Editing Allopatric speciation (section)

== Observational evidence ==
{{see also|Peripatric speciation#Evidence}}
{{multiple image
| direction         = vertical
| width             = 300
| image1            = Areas of Endemism (South America).png
| caption1          = [[South America]]'s areas of [[endemism]]; separated largely by major rivers.
| image2            = Area Cladogram of Charis butterflies (Horizontal).png
| caption2          = A cladogram of species in the ''[[Charis (butterfly)|Charis cleonus]]'' group superimposed over a map of South America showing the biogeographic ranges or each species
}}
As allopatric speciation is widely accepted as a common mode of speciation, the scientific literature is abundant with studies documenting its existence. The biologist [[Ernst Mayr]] was the first to summarize the contemporary literature of the time in 1942 and 1963.<ref name="Speciation"/>{{rp|91}} Many of the examples he set forth remain conclusive; however, modern research supports geographic speciation with molecular phylogenetics<ref name=BarracloughVogler2000>{{Citation |title=Detecting the Geographical Pattern of Speciation from Species-Level Phylogenies | author=Timothy G. Barraclough| author2=Alfried P. Vogler | journal=American Naturalist | year=2000 | volume=155 | issue=4 | pages=419–434 | doi= 10.2307/3078926| jstor=3078926| pmid=10753072}}</ref>—adding a level of robustness unavailable to early researchers.<ref name="Speciation"/>{{rp|91}} The most recent thorough treatment of allopatric speciation (and speciation research in general) is [[Jerry Coyne]] and [[H. Allen Orr]]'s 2004 publication ''Speciation''. They list six mainstream arguments that lend support to the concept of vicariant speciation:
*Closely related species pairs, more often than not, reside in geographic ranges adjacent to one another, separated by a geographic or climatic barrier.
*Young species pairs (or sister species) often occur in allopatry, even without a known barrier.
*In occurrences where several pairs of related species share a range, they are distributed in abutting patterns, with borders exhibiting [[Hybrid zone|zones of hybridization]].
*In regions where geographic isolation is doubtful, species do not exhibit sister pairs.
*Correlation of genetic differences between an array of distantly related species that correspond to known current or historical geographic barriers.
*Measures of reproductive isolation increase with the greater geographic distance of separation between two species pairs. (This has been often referred to as [[Isolation by distance|reproductive isolation by distance]].<ref name="Modes and Mechanisms of Speciation" />)

=== Endemism ===
{{See also|Insular biogeography|Elevational diversity gradient}}
Allopatric speciation has resulted in many of the biogeographic and biodiversity patterns found on Earth: on islands,<ref>{{Citation | title=Island Biogeography: Ecology, Evolution, and Conservation | edition=2 | author=Robert J. Whittaker | author2=José María Fernández-Palacios | date=2007 | publisher=Oxford University Press }}</ref> continents,<ref>{{Citation |title=Large-scale processes and the Asian bias in species diversity of temperate plants | author=Hong Qian | author2=Robert E. Ricklefs | journal=Nature | year=2000 | volume=407 | issue= 6801| pages=180–182 | doi= 10.1038/35025052| pmid=11001054 | bibcode=2000Natur.407..180Q | s2cid=4416820 }}</ref> and even among mountains.<ref name=MJSetal2016>{{Citation |title=Topography-driven isolation, speciation and a global increase of endemism with elevation  | author=Manuel J. Steinbauer| author2=Richard Field| author3=John-Arvid Grytnes|author4=Panayiotis Trigas|author5=Claudine Ah-Peng|author6=Fabio Attorre|author7=H. John B. Birks|author8=Paulo A. V. Borges|author9=Pedro Cardoso|author10= Chang-Hung Chou|author11=Michele De Sanctis| author12=Miguel M. de Sequeira| author13=Maria C. Duarte| author14=Rui B. Elias| author15=José María Fernández-Palacios| author16=Rosalina Gabriel| author17=Roy E. Gereau| author18=Rosemary G. Gillespie| author19=Josef Greimler| author20=David E. V. Harter| author21=Tsurng-Juhn Huang| author22=Severin D. H. Irl| author23=Daniel Jeanmonod| author24=Anke Jentsch| author25=Alistair S. Jump| author26=Christoph Kueffer| author27=Sandra Nogué| author28=Rüdiger Otto| author29=Jonathan Price| author30=Maria M. Romeiras| author31=Dominique Strasberg| author32=Tod Stuessy| author33=Jens-Christian Svenning| author34=Ole R. Vetaas| author35=Carl Beierkuhnlein | journal=Global Ecology and Biogeography | year=2016 | volume=25 | issue= 9| pages=1097–1107 | doi=10.1111/geb.12469 | bibcode=2016GloEB..25.1097S| hdl=1893/23221| url=http://eprints.nottingham.ac.uk/34319/1/Submitted%20version%20R3%20March%2016.pdf| hdl-access=free}}</ref>

