Daniel Murphy is one of Ike Davis’ closest friends on the Mets, and has been one of Davis’ staunchest supporters during his struggles at the plate this season and last season. He also apparently will be the struggling slugger’s replacement at first base, at least for the time being. One day after the Mets optioned Davis to Class AAA Las Vegas, general manager Sandy Alderson indicated during a radio interview that Murphy was the Mets’ “first option” to play first base in Davis’ absence, at least temporarily. The Mets continue their homestand tonight with the first of three games against NL Central-leading St. Louis. Murphy, who had struggled in the field when he first came to the big leagues, has found a home at second base and has worked hard to make himself into a respectable defensive player — a costly 10th-inning error in Sunday’s loss to the Marlins notwithstanding. However, in his interview with WFAN on Monday, Alderson indicated this would be a “temporary” move, and it was designed to give the Mets a chance to look at Jordany Valdespin at second base. Because of Murphy’s presence, the 25-year-old Valdespin has played mostly in the outfield, which is not considered his natural position. He is talented but erratic, and his flamboyant approach to the sport often has vexed manager Terry Collins, who lectured him Sunday after Valdespin was caught stealing third for the final out of the first inning with Murphy at the plate. Murphy said recently he would be willing to play “wherever” Collins wanted should Davis be demoted.