Who decides when Manga gets canceled and why and how?

I seriously had no idea how freakin cut-throat the manga process is. I heard that for Shonen Jump, you can be a popular manga for like 20 years, but if you are in the bottom rankings for I think 10 weeks straight, you are outta there, your manga is over, see ya, good bye, thanks for the memories, don't let the door hit your ass on the way out. And I even heard that mangas will be canceled in mid story. Now, that's not very unusual in American television, shows like Boss (Starring Kelsey Grammer) were cut despite looking like a great show. I mean, Television and Manga can be compared very similarly in a sense, you've gotta maintain viewer interest.

My question is basically, Since I've only just heard about this, I wanna hear your perspectives and stories and add more detail to this discussion and see if there is anything to add-on or disprove. Just add an opinion or "What you've heard" kind of stuff, etc. who decides when it's cut, why and how? Also, does it vary from certain magazines to another? Fairy Tail is one of the popular anime that isn't associated with Shonen Jump. Also maybe a discussion on the Japanese demographics and what trends appear in terms of what the average demographic desires.

Basically, It all depends on each magazines.

Shonen Jump is the most extreme example of the Japanese manga industry but is probably the most "transparent" in their decision making. (I'm going to talk about JUMP only, since it's the most transparent)

Before we speak about cancellations, here's how a newcomer gets serialized:
- Authors release a one-shot, they put it in one issue, and wait for the votes to come in. They usually do this with 2 or 3 new one shots.
From Issue #37/38 2013 (Double week issue), to issue #41 2013, Jump released 3 new one shots. (Ana no Mujina, Mochizuki, Tokudou!!)
But the number of "new series" are usually dependent on the number of canceled series. (From the same issue span, 1 series got canceled, which means normally only one would be serialized, but it's not strange if they didn't serialized any new one shots.

-For Cancellations, the criteria for getting cancelled in JUMP is simple, getting bad popularity rankings, regardless of the contents. Getting stuck on the 5 lowest for too long = the higher the possibility of cancellation.
But to make things easier for newcomers, they will get 7 free chapters from the start before they get "ranked", also getting a color page/center color/lead color means they are not "included" in the popularity rankings on that issue (another precious freebie).

The latest canceled manga "Smoky B.B" started on #26 ended on #41, Mutou Black started on #25 and ended on #36. After their first 7 chapters, both new series kept dwindling on the lower rankings.

-There's only one author that has a very special exception in Jump, which is the author of Hunter X Hunter, Togashi Yoshihiro.

-Authors can also end their mangas on their own, but this act is not well supported by the "Brass" because JUMP wants a long running series.

Besides JUMP, other manga magazines aren't that transparent on their decision making and mostly seems lenient seeing that there are series running for more than a decade. The longest running series that isn't from JUMP, is "Detective Conan" (Shonen Sunday), with 19 years of content.
Fairy Tail is also in Shonen Sunday, along with Hayate no Gotoku, Zettai Karen Children. It was also home to Air Gear, Inuyasha and Ranma 1/2

There are a lot of other manga magazines.
http://en.wikipedia.org/wiki/List_of_manga_magazines

Discussions about contents from Shonen JUMP
http://weeklyjump.livejournal.com/

About demographic trends, you need to work or have a close friend in those companies to get such information. But each magazine has their own target demographic, Shonen Jump and Sunday with Shonens (Male, Elementary Age to 15 years old). Young Jump, Young Animal, and Young Ace with Seinens. (Male, Age 18 to 30). And there's Shoujo and Josei the gender opposites.

If authors can end their own series, then why is Bleach still running? I heard Kubo wanted to end Bleach, but couldn't because he was under contract.

They get pressured to. You can read Bakuman if you want to know how Jump system works. It's a manga series about the making and serialization system of the Jump world. I'm pretty sure I'm making it sound dull, but it really isn't.

That was going to be another question I wanted to bring up, I heard that they forced Tite Kubo to hurry up and end Bleach because the manga was doing very poorly, in fact this topic was inspired by Bleach's ending soon

we call all agree that it "could" have ended at the espada arc


on a side note could we add in ... ( why they make a anime version before the manga is past 100 .. or is done )

Dead man wonder land as an example

Well I read Bakuman and I was under the impression that authors couldn't end the series on their own.

It's possible.
Bakuman the manga itself is one prime example where they actually end the manga with the same philosophical message that they put into their manga "finish the manga when it's at the highest point". Another example, even on a downer note was "Kagami no Kuni Harisugawa", where the author decided to end it because the author already saw that it's impossible to develop the story with that kind of idea and setting, even though it got so-so rankings.