Islands are often home to species [[endemism|endemics]]—existing only on an island and nowhere else in the world—with nearly all taxa residing on isolated islands [[Common descent|sharing common ancestry]] with a species on the nearest continent.<ref name="JPrice2008">{{Citation | title=Speciation in Birds | author=Trevor Price | date=2008  | pages=1–64 | publisher=Roberts and Company Publishers | isbn=978-0-9747077-8-5 }}</ref> Not without challenge, there is typically a correlation between island endemics and [[Biodiversity|diversity]];<ref>{{Citation |title=Speciation and Endemism under the Model of Island Biogeography | author=Xiao-Yong Chen | author2=Fangliang He | s2cid=24127933 | journal=Ecology | year=2009 | volume=90 | issue=1 | pages=39–45 | doi= 10.1890/08-1520.1| pmid=19294911 | bibcode=2009Ecol...90...39C }}</ref> that is, that the greater the diversity (species richness) of an island, the greater the increase in endemism.<ref>{{Citation |title=Ecology: Is speciation driven by species diversity? | author=Carlos Daniel Cadena| author2=Robert E. Ricklefs| author3= Iván Jiménez| author4=Eldredge Bermingham | journal=Nature | year=2005 | volume=438 | issue= 7064| pages= E1–E2| doi=10.1038/nature04308 | pmid=16267504| bibcode=2005Natur.438E...1C| s2cid=4418564}}</ref> Increased diversity effectively drives speciation.<ref>{{Citation |title=Species diversity can drive speciation | author=Brent C. Emerson | author2=Niclas Kolm | journal=Nature | year=2005 | volume=434 | issue= 7036| pages=1015–1017 | doi=10.1038/nature03450 | pmid=15846345 | bibcode=2005Natur.434.1015E | s2cid=3195603 }}</ref> Furthermore, the number of endemics on an island is directly correlated with the relative isolation of the island and its area.<ref name="JPrice2008-2">{{Citation | title=Speciation in Birds | author=Trevor Price | date=2008  | pages=141–155 | publisher=Roberts and Company Publishers | isbn=978-0-9747077-8-5 }}</ref> In some cases, speciation on islands has occurred rapidly.<ref>{{Citation |title=Analysis of an evolutionary species±area relationship | author=Jonathan B. Losos | author2=Dolph Schluter | journal=Nature | year=2000 | volume=408 | issue=6814 | pages=847–850 | doi= 10.1038/35048558| pmid=11130721 | bibcode=2000Natur.408..847L | s2cid=4400514 }}</ref>

Dispersal and ''in situ'' speciation are the agents that explain the origins of the organisms in Hawaii.<ref name="PriceWagner2004">{{Citation |title=Speciation in Hawaiian Angiosperm Lineages: Cause, Consequence, and Mode  | author=Jonathan P. Price | author2=Warren L. Wagner | journal=Evolution | year=2004 | volume=58 | issue=10 | pages=2185–2200 | doi= 10.1554/03-498| pmid=15562684 | s2cid=198157925 }}</ref> Various geographic modes of speciation have been studied extensively in Hawaiian biota, and in particular, [[angiosperm]]s appear to have speciated predominately in allopatric and [[parapatric speciation|parapatric]] modes.<ref name="PriceWagner2004"/>

