport's increasingly mercenary nature. With the import of one extraordinary class of freshmen, he's been able to transform Kentucky from an NIT team in 2009 to the nation's No. 1 team in 2010. Ironically, Calipari plucked the most important member of that class -- Raleigh, N.C., point guard John Wall -- from UNC's backyard. And point guard happens to be the Tar Heels' biggest weakness. (Williams declined to offer Wall a scholarship, purportedly due to a strained relationship with the player's AAU coach.)

It used to be UNC's rival, Duke, that set the standard for annual rebuilding -- out went Elton Brand, William Avery and Corey Maggette, in came Jason Williams, Carlos Boozer and Mike Dunleavy -- but it's now been six years since the Blue Devils have reached a Final Four. Over the past five years, the lone Final Four-level program to avoid even a one-year setback has been Kansas. Bill Self's 2008 championship team lost all five starters yet managed to follow up by winning the Big 12 again last season and currently sits No. 2 in the polls.

That Kansas team was so loaded that current All-America candidates SherronCollins and Cole Aldrich came off the bench. UNC had no such superstars waiting in the wings (though Davis, a sophomore, could still get there), and its most hyped incoming freshman, John Henson, wasn't physically ready to dominate the way the Tar Heels needed him to.

"Did I think [in the preseason] we were going to have ups and downs? Yes," Williams said. "Did I think we would have them in the manner that we're having? No."

Four years ago, the Tar Heels lost the top seven scorers from the previous season's title squad yet still managed to win 31 games and earn a No. 3 seed in the NCAA tournament. (They lost to George Mason in the second round.) Tyler Hansbrough led the team in scoring and rebounding as a freshman, while upperclassmen Reyshawn Terry and David Noel morphed from career role players to productive starters.

AP voters must have envisioned a similarly seamless transition when they bestowed such a lofty preseason ranking on these Tar Heels. Even if they rally over the next several weeks, it's hard to imagine they'll come anywhere close to reaching those expectations. Another stable of highly regarded recruits -- including Rivals.com's No. 2 player in the country, wingman Harrison Barnes -- will have to come to the rescue next winter.

There's no shame in suffering a down year. Not in this sport. If North Carolina can't maintain a dynasty, who can?