Hedge fund mogul William Ackman, one of last year’s best performers, joined a string of high profile managers in reporting deep losses for August as global markets tumbled amid fears over slower growth in China. Ackman’s Pershing Square Capital Management, which makes concentrated bets on a small number of stocks, told clients on Wednesday that its Pershing Square LP fund fell 7.7 percent last month, leaving it flat on the year with a 0.06 percent gain.