What exactly would count as copyright infringement in a replication paper?
After asking permission to Elsevier (I'm editor in chief for ReScience), they confirmed (in this specific case) that equations can be re-used without asking permission to Elsevier:


  Our Global Rights group has confirmed that these equations are not
  copyrighted;  therefore, you can merely acknowledge the 2012 Journal
  of Theoretical Biology as the source of the equations but do not
  require written permission from Elsevier.