And then there was one: Jackson alone on ‘American Idol’

Jennifer Lopez is the second judge in two days to say she’s leaving “American Idol.”

Her representative, Mark Young, said Friday that Miss Lopez is ending her time on television’s most popular show after two years. Aerosmith’s Steven Tyler said the same thing on Thursday.

Miss Lopez broke the news to “Idol” host Ryan Seacrest on his radio show.

“I really was dreading this phone call with you,” she told him. “I honestly feel like the time has come that I have to get back to doing the other things that I do that I’ve put kind of on hold because I love ’Idol’ so much.”

That means the show’s judging panel is down to one, Randy Jackson, and there are reports that he may take a different role on the program moving forward.

It’s an adolescent identity crisis for “American Idol,” which has been TV’s most popular program for nearly a decade. Ratings for the Fox show have declined as TV’s talent-show field gets more competitive.

When the show returns for its 12th season in January, it will have to be a re-engineered version of the once-powerhouse series that turned hopefuls such as Jennifer Hudson into stars and gave network rivals fits.

Mr. Tyler started the exodus with his announcement Thursday that he was putting rock ’n’ roll ahead of the show, which he said had been “over-the-top fun.”

“I strayed from my first love, Aerosmith, and I’m back — but instead of begging on my hands and knees, I got two fists in the air, and I’m kicking the door open with my band,” Mr. Tyler said in a statement. Aerosmith is on a nationwide tour with Mr. Tyler and has an album due out in the fall.

In a phone interview Thursday with the Associated Press as the news about Mr. Tyler broke, Miss Lopez said she was saddened to hear that he was leaving and added that his departure would play a role in her decision.

“I can’t even imagine anyone else there right now because I’ve just spent two years sitting next to him,” she said. “I love Steven, and we became close during that time. We were a great support for each other, on an adventure that neither one of us knew what it was going to be. So it’s hard to hear that he won’t be doing it.”

Mr. Jackson and his “Dawg!” exclamations have been stalwart parts of “Idol.” But the show’s multiyear contracts, such as the one Mr. Jackson signed, typically include an escape clause that the network can choose to exercise or not.

A call to Mr. Jackson’s representative was not returned. Fox declined to make an executive available to discuss the show and its judges, but one expressed measured regret in a statement on Mr. Tyler’s decision in a statement.

“We are very sad that Steven has chosen to focus more on his music, but we always knew when we hired a rock ’n’ roll legend, he would go back to his music,” said Mike Darnell, the network’s president of alternative entertainment.

Speculation about potential new panelists has focused on Mariah Carey, with former “Idol” runner-up Adam Lambert getting a shout-out from his fans. Much is at stake for the show and for its judges: Miss Lopez’s contract reportedly was worth $12 million, and the stint proved a career-booster for her.

Mr. Seacrest, the other original cast member, will provide a stable center. He signed a two-year contract with “American Idol” producers in the spring to continue as host.

The Fox series, which began with Mr. Jackson, Simon Cowell and Paula Abdul as judges, has made changes on the panel over the years. Ellen DeGeneres joined one season, and songwriter Kara DioGuardi was added as a fourth judge to work with Mr. Jackson, Mr. Cowell and Miss Abdul.

The addition of Mr. Tyler and Miss Lopez two years ago added fresh star power, and the pair and Mr. Jackson clicked on camera.

But “American Idol” ended up in a vulnerable position, coming off a May finale that drew 21.5 million viewers as Phillip Phillips was crowned the newest winner.

It was a record low finish and followed a pattern of declining viewership for the once inevitably top-rated series, not to mention a pattern of “white guys with guitars,” as fans describe the show’s recent string of similar winners.

The series ended the 2011-12 season as No. 2 with an average 20 million viewers for the Wednesday performance episodes, just edging third-place “CSI” (19.7 million) on CBS and ABC’s top-rated “Sunday Night Football” (20.7 million).

“Idol” still rules among the most-watched talent shows, topping ABC’s “Dancing With the Stars” and NBC’s “The Voice.” But it is fighting to keep advertiser-favored young viewers, with “The Voice” nearly equaling its audience among adults 18 to 49.

Fox, which from the start has protected “Idol” by programming it just once a year, has diluted its uniqueness with a family competitor, Mr. Cowell’s “The X Factor,” which debuted last fall. After a disappointing start, the show underwent its own judges’ shakeup to add Demi Lovato and Britney Spears.

“American Idol” hasn’t been helped by a run of champions who have failed to achieve the career sizzle of Miss Hudson, Carrie Underwood or Kelly Clarkson.

The winner, however, ultimately is up to the audience. The judges are in the network’s and producers’ control, and their next moves are critical ones.

• AP Television Writer David Bauder and AP Music Editor Nekesa Mumbi Moody in New York contributed to this report.