Before revision: In a vacancy chain, a new resource unit that arrives into a population is taken by the first individual in line, who then leaves his/her old unit behind, this old unit is taken by a second individual, leaving his/her old unit behind, and so forth.
After revision: In a vacancy chain, a new resource unit that arrives into a population is taken by the first individual in line, who then leaves their old unit behind, this old unit is taken by a second individual, leaving their old unit behind, and so forth.