Jaguar gets the last slot on purpose. Its the series that gets next to Jaguar that pretty much next on the chopping block.
Usually, if a longer running series is at the bottom of the rankings for a while, then they get the signal to go…particularly if they are nearing the end of their run anyway.
As for who's next, there are a few series that are either weak now or closing in on a termination point. My notables:
-Bo-bobo: It hasn't been as hot as it was when it first started, but I think Sawai is starting to wrap things up anyway from recent story suggestions.
! Baldy-Bald the Third pretty much has declared one final war against anyone against him, including former allies and fist users, and Bo-bobo's team has come together one last time to put a stop to him. They could somehow still go with revealing Bababa-ba Ba-baba if they want to do more story after this, but I think once they beat the Third (now powered with Bi-bibi's Hair Ball), that's it.
-Prince of Tennis: It seems like there is one final match left and it has been at bottom a few times..but the yaoi fans probably don't want to let it go
-Eyeshield 21: This is really popular, but with recent events I don't know what they could do.
! They are nearing the end of the semi-final game with Ojo and the game after this, if Deimon wins, is the Christmas Bowl itself. Since these Kanto games starting with Shinryuji have been a half-year each, I could probably see a half-year for the Christmas Bowl and that's it. Sure people will complain that they could have "another year", but it probably wouldn't be as fun.
-D.Gray-Man: Low rankings, enemies being stopped…I don't know if this will last too much longer but I never followed the series so I can't say.
-P2!: This series has been the "little series that could", but that means nothing if several stronger new series comes along and bump it out.
I wish I could add Naruto and Bleach to the list, but odds are that Kishimoto and Kubo will stall it out for all its worth.