▁until ▁a ▁new ▁species ▁is ▁introduced ▁into ▁the ▁system , ▁which ▁breaks ▁down ▁existing ▁species ▁bar riers . ▁An ▁example ▁is ▁the ▁introduction ▁of ▁the ▁Spanish ▁sl ug ▁in ▁Northern ▁Europe , ▁where ▁inter bre eding ▁with ▁the ▁local ▁black ▁sl ug ▁and ▁red ▁sl ug , ▁which ▁were ▁tradition ally ▁considered ▁clearly ▁separate ▁species ▁that ▁did ▁not ▁inter bre ed , ▁shows ▁that ▁they ▁may ▁be ▁actually ▁just ▁sub species ▁of ▁the ▁same ▁species . ▁ ▁Where ▁closely - related ▁species ▁co - exist ▁in ▁sym pat ry , ▁it ▁is ▁often ▁a ▁particular ▁challenge ▁to ▁understand ▁how ▁the ▁similar ▁species ▁persist ▁without ▁out comp eting ▁each ▁other . ▁N iche ▁partition ing ▁is ▁one ▁mechanism ▁invoked ▁to ▁explain ▁that . ▁Indeed , ▁studies ▁in ▁some ▁species ▁complex es ▁suggest ▁that ▁species ▁diver gence ▁have ▁gone ▁in ▁par ▁with ▁e colog ical ▁different iation , ▁with ▁species ▁now ▁prefer ring ▁different ▁micro hab itats . ▁Similar ▁methods ▁also ▁found ▁that ▁the ▁Amazon ian ▁f rog ▁Ele uther od act yl us ▁o ck enden i ▁is ▁actually ▁at ▁least ▁three ▁different ▁species ▁that ▁diver ged ▁over ▁ 5 ▁million ▁years ▁ago . ▁ ▁A ▁species ▁f lock ▁may ▁arise ▁when ▁a ▁species ▁pen etr ates ▁a ▁new ▁ge ographical ▁area ▁and ▁divers ifies ▁to ▁occup y ▁a ▁variety ▁of ▁e colog ical ▁nich es , ▁a ▁process ▁known ▁as ▁adapt ive ▁radiation . ▁The ▁first ▁species ▁f lock ▁to ▁be ▁recognized ▁as ▁such ▁was ▁the ▁ 1 3 ▁species ▁of ▁Dar win