The next few months likely will be dominated by news about some of the biggest reality competitions on television — and not who is going to win them, but who is going to be sitting at the judges’ tables.

For instance, “American Idol,” fresh off its weakest season, has dropped Randy Jackson, Mariah Carey and Nicki Minaj and added Jennifer Hudson. Keith Urban is expected to leave soon, and multiple reports have two more former contestants signing on: Kelly Clarkson and either Clay Aiken or Adam Lambert.

And “Dancing with the Stars,” already planning to shrink to one night a week in the fall, could make an even bigger change by shaking up its aboriginal crew of Carrie Ann Inaba, Len Goodman and Bruno Tonioli. All three have contracts that expire before next season.

Already, “The Voice” has announced that it would bring back Christina Aguilera and Cee Lo Green in the fall, setting up a rotating panel of regulars. “The X Factor,” still trying to find a combination that works, just hired Kelly Rowland and Latin music star Paulina Rubio to team up with Simon Cowell and Demi Lovato.

The stakes behind the changes are big. For the judges, of course, who earn gigantic sums for their work. (Carey earned a reported $18 million for her single season of work on “American Idol.) But it is even a bigger issue for the networks that air the shows.

For the past decade, reality competitions have been huge moneymakers, but most of them are fading in the ratings. Sure, ratings are down everywhere, but these shows are getting hit harder than most.

“American Idol,” which once produced more than $800 million in annual ad revenue for Fox, just capped its worst ratings season ever. How bad? None of the show’s previous 11 finales had failed to draw more than 20 million viewers; season 12′s pulled in 14.7 million.

“Dancing with the Stars,” ABC’s most popular show, lost nearly 30 percent of its viewers under 50 this spring. “The X Factor” lost almost a third of its audience from season one to season two.

Rather than retooling their shows or putting more effort into their contestant searches, the producers are aiming their attention at putting together all-star arrays of judges. For this, we can credit — or blame — “The Voice.”

NBC’s show has avoided the ratings sag, more or less, to emerge as the top non-sports show among the under-50 viewers that advertisers prefer. “The Voice” features four judges — the current set is Adam Levine, Blake Shelton, Shakira and Usher — all of whom are big contemporary stars: no has-beens or behind-the-curtain types. And more than any show, the judges are the stars. They put together and coach teams of singers, compete with each other and perform weekly.

The contestants are pretty much an afterthought. Unlike “American Idol,” which has produced several major and minor stars, the winners and runners-up on “The Voice” generally recede into anonymity when their season is over.

And so “The Voice” model is being replicated on all levels.

First, everyone is going to four judges, at least. “American Idol” made the jump from three to four last season (after going from four to three two years before that). “America’s Got Talent,” NBC’s perennial No. 1 summer show, has made the shift for the season that debuted earlier this month. Sharon Osbourne, who left in a dispute with the network, has been replaced by two judges: Heidi Klum and former Spice Girl Mel B.

“Dancing with the Stars,” even if it keeps its current lineup of judges, is expected to add a fourth in the fall.

And shows are trying to amp up the star power, too — although that comes with no guarantee. Britney Spears brought a ton of media interest when she signed on with “The X Factor” last year (for a mere $12 million), but the viewers didn’t tune in, and — belying her personal life — proved to be a dull figure in the judge’s chair.

One thing the quartet of “The Voice” possesses that other shows have found difficult to buy is chemistry. That crew — Shelton and Levine in particular — mesh well with each other and seem relaxed and natural on camera. It’s a quality that the original “American Idol” crew had, and that helps shows like “Project Runway” and “Top Chef” stand out.