Human hedge funds are as bullish as their robot competitors -- ringing alarm bells at JPMorgan Chase & Co. As U.S. stocks flirt with all-time highs, evidence is building that fast-money investors have stretched positions with echoes of the January melt-up. Hedge funds pursuing long-short equity strategies have record exposure to the S&P 500 Index, judging by the portion of their returns attributable to the benchmark, a measure known as beta.