▁regarding ▁this ▁process : ▁ 1 ) ▁differential ▁fusion , ▁which ▁suggests ▁that ▁only ▁populations ▁with ▁a ▁keen ▁ability ▁to ▁disc rim inate ▁between ▁species ▁will ▁persist ▁in ▁sym pat ry ; ▁and ▁ 2 ) ▁character ▁disp lacement , ▁which ▁implies ▁that ▁distingu ishing ▁characteristics ▁will ▁be ▁height ened ▁in ▁areas ▁where ▁the ▁species ▁co - oc cur ▁in ▁order ▁to ▁facil itate ▁disc rim ination . ▁ ▁Rein for cement ▁Rein for cement ▁is ▁the ▁process ▁by ▁which ▁natural ▁selection ▁rein for ces ▁re product ive ▁isol ation . ▁In ▁sym pat ry , ▁rein for cement ▁increases ▁species ▁disc rim ination ▁and ▁sexual ▁adaptation ▁in ▁order ▁to ▁avoid ▁mal ada pt ive ▁hy brid ization ▁and ▁encou rage ▁spe ci ation . ▁If ▁hy brid ▁off spring ▁are ▁either ▁ster ile ▁or ▁less - fit ▁than ▁non - hy brid ▁off spring , ▁m ating ▁between ▁members ▁of ▁two ▁different ▁species ▁will ▁be ▁selected ▁against . ▁Natural ▁selection ▁decre ases ▁the ▁probability ▁of ▁such ▁hy brid ization ▁by ▁selecting ▁for ▁the ▁ability ▁to ▁identify ▁m ates ▁of ▁one ' s ▁own ▁species ▁from ▁those ▁of ▁another ▁species . ▁ ▁Re product ive ▁character ▁disp lacement ▁Re product ive ▁character ▁disp lacement ▁strength ens ▁the ▁re product ive ▁bar riers ▁between ▁sym pat ric ▁species ▁by ▁encourag ing ▁the ▁diver gence ▁of ▁tra its ▁that ▁are ▁cru cial ▁to ▁reprodu ction . ▁D iver gence ▁is ▁frequently ▁distinguished ▁by ▁ass ort ative ▁m ating ▁between ▁individuals ▁of ▁the ▁two ▁species .