I've noticed that there has been many cross-over episodes involving One Piece and Toriko.
In fact, Toriko's first episode has One Piece characters in it.
Is there any kind of connection between both of the two series?
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Some possible reasons:
anime info: http://www.mahou.org/Showtime/?o=ET
manga info: http://en.wikipedia.org/wiki/Weekly_Shounen_Jump#Series
Year later at the 1st anniversary of Toriko and because of the success of the first collaboration, a second Toriko x One Piece Collaboration Special was announced. A 1 hour special serving as Episode 51 of Toriko and Episode 542 of One Piece.
A third collaboration special crossover was aired on April 7th, 2013, titled Dream 9 Toriko x One Piece x Dragon Ball Z Super Collaboration Special. A 1 hour special featuring characters from Toriko, One Piece and Dragon Ball Z and serving as Episode 99 of Toriko and Episode 590 of One Piece.