Wallace's Line in the Light of Recent Zoogeographic Studies Author(s): Ernst Mayr Source: The Quarterly Review of Biology, Vol. 19, No. 1 (Mar., 1944), pp. 1-14 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/2808563 . Accessed: 03/02/2015 17:45 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to The Quarterly Review of Biology. http://www.jstor.org This content downloaded from 134.173.140.68 on Tue, 3 Feb 2015 17:45:35 PM All use subject to JSTOR Terms and Conditions VOL. 19, NO. I March,I 944 THE QUARTERLY REVIEW of BIOLOGY WALLACE'S LINE IN THE LIGHT OF RECENT ZOOGEOGRAPHIC STUDIES BY ERNST MAYR AmericanMuseum of Natural History, New York Z OOGEOGRAPHY has had a fate very by the Atlantic,do not differso widelyas Asia muchlike taxonomy. It was flourishing and Australia." There is much truth,in this duringthe descriptive period of biological statement. Except for bats and a few rodents, sciences. Its prestige,however, declined the onlynative mammalsof Australiaare marsu- rapidlywhen experimental biology began pials and monotremes. These same two groups to come to the foreground.Again as with taxon- are entirelylacking in Asia and are replacedby a omy, a new interestin zoogeographyhas been wide varietyof placentalmammals, such as mon- noticeablein recentyears. It seems to me that keys, shrews,squirrels, ungulates, and so forth. this revival has had two causes. One is the An equally pronouncedfaunal differenceexists interestof the student of geographicspeciation among birds,insects, and othergroups of animals in the findingsof the zoogeographer. A studyof of the two regions. past and present distributionsyields much in- Australiaand Asia are connectedby a belt of formationon isolationof populationsand on the islands,the Malay Archipelago,and the question dispersalof species. It-is in this connectionthat naturallycomes up as to where in this island I became interestedin zoogeography. regionthe borderlineis to be drawnbetween these The other reason is the introductionof new two fundamentallydifferent faunas. After re- methods. The intensiveexploration of all corners viewing the zoological evidence known to him, of the globe duringthe past fiftyyears has led Wallace (l.c.) comes to the followingconclusion: to an accumulationo; sufficientfaunistic data "We may considerit establishedthat the Strait to permitthe applicationof statisticalmethods. of Lombok [betweenBali and Lombok] (only 15 Furthermore,the science of ecology has reached mileswide) marksthe limit and abruptlyseparates a levelof maturityat whichit is beginningto affect two of the great zoologicalregions of the globe." profoundlyzoogeographic methods and principles. With thesewords he drewa zoogeographicbound- It seemedworth while to me to studythe contro- ary which was destinedto gain fame under the versialand stillwide open subjectof theborderline name of its author: "Wallace's Line," a termfirst between the Australian and Oriental Regions used by Huxley (1868) (Fig.' 1). It runsbetween withthe help of such modernmethods. Bali and Lombok in the south, then through A. R. Wallace, who is generallyconsidered the Makassar Strait between Borneo and Celebes, foremostrepresentative of classicalzoogeography, and finallyturns into the open Pacific between states in his famousessay On thezoological geog- Mindanao (Philippines)and the SanghirIslands. raphy of the Malay Archipelago(1860): "The This convenientborderline found quick acceptance westernand eastern islands of the archipelago in the zoological literature and was without belong to regions more distinctand contrasted hesitation adopted by nearly all 'the zoogeog- than any other of the great zoological divisions raphers publishing between 1860 and 1890. ofthe globe. SouthAmerica and Africa,separated Sarasin (1901) and Pelseneer (1904) should be 1 This content downloaded from 134.173.140.68 on Tue, 3 Feb 2015 17:45:35 PM All use subject to JSTOR Terms and Conditions 2 THE QUARTERLY REVIEW OF BIOLOGY consultedfor a historicalsurvey of the earlier facts became better known. Wallace himself literature.The echoin thepopular literature of was muchless positivein his laterwritings. Since this period was even more enthusiastic.A then many writershave insistedthat 'Wallace's mysteriousljne, only 15 mileswide, that separates Line was entirely imaginary (Weber (1902), marsupialsfrom tigers, and honeyeaters and Pelseneer (1904), Mertens (1930), Brongersma cockatoesfrom barbets and trogons,could not (1936), and others). Van Kampen (1909), for failto appeal to theimagination of thelayman. example, asserted: "Such a sharp boundary as -- Waltacestime ofi(uxle4) V~ 1.I ~~~~~~~~~~~~~~~~~ 1_7jj-- - Wallace'Ltne rinal) n F z Webeef t >m (Faunl Balanlc) ''-'-' tf | ~~/L fAtoPapuanb ainlandFauna ' - BDORNEO ______s -- - Ula_lacesItne -O- +i*a L .0.0/ .. I Ulbe' Ltne(Fana hBalance 9 / as du I W~~~Uallace'slie (of ifuxleql) /_____ l--UIallaceslne (Original) /'.= Uleber~sI ne (Faunal B3alance) __ - - Ilieber'sJlJe (of Pelseneer) 1_ A +- +- LpitofA8ustralo-PapuanMainlandFauna .j_STRALI ZOO-mIme (Nd,e of Continental Thelves) .2 iUST 2 LIA* le'dta4Qy_deI. ||* J_t, FIG 1. ZOOGEOGRAPHIc BORDERLINES IN THE MALAY ARCHIPELAGO The shaded areas are the continentalshelves. E. Haeckel (1893) outdid all his contemporaries Wallace drewit does not exist. Not onlyis there by asserting:"Crossing the narrow but deep none where he drew it, but no such line exists Lombok Strait we' go with a single step from anywhere in the archipelago." On the other the PresentEra to the Mesozoicum." hand,Wallace's Line has been vigorouslydefended Statementsof such exaggerationcall forrefuta- by such serious,authorsas Dickersonet al. (1928), tion and shortlyafter 1890 doubtswere expressed Raven (1935), and Rensch (1936). Curiously more and more frequentlyas to the validity of enoughmost of the writerson this subject seem Wallace's Line,particularly after the distributional to be definitelyin one or the othercamp, either This content downloaded from 134.173.140.68 on Tue, 3 Feb 2015 17:45:35 PM All use subject to JSTOR Terms and Conditions WALLACE'0S LINE 3 theyare forWallace's Line or theyare againstit, island belt,frofii,fhe east as a descendantof a and they tend to presenttheir data accordingly. group of species that was isolated in Australia Others treat one aspect only of this diversified at an early date. Such secondarilyeastern ele- problem. An impartialstudy of the situationis ments,as Merops ornatusamong the birds, are stilllacking at the presenttime. includedwith the easterngroup. The classifica- Actually, a whole complex of questions is tion of a few species will always remainopen to involved,of which the followingseem to be the doubt, but a differentdecision in these cases most importantones: would change the percentagesonly slightlyand (1) Is Wallace's Line the borderlinebetween would not basically affectthe followingfigures. the Orientaland the AustralianRegions, and if A specialistof a given group usually has no dif- not, whereis thisborderline? ficulties in deciding which species are Indo- (2) Does Wallace's Line representthe line of a Malayan and whichAustralian. major faunal break, and if this is true,how did Celebes. Weber (1902), the Sarasins (1901), such a break develop? de Beaufort(1926), Stresemann(1939) and other recentauthors agree that at least threefourths of IS WALLACE' S LINE THE BOUNDARY BETWEEN THE the Celebes animals are of westernorigin. Ac- ORIENTAL AND THE AUSTRALIAN REGIONS? cording to Rensch (1936: 252) the figuresare: The faunaof the Malay Archipelagowas rather Reptilesat least 88 per cent,Amphibia 80 per cent poorlyknown in Wallace's days. Wherehe knew TABLE 1 20 species of birds,we now know 120; wherehe Percentageof westernand eastern species on Lesser Sunda knew 5 species of reptiles,we know 40, and so Islands forth. This lack of informationcaused Wallace to singleout what he consideredtypical represen- REPTILES AND AM- BIRDS CHANGE tatives of the respectivefaunas, and to use the PHIBIANS OF PER- CENTAGE borderline of their ranges as zoogeographic IN BIRDS Western WesternEastern boundaries. The tiger,the squirrelsand other mammalsgo as far east as Bali, but are absent Per cent Per centPer cent fromLombok. Among birds the barbets (Capi- Bali.............. 94 87.0 13.0 14.5 tonidae) and many other Oriental groups are Lombok........... 85 72.5 27.5 4.5 abruptlybrought to a halt by Lpmbok Strait. Sumbawa.. 87 68.0 32.0 5.0 Flores.78 37.0 The Australianhoneyeaters (genera Philemon and 63.0 5.5 AlorGroup . - 57.5 42.5 Meliphaga) and the cockatoe (Cacatua) reach Lombok, but not Bali.' The faunal difference on eitherside of Makassar Strait is even more and butterflies86 per cent. In birdsthe figureis striking:A rich Orientalfauna on Borneo and a slightlylower. Among 74 species of Passerine marsupia'l(Phalanger) on Celebes. It was on the birds 67.6 per cent are western. The percentage basis of such data that Wallace came to the con- for the old endemics (genera and