Islands are not the only geographic locations that have endemic species. South America has been studied extensively with its [[areas of endemism]] representing assemblages of allopatrically distributed species groups. [[Charis (butterfly)|''Charis'' butterflies]] are a primary example, confined to specific regions corresponding to phylogenies of other species of butterflies, [[amphibian]]s, birds, [[marsupial]]s, [[primate]]s, [[reptile]]s, and [[rodent]]s.<ref name=HallHarvey2002>{{Citation |title=The Phylogeography of Amazonia Revisited: New Evidence from Riodinid Butterflies | author=Jason P. W. Hall | author2=Donald J. Harvey | journal=Evolution | year=2002 | volume=56 | issue=7 | pages=1489–1497 | doi= 10.1554/0014-3820(2002)056[1489:tpoarn]2.0.co;2| pmid=12206248 | s2cid=198157398 }}</ref> The pattern indicates repeated vicariant speciation events among these groups.<ref name=HallHarvey2002/> It is thought that rivers may play a role as the geographic barriers to ''Charis'',<ref name="Speciation"/>{{rp|97}} not unlike the [[river barrier hypothesis]] used to explain the high rates of diversity in the [[Amazon basin]]—though this hypothesis has been disputed.<ref>{{Citation |title=Most species are not limited by an Amazonian river postulated to be a border between endemism areas |first1=Sergio |last1=Santorelli Jr |first2=William E.|last2= Magnusson|first3= Claudia P.|last3= Deus |journal=Scientific Reports |year=2018 |volume=8 |issue=2294 |pages= 2294|doi=10.1038/s41598-018-20596-7 |pmid=29396491 |pmc=5797105 |bibcode=2018NatSR...8.2294S }}</ref><ref>{{Citation|title=Moving beyond the riverine barrier vicariant paradigm |author=Luciano N. Naka and Maria W. Pil |journal=Molecular Ecology |year=2020 |volume=29 |issue=12 |pages=2129–2132 |doi=10.1111/mec.15465 |pmid=32392379 |doi-access=free |bibcode=2020MolEc..29.2129N }}</ref> Dispersal-mediated allopatric speciation is also thought to be a significant driver of diversification throughout the [[Neotropical realm|Neotropics]].<ref>{{Citation |title=The drivers of tropical speciation | author=Brian Tilston Smith| author2=John E. McCormack| author3=Andrés M. Cuervo| author4=Michael. J. Hickerson| author5=Alexandre Aleixo| author6=Carlos Daniel Cadena| author7=Jorge Pérez-Emán| author8= Curtis W. Burney| author9=Xiaoou Xie| author10=Michael G. Harvey| author11=Brant C. Faircloth| author12=Travis C. Glenn| author13=Elizabeth P. Derryberry| author14=Jesse Prejean| author15=Samantha Fields| author16=Robb T. Brumfield | journal=Nature | year=2014 | volume=515 | issue=7527| pages=406–409 | doi=10.1038/nature13687 | pmid=25209666| bibcode=2014Natur.515..406S| s2cid=1415798| url=https://digitalcommons.lsu.edu/cgi/viewcontent.cgi?article=1519&context=biosci_pubs}}</ref>

