The nation’s largest MBS-investing real estate investment trust, Annaly Capital Management, this week agreed to buy the third largest player in the market, setting off speculation among analysts and investors that the “mREIT” sector could be in for a healthy dose of consolidation. The New York-based Annaly said it would buy Hatteras Financial Corp., Winston-Salem, NC, for roughly $1.5 billion in cash and stock. At year end, Annaly ranked...