Biogeographical RegionsRichard Huggett, The University of Manchester, Manchester, UK

Species are not uniformly distributed over the globe. The

largest regions of animal and plant assemblages are bio-

geographical regions, each bearing a distinctive fauna

and flora. Some families and even some orders of animals

are endemic to particular biogeographical regions; other

families are shared by two or more regions; a few families

arecosmopolitanand found in all regions.The delineation

of traditional biogeographical regions was rather sub-

jective. Recently, increased availability of global species

range maps, the development of new multivariate tech-

niques and improved computational power have led to

quantitative regionalisations that are broadly similar to

traditional regions but do show differences. The transi-

tion zones between are sometimes gradual, as in the

junction between the Oriental and Australian faunal

regions. The state of biogeographical regions is under

threat from such human activities as habitat destruction

and fragmentation and the introduction of alien species,

and it will decline without conservation measures.

Sclater PL, Wallace AR and theFoundational Units of Biogeography

Different places harbour different kinds of animals andplants. The fauna of Africa is unlike the fauna of NorthAmerica; the flora of Japan is unlike the flora of SouthAfrica. These regional differences in the distribution ofspecies became increasingly manifest as the world wasexplored. George Leclerc, Compte de Buffon (1707–1788)studied the then known tropical mammals from the OldWorld (Africa) and the New World (Central and South

America). He found that they had not a single species incommon, a finding that gave rise to Buffon’s law, theobservation that regions of similar climate in different partsof the world house different sets of species. Later com-parisons of African and South American plants, insectsand reptiles evinced the same pattern. See also: Buffon,Georges LouisBy the nineteenth century, it was clear that the land

surface is divisible into biogeographical regions, each ofwhich carries a distinct set of animals and a distinct set ofplants, a pattern called biogeographical provincialism.Augustin-Pyramus de Candolle considered plants andidentified areas of endemism, that is botanical regions, eachpossessing a certain number of plants peculiar to them. Helisted 20 such botanical regions or areas of endemism in1820, and by 1838 had added another score, bringing thetotal to 40. In 1826, James Cowles Prichard, a zoologist,distinguished seven regions ofmammals: theArctic region,the temperate zone, the equatorial regions, the Indian isles,the Papuan region, the Australian region and the extrem-ities of America and Africa. William Swainson modifiedthis scheme in 1835, by taking account of the ‘five recordedvarieties of humans’, to give five regions: the European (orCaucasian) region, the Asiatic (or Mongolian) region, theAmerican region, theEthiopian (orAfrican) region and theAustralian (or Malay) region. See also: de Candolle,Augustin-Pyramus; Prichard, James CowlesThe seminal work of an English ornithologist, Philip

Lutley Sclater, and the eminent English biogeographerand naturalist, Alfred Russel Wallace, eclipsed the earlyideas of Prichard and Swainson on animal distributions.Using bird distributions, Sclater (1858) recognised twobasic divisions (or ‘creations’, as he termed them) – the OldWorld (Creatio Paleogeana) and the New World (CreatioNeogeana) – and six regions. The Old World he dividedintoEurope and northernAsia, Africa south of the Sahara,India and southern Asia and Australia and New Guinea.The NewWorld he divided into North America and SouthAmerica. Sclater’s schema prompted a flurry of papers byEnglish-speaking zoologists, including Thomas HenryHuxley and Joel Asaph Allen, each of whom promulgatedhis own favoured geographical classification. In his The

Introductory article

Article Contents

. Sclater PL, Wallace AR and the Foundational Units of

Biogeography

. Mammals

. Floral Regions

. Comparisons and Contrasts between Taxa

. Transitional Zones and Filters

. The Applied Use of Biogeographical Regions: Their

Place in Conservation

. Summary

Online posting date: 17th October 2011

eLS subject area: Ecology

How to cite:Huggett, Richard (October 2011) Biogeographical Regions. In: eLS.John Wiley & Sons, Ltd: Chichester.

DOI: 10.1002/9780470015902.a0003231.pub2

eLS & 2011, John Wiley & Sons, Ltd. www.els.net 1

Geographical Distribution of Animals (Wallace, 1876),Wallace reviewed the competing systems, arguing per-suasively in favour of adopting Sclater’s six regions, orrealms as Wallace dubbed them. Sclater’s system andWallace’s minor amendments to it provided a nomen-clature that survives today (Figure 1). Later suggestionswere minor variations on the Sclater–Wallace theme.Sclater and Wallace identified six regions – Nearctic,Neotropical, Palaearctic, Ethiopian, Oriental and Aus-tralian. Together, the Nearctic and Palaearctic regionsform Neogaea (the New World), whereas other regionsform Palaeogaea (the Old World). Wallace’s contributionwas to identify subregions, four per region, which corres-pond largely to de Candolle’s botanical regions. Indeed,the nineteenth-century classification of biogeographicalregions was essentially an attempt to group areas ofendemism into a hierarchical classification according to thestrengths of their relationships. Note that Cox (2001), in astudy of biogeographical regions, considered the namesNeotropical, Nearctic and Palaearctic to be cumbersomeand unnecessary, favouring South American, NorthAmerican and Eurasian as plain alternatives. See also:Huxley, Thomas Henry; Wallace, Alfred Russel

It is surprising and noteworthy that the distributionsof species with good dispersal abilities, including plants,insects and birds, tend to fall within traditional zoo-geographical regional confines. The avifaunas of NorthAmerica and Europe contain several families and manygenera that are not shared by the two regions, even thoughdispersal across the North Atlantic and Pacific Oceans by‘accidental visitors’ is noted every year. Even long-distancemigrant bird taxa tend to be confined either to the easternhemisphere or to the western hemisphere, where theymigrate between high and low latitudes, and appear ill dis-posed to disperse east–west between continents (Bohning-Gaese et al., 1998).

Biogeographical regions are not purely of academicinterest. They capture basic patterns in the geographicalorganisation of life on Earth created by past and currentphysical and evolutionary forces. They therefore providea spatial framework for many pure and applied questionsin historical and ecological biogeography, evolutionarybiology, systematics and conservation (Morrone, 2009;Kreft and Jetz, 2010).

Mammals

Of the six faunal regions delineated by Sclater andWallace,the Palaearctic is the largest. It includes Europe, NorthAfrica, theNear East andmuch of Asia (but not the Indiansubcontinent or SoutheastAsia). Itsmammal fauna is quiterich, with some 40 families. Only two of these families areendemic to the Palaearctic region – the blind mole rats(Spalacidae) and the Seleviniidae, represented by one spe-cies, the dzhalman, which is a small insectivorous rodent.See also: MammaliaThe Nearctic region encompasses nearly all the New

World north of tropical Mexico. Its fauna is diverse andincludes families with a largely tropical distribution, suchas the sac-winged or sheath-tailed bats (Emballonuridae),vampire bats (Desmodontidae), and javelinas or peccaries(Tayassuidae) and largely boreal families, such as thejumping mice (Zapodidae), beavers (Castoridae), andbears (Ursidae). Only twoNearctic families are endemic tothe region: the Aplodontidae, which contains one species,the mountain beaver or sewellel, and the Antilocapridae,which also contains one species, the pronghorn antelope.Two other families are almost endemic: the pocket gophers(Geomyidae) live in North America, Central America andnorthern Colombia; and the kangaroo rats and pocketmice (Heteromyidae) live in North America, Mexico,Central America and northwestern South America.TheNeotropical region covers all theNewWorld south of

tropical Mexico. It boasts some 27 endemic families ofmammals: the solenodons (Solenodontidae), the recentlyextinct West Indian shrews (Nesophontidae), New Worