Actor Leonardo DiCaprio, the star of the new film "The Great Gatsby," and his foundation have teamed up with Christie's for a charity auction next week to benefit environmental causes. Thirty-three works, many created for and donated to the auction by some of the world's top artists, will go under the hammer on Monday in New York at The 11th Hour Auction, which aims to raise as much as $18 million to protect the last wild places on Earth and their endangered species. "A lot of the works of this quality have never been at auction. We have what we believe are conservative estimates," Loic Gouzer, international specialist at Christie's and the head of the sale, said in an interview. "It is going to be the biggest one-time environmental fundraiser ever," he added. Zeng Fanzhi's "The Tiger," an oil on canvas, Bharti Kher's "The Skin Speaks a Language Not Its Own," a work on fiberglass, and Mark Grotjahn's &qu