[[File:Allopatric speciation caused by topography.svg|left|thumb|upright=1.7|Allopatric speciation can result from mountain topography. Climatic changes can drive species into altitudinal zones—either valleys or peaks. Colored regions indicate distributions. As distributions are modified due to the change in suitable habitats, reproductive isolation can drive the formation of a new species.]]
Patterns of increased endemism at higher elevations on both islands and continents have been documented on a global level.<ref name=MJSetal2016/> As topographical elevation increases, species become isolated from one another;<ref>{{Citation |title=Are mountain passes higher in the tropics? Janzen's hypothesis revisited | author=C. K. Ghalambor| author2= R. B. Huey| author3=P. R. Martin| author4=J. T. Tewksbury| author5=G. Wang | journal=Integrative and Comparative Biology | year=2014 | volume=46 | issue= 1| pages=5–7 | doi= 10.1093/icb/icj003| pmid=21672718| doi-access=free}}</ref> often constricted to [[Grade (slope)|graded]] zones.<ref name=MJSetal2016/> This isolation on "mountain top islands" creates barriers to gene flow, encouraging allopatric speciation, and generating the formation of endemic species.<ref name=MJSetal2016/> Mountain building ([[orogeny]]) is directly correlated with—and directly affects biodiversity.<ref>{{Citation |title=Biodiversity from mountain building | author=Carina Hoorn| author2=Volker Mosbrugger| author3=Andreas Mulch| author4=Alexandre Antonelli | journal=Nature Geoscience | year=2013 | volume=6 | issue= 3| pages=154 | doi= 10.1038/ngeo1742| url=https://pure.uva.nl/ws/files/1737504/135200_Nature_20Geoscience_20Hoorn.pdf| bibcode=2013NatGe...6..154H| doi-access=free}}</ref><ref>{{Citation |title=The Role of Mountain Ranges in the Diversification of Birds | author=Jon Fjeldså| author2=Rauri C.K. Bowie| author3=Carsten Rahbek | s2cid=85868089| journal=Annual Review of Ecology, Evolution, and Systematics | year=2012 | volume=43 | pages=249–265 | doi=10.1146/annurev-ecolsys-102710-145113 }}</ref> The formation of the [[Himalayas|Himalayan]] mountains and the [[Tibetan Plateau|Qinghai–Tibetan Plateau]] for example have driven the speciation and diversification of numerous plants and animals<ref>{{Citation |title=Uplift-driven diversification in the Hengduan Mountains, a temperate biodiversity hotspot | author=Yaowu Xing | author2=Richard H. Ree | journal=PNAS | year=2017 | volume=114 | issue=17 | pages=3444–3451 | doi=10.1073/pnas.1616063114 | pmid=28373546 | pmc=5410793 | bibcode=2017PNAS..114E3444X | doi-access=free }}</ref> such as ''[[Lepisorus]]'' ferns;<ref>{{Citation |title=The rise of the Himalaya enforced the diversification of SE Asian ferns by altering the monsoon regimes | author=Li Wang| author2=Harald Schneider| author3=Xian-Chun Zhang| author4= Qiao-Ping Xiang | journal=BMC Plant Biology | year=2012 | volume=12 | issue=210 | pages=1–9 | doi= 10.1186/1471-2229-12-210| pmid=23140168| pmc=3508991| doi-access=free}}</ref> glyptosternoid fishes ([[Sisoridae]]);<ref>{{Citation |title=The uplift of Qinghai-Xizang (Tibet) Plateau and the vicariance speciation of glyptosternoid fishes (Siluriformes: Sisoridae) | author=Shunping He| author2=Wenxuan Cao| author3= Yiyu Chen | journal=Science in China Series C: Life Sciences | year=2001 | volume=44 | issue=6 | pages= 644–651| doi= 10.1007/bf02879359| pmid=18763106| s2cid=22432209| url=http://ir.ihb.ac.cn/handle/152342/9866}}</ref> and the ''[[Rana chensinensis]]'' species complex.<ref>{{Citation |title=Speciation in the ''Rana chensinensis'' species complex and its relationship to the uplift of the Qinghai–Tibetan Plateau | author=Wei-Wei Zhou| author2=Yang Wen| author3=Jinzhong Fu| author4=Yong-Biao Xu| author5=Jie-Qiong Jin| author6=Li Ding| author7=Mi-Sook Min| author8=Jing Che| author9=Ya-Ping Zhang | journal=Molecular Ecology | year=2012 | volume=21 | issue= 4| pages=960–973 | doi=10.1111/j.1365-294X.2011.05411.x | pmid=22221323| bibcode=2012MolEc..21..960Z| s2cid=37992915}}</ref> Uplift has also driven vicariant speciation in ''[[Macowania]]'' daisies in South Africa's [[Drakensberg]] mountains,<ref>{{Citation |title=Erosive processes after tectonic uplift stimulate vicariant and adaptive speciation: evolution in an Afrotemperate-endemic paper daisy genus | author=Joanne Bentley| author2=G Anthony Verboom| author3=Nicola G Bergh | journal=BMC Evolutionary Biology | year=2014 | volume=14 | issue=27 | pages=1–16 | doi= 10.1186/1471-2148-14-27| pmid=24524661| pmc=3927823| doi-access=free| bibcode=2014BMCEE..14...27B}}</ref> along with ''[[Dendrocincla]]'' woodcreepers in the South American [[Andes]].<ref>{{Citation |title=Andean uplift promotes lowland speciation through vicariance and dispersal in Dendrocincla woodcreepers | author=Jason T. Weir | author2=Momoko Price | journal=Molecular Ecology | year=2011 | volume=20 | issue= 21| pages=4550–4563 | doi=10.1111/j.1365-294X.2011.05294.x | pmid=21981112 | bibcode=2011MolEc..20.4550W | s2cid=33626056 }}</ref> The [[Laramide orogeny]] during the [[Late Cretaceous]] even caused vicariant speciation and radiations of [[dinosaur]]s in North America.<ref>{{Citation |title=Mountain Building Triggered Late Cretaceous North American Megaherbivore Dinosaur Radiation | author=Terry A. Gates| author2=Albert Prieto-Márquez| author3=Lindsay E. Zanno | journal=PLOS ONE | year=2012 | volume=7 | issue=8 | page= e42135| doi=10.1371/journal.pone.0042135 | pmid=22876302| pmc=3410882| bibcode=2012PLoSO...742135G| doi-access=free}}</ref>

[[Adaptive radiation]], like the [[Darwin's finches|Galapagos finches]] observed by [[Charles Darwin]], is often a consequence of rapid allopatric speciation among populations. However, in the case of the finches of the Galapagos, among other island radiations such as the [[Hawaiian honeycreeper|honeycreepers]] of Hawaii represent cases of limited geographic separation and were likely driven by [[ecological speciation]].

=== Isthmus of Panama ===
[[File:Isthmus of Panama (closure) - Speciation of marine organisms (w annot).png|right|thumb|upright=1.3|A conceptual representation of species populations becoming isolated (blue and green) by the closure of the [[Isthmus of Panama]] (red circle). With the closure, North and South America became connected, allowing the exchange of species (purple). Grey arrows indicate the gradual movement of [[Plate tectonics|tectonic plates]] that resulted in the closure.]]

Geological evidence supports the final closure of the [[isthmus of Panama]] approximately 2.7 to 3.5 mya,<ref name=Hurtetal2008>{{Citation | title=A Multilocus Test of Simultaneous Divergence Across the Isthmus of Panama Using Snapping Shrimp in the Genus Alpheus|author=Carla Hurt| author2=Arthur Anker| author3= Nancy Knowlton | journal=Evolution| year=2008| volume=63| issue=2| pages=514–530| doi=10.1111/j.1558-5646.2008.00566.x|pmid=19154357|s2cid=11820649}}</ref> with some evidence suggesting an earlier transient bridge existing between 13 and 15 mya.<ref>{{Citation | title=Middle Miocene closure of the Central American Seaway|author1=C. Montes|author2= A. Cardona|author3=C. Jaramillo|author4= A. Pardo|author5=J. C. Silva|author6=V. Valencia|author7=C. Ayala|author8=L. C. Pérez-Angel|author9=L. A. Rodriguez-Parra|author10=V. Ramirez|author11=H. Niño | journal=Science| year=2015| volume=348| issue=6231| pages=226–229| doi=10.1126/science.aaa2815|pmid=25859042| display-authors=etal|bibcode=2015Sci...348..226M|doi-access=free}}</ref> Recent evidence increasingly points towards an older and more complex emergence of the Isthmus, with fossil and extant species dispersal (part of the [[Great American Interchange|American biotic interchange]]) occurring in three major pulses, to and from North and South America.<ref>{{Citation |title=Biological evidence supports an early and complex emergence of the Isthmus of Panama | author=Christine D. Bacon| author2=Daniele Silvestro| author3=Carlos Jaramillo|author4=Brian Tilston Smith|author5=Prosanta Chakrabarty|author6=Alexandre Antonelli | journal=PNAS | year=2015 | volume=112 | issue=9 | pages=6110–6115 | doi=10.1073/pnas.1423853112 | pmid=25918375| pmc=4434730| bibcode=2015PNAS..112.6110B| doi-access=free}}</ref> Further, the changes in terrestrial biotic distributions of both continents such as with ''[[Eciton]]'' army ants supports an earlier bridge or a series of bridges.<ref>{{Citation |title=Army ant invasions reveal phylogeographic processes across the Isthmus of Panama | author=Seàn Brady | journal=Molecular Ecology | year=2017 | volume=26 | issue=3 | pages=703–705 | doi=10.1111/mec.13981 | pmid=28177197 | doi-access=free | bibcode=2017MolEc..26..703B }}</ref><ref>{{Citation |title=Early and dynamic colonization of Central America drives speciation in Neotropical army ants | author=Max E. Winston| author2=Daniel J. C. Kronauer| author3=Corrie S. Moreau | journal=Molecular Ecology | year=2017 | volume=26 | issue=3 | pages=859–870 | doi=10.1111/mec.13846 | pmid=27778409| doi-access=free | bibcode=2017MolEc..26..859W}}</ref> Regardless of the exact timing of the isthmus closer, biologists can study the species on the Pacific and Caribbean sides in what has been called, "one of the greatest natural experiments in evolution".<ref name=Hurtetal2008/> Additionally, as with most geologic events, the closure was unlikely to have occurred rapidly, but instead dynamically—a gradual shallowing of sea water over millions of years.<ref name="Speciation"/>{{rp|93}}

Studies of snapping shrimp in the genus ''[[Alpheus (crustacean)|Alpheus]]'' have provided direct evidence of an allopatric speciation event,<ref>{{Citation | title=Divergence in Proteins, Mitochondrial DNA, and Reproductive Compatibility Across the Isthmus of Panama| author=Nancy Knowlton| s2cid=31875676| journal=Science| year=1993| volume=260| issue=5114| pages=1629–1632| doi=10.1126/science.8503007| pmid=8503007| bibcode=1993Sci...260.1629K}}</ref> as phylogenetic reconstructions support the relationships of 15 pairs of sister species of ''Alpheus'', each pair divided across the isthmus<ref name=Hurtetal2008/> and [[molecular clock]] dating supports their separation between 3 and 15 million years ago.<ref name=NKnowltonRoyalSoc>{{Citation | title=New dates and new rates for divergence across the Isthmus of Panama|author1=Nancy Knowlton |author2=Lee A. Weigt | journal=Proc. R. Soc. Lond. B| year=1998| volume=265|issue=1412 |  pages=2257–2263| doi=10.1098/rspb.1998.0568|pmc=1689526}}</ref> Recently diverged species live in shallow [[mangrove]] waters<ref name=NKnowltonRoyalSoc/> while older diverged species live in deeper water, correlating with a gradual closure of the isthmus.<ref name="Speciation"/>{{rp|93}} Support for an allopatric divergence also comes from laboratory experiments on the species pairs showing nearly complete reproductive isolation.<ref name="Speciation"/>{{rp|93}}

Similar patterns of relatedness and distribution across the Pacific and Atlantic sides have been found in other species pairs such as:<ref>H. A. Lessios. (1998). The first stage of speciation as seen in organisms separated by the Isthmus of Panama. In ''Endless forms: species and speciation'' (ed. D. Howard & S. Berlocher). Oxford University Press</ref>
*''[[Diadema antillarum]]'' and ''[[Diadema mexicanum]]''
*''[[Echinometra lucunter]]'' and ''[[Echinometra vanbrunti]]''
*''[[Echinometra viridis]]'' and ''E. vanbrunti''
*''[[Bathygobius soporator]]'' and ''[[Bathygobius ramosus]]''
*''B. soporator'' and ''[[Bathygobius andrei]]''
*''[[Excirolana braziliensis]]'' and variant morphs

=== Refugia ===
Ice ages have played important roles in facilitating speciation among vertebrate species.<ref name="WeirSchluter2004">{{Citation |title=Ice Sheets Promote Speciation in Boreal Birds | author=Jason T. Weir | author2=Dolph Schluter | journal=Proceedings: Biological Sciences | year=2004 | volume=271 | issue=1551 | pages=1881–1887 | doi= 10.1098/rspb.2004.2803| pmid=15347509 | pmc=1691815 }}</ref> This concept of [[Refugium (population biology)|refugia]] has been applied to numerous groups of species and their biogeographic distributions.<ref name="Speciation"/>{{rp|97}}

Glaciation and subsequent retreat caused speciation in many [[Taiga|boreal forest]] birds,<ref name="WeirSchluter2004"/> such as with North American [[sapsucker]]s ([[Yellow-bellied sapsucker|Yellow-bellied]], [[Red-naped sapsucker|Red-naped]], and [[Red-breasted sapsucker|Red-breasted]]); the warblers in the genus ''[[Setophaga]]'' (''[[Townsend's warbler|S. townsendii]]'', ''[[Hermit warbler|S. occidentalis]]'', and ''[[Black-throated green warbler|S. virens]]''), ''[[Oreothlypis]]'' (''[[Virginia's warbler|O. virginiae]]'', ''[[Oreothlypis ridgwayi|O. ridgwayi]]'', and ''[[Nashville warbler|O. ruficapilla]]''), and ''[[Oporornis]]'' (''[[MacGillivray's warbler|O. tolmiei]]'' and ''[[Mourning warbler|O. philadelphia]]'' now classified in the genus ''[[Geothlypis]]''); ''[[Fox sparrow]]s'' (sub species ''[[sooty fox sparrow|P. (i.) unalaschensis]]'', ''[[thick-billed fox sparrow|P. (i.) megarhyncha]]'', and ''[[slate-colored fox sparrow|P. (i.) schistacea]]''); ''[[Vireo]]'' (''[[Plumbeous vireo|V. plumbeus]]'', ''[[Cassin's vireo|V. cassinii]]'', and ''[[Blue-headed vireo|V. solitarius]]''); ''[[Empidonax|tyrant flycatchers]]'' (''[[Cordilleran flycatcher|E. occidentalis]]'' and ''[[Pacific-slope flycatcher|E. difficilis]]''); ''[[Poecile|chickadees]]'' (''[[Chestnut-backed chickadee|P. rufescens]]'' and ''[[Boreal chickadee|P. hudsonicus]]''); and ''[[Catharus|thrushes]]'' (''[[Bicknell's thrush|C. bicknelli]]'' and ''[[Gray-cheeked thrush|C. minimus]]'').<ref name="WeirSchluter2004" />

As a special case of allopatric speciation, [[peripatric speciation]] is often invoked for instances of isolation in glaciation refugia as small populations become isolated due to habitat fragmentation such as with North American red (''[[Picea rubens]]'') and black (''[[Picea mariana]]'') spruce<ref name="Jaramillo-Correa and Bousquet">{{Citation |title=New evidence from mitochondrial DNA of a progenitor-derivative species relationship between black and red spruce (Pinaceae) | author=Juan P. Jaramillo-Correa | author2=Jean Bousquet | journal=American Journal of Botany | year=2003 | volume=90 | issue=12 | pages=1801–1806 | doi= 10.3732/ajb.90.12.1801| pmid=21653356 }}</ref> or the prairie dogs ''[[Cynomys mexicanus]]'' and ''[[Cynomys ludovicianus|C. ludovicianus]]''.<ref name=GCM2016>{{Citation |title=Peripatric speciation of an endemic species driven by Pleistocene climate change: The case of the Mexican prairie dog (''Cynomys mexicanus'') | author=Gabriela Castellanos-Morales| author2=Niza Gámez| author3=Reyna A. Castillo-Gámez| author4=Luis E. Eguiarte| journal=Molecular Phylogenetics and Evolution  | year=2016 | volume=94 | issue=Pt A| pages=171–181 | doi=10.1016/j.ympev.2015.08.027 | pmid=26343460| bibcode=2016MolPE..94..171C}}</ref>

=== Superspecies ===
[[File:Pan (genus) distribution map.png|right|thumb|upright=1.5|The red shading indicates the range of the [[bonobo]] (''Pan paniscus''). The blue shading indicates the range of the [[Common chimpanzee]] (''Pan troglodytes''). This is an example of allopatric speciation because they are divided by a natural barrier (the [[Congo River]]) and have no habitat in common. Other ''Pan'' subspecies are shown as well.]]

Numerous species pairs or species groups show abutting distribution patterns, that is, reside in geographically distinct regions next to each other. They often share borders, many of which contain hybrid zones. Some examples of abutting species and [[Species complex|superspecies]] (an informal rank referring to a complex of closely related allopatrically distributed species, also called ''allospecies''<ref name="Amadon 1966">{{cite journal |author=Amadon D. |year=1966 |title=The superspecies concept |journal=Systematic Biology |volume=15 |issue=3 |pages=245–249 |doi=10.2307/sysbio/15.3.245}}</ref>) include:

*[[Western meadowlark|Western]], [[Chihuahuan meadowlark|Chihuahuan]], and [[Eastern meadowlark]]s in North America reside in dry western and wet eastern geographic regions with rare occurrences of hybridization, most of which results in infertile offspring.<ref name="JPrice2008"/> 
*[[Monarch flycatcher]]s endemic to the [[Solomon Islands]]; a complex of several species and [[subspecies]] ([[Bougainville monarch|Bougainville]], [[White-capped monarch|white-capped]], and [[Chestnut-bellied monarch|chestnut-bellied]] monarchs and their related subspecies).<ref name="JPrice2008"/>
*North American [[sapsucker]]s and members of the genus ''[[Setophaga]]'' (the [[hermit warbler]], [[black-throated green warbler]], and [[Townsend's warbler]]).<ref name="JPrice2008"/><ref name="WeirSchluter2004"/> 
*Sixty-six subspecies in the genus ''[[Pachycephala]]'' residing on the [[Melanesia]]n islands.<ref name="JPrice2008"/><ref>{{Citation | title=The Birds of Northern Melanesia | author=Ernst Mayr | author2=Jared Diamond | date=2001 | pages=143 | publisher=Oxford University Press | isbn=978-0-19-514170-2 }}</ref>
*[[Bonobo]]s and [[Common chimpanzee|chimpanzee]]s.
*''[[Climacteris]]'' tree creeper birds in Australia.<ref name="Mayr1963">{{Citation | title=Animal Species and Evolution | author=Ernst Mayr | date=1963 | pages=488–515 | publisher=Harvard University Press | isbn=978-0674037502 }}</ref>
*[[Bird-of-paradise|Birds-of-paradise]] in the mountains of New Guinea (genus ''[[Astrapia]]'').<ref name="Mayr1963"/>
*Red-shafted and yellow-shafted [[Northern flicker|flickers]]; [[black-headed grosbeak]]s and [[rose-breasted grosbeak]]s; [[Baltimore oriole]]s and [[Bullock's oriole]]s; and the [[Lazuli bunting|lazuli]] and [[indigo bunting]]s.<ref>Remington C.L. (1968) Suture-Zones of Hybrid Interaction Between Recently Joined Biotas. In: Dobzhansky T., Hecht M.K., Steere W.C. (eds) Evolutionary Biology. Springer, Boston, MA</ref> All of these species pairs connect at zones of hybridization that correspond with major geographic barriers.<ref name="Speciation"/>{{rp|97–99}}
*''[[Dugesia]]'' flatworms in Europe, Asia, and the Mediterranean regions.<ref name="Mayr1963"/>
*Dichromatic toucanets of the genus ''[[Selenidera]]'' may be a superspecies that arose by the refugia hypothesis in the [[Amazon basin]].<ref>{{Citation|title=Speciation in Amazonian Forest Birds |author=Jürgen Haffer |journal=Science |year=1969 |volume=165 |issue= 3889|pages=131–137 |doi= 10.1126/science.165.3889.131|pmid=17834730 |bibcode=1969Sci...165..131H }}</ref>

In birds, some areas are prone to high rates of superspecies formation such as the 105 superspecies in [[Melanesia]], comprising 66 percent of all bird species in the region.<ref>{{Citation | title=The Birds of Northern Melanesia | author=Ernst Mayr | author2=Jared Diamond | date=2001 | pages=127 | publisher=Oxford University Press | isbn=978-0-19-514170-2 }}</ref> [[Patagonia]] is home to 17 superspecies of forest birds,<ref>{{Citation |title=Forest Birds of Patagonia: Ecological Geography, Speciation, Endemism, and Faunal History | author=François Vuilleumier | journal=Ornithological Monographs | year=1985 | issue=36 | pages=255–304 | doi=10.2307/40168287 | jstor=40168287 }}</ref> while North America has 127 superspecies of both land and freshwater birds.<ref>Mayr, E., & Short, L. L. (1970). ''Species taxa of North American birds: a contribution to comparative systematics''.</ref> [[Sub-Saharan Africa]] has 486 [[passerine]] birds grouped into 169 superspecies.<ref>Hall, B. P., & Moreau, R. E. (1970). ''An atlas of speciation in African passerine birds''. Trustees of the British museum (Natural history).</ref> Australia has numerous bird superspecies as well, with 34 percent of all bird species grouped into superspecies.<ref name="JPrice2008"/>