Editing Allopatric speciation (section)

=== Modes with secondary contact ===
{{See also|Ecological speciation}}
Ecological speciation can occur allopatrically, sympatrically, or parapatrically; the only requirement being that it occurs as a result of adaptation to different ecological or micro-ecological conditions.<ref>{{cite book|last=Nosil|first=P.|title=Ecological Speciation|year=2012|publisher=Oxford University Press|location=Oxford|isbn=978-0199587117|pages=280}}</ref> Ecological allopatry is a reverse-ordered form of allopatric speciation in conjunction with [[Reinforcement (speciation)|reinforcement]].<ref name="Johannesson2010"/> First, divergent selection separates a non-allopatric population emerging from pre-zygotic barriers, from which genetic differences evolve due to the obstruction of complete gene flow.<ref>{{Citation |title=Natural selection in action during speciation | author=Sara Via | journal=PNAS | year=2009 | volume=106 | issue= Suppl 1| pages=9939–9946 | doi=10.1073/pnas.0901397106| pmid=19528641 | pmc=2702801 | bibcode=2009PNAS..106.9939V | doi-access=free }}</ref> The terms allo-parapatric and allo-sympatric have been used to describe speciation scenarios where divergence occurs in allopatry but speciation occurs only upon secondary contact.<ref name="Speciation"/>{{rp|112}} These are effectively models of reinforcement<ref>{{Citation |title=Sympatric speciation in animals: new wine in old bottles | author=Guy L. Bush | journal=Trends in Ecology & Evolution | year=1994 | volume=9 | issue=8 | pages=285–288 | doi=10.1016/0169-5347(94)90031-0| pmid=21236856 | bibcode=1994TEcoE...9..285B }}</ref> or "mixed-mode" speciation events.<ref name="Johannesson2010"/>