After less than a year on the job, MySpace CEO Owen Van Natta has stepped down from the position. Last April, Van Natta replaced MySpace founder Chris DeWolfe,, who was ousted from the position as part of a management shakeup designed to reinvigorate the struggling social networking service.

MySpace did not name a replacement, but rather has elevated chief product officer Jason Hirschhorn and COO Mike Jones to the positions of co-presidents. They will both report to Jon Miller, Chairman and CEO of digital media for MySpace parent company NewsCorp.

Speculation over the reason for Van Natta’s departure has already begun. AllThingsD reports he was actually fired by Miller, who had been taking a more active role in trying to fix MySpace's problems amid tension between Van Natta and his top two executives.

TechCrunch says Van Natta and Miller didn’t get along. Miller hired Hirschhorn, but Van Natta wanted him fired. TechCrunch last week reported that it was Hirschhorn who was on his way out, but that’s obviously no longer the case.

Meanwhile, PaidContent posted the internal memo from Miller announcing the move, which notes that the changes will have no affect on MySpace’s media-oriented vision:

While this may be a surprising turn of events for some of you, I am absolutely confident that this change is best for all parties involved and – most importantly – the MySpace business. Owen took on an incredible challenge in assuming leadership of MySpace during a difficult period. He has worked to refocus and revitalize the company, and I believe MySpace is pointed in the right direction and gaining valuable momentum – we added over 1.5 million users and grew significantly in time spent last month – as a result of many of his efforts. However, in discussing with Owen his priorities for the future both personally and professionally, we both agreed that it was best that he step down at this time. I am grateful to Owen for his hard work, and I ask that you join me in wishing him well in the future. His departure is effective immediately, as are the appointments of both Mike and Jason.

MySpace has lost significant ground to rival Facebook in recent years. MySpace slipped in all key metrics—including monthly unique visitors, registered users, and time spent per use—and now trails Facebook in both the U.S. and internationally. Last June, the company slashed 30% of its workforce.

The strategy to turn this around is a renewed focus on making MySpace a social entertainment hub. Van Natta during his brief tenure was charged with overseeing that strategy, with Hirschhorn and Jones left to driving the execution. Based on the memo, it seems that strategy will not change. Rather, Miller instead is taking on the oversight of the execution.

The change in executive structure does not seem to have affected MySpace Music or that of MySpace Music president Courtney Holt.

A mere three weeks ago, Van Natta spoke at MIDEM as part of his first international tour as MySpace CEO—a trip that included a stop at the World Economic Forum in Davos, indicating he may not have been about to quit.