Mario Cibelli of Marathon Capital Management sold his stake in GAMCO Investors Inc. , a Rye, New York-based provider of investment advisory services where Cibelli once provided back-office support to the trading desk, in the fourth quarter. Cibelli's fourth-quarter activity primarily consisted of additions to existing stakes, and his most significant such transaction was the 77% increase in his stake in GrubHub Inc. , a Chicago-based online food-ordering company.