how do allopatric and sympatric speciation differ? allopatric speciation involves a physical separation of groups as they form new species; sympatric speciation does not. allopatric speciation involves loss of gene flow between groups; sympatric speciation does not. allopatric speciation involves loss of reproductive compatibility between groups as they form new species; sympatric speciation does not. allopatric speciation involves genetic changes as groups form new species; sympatric speciation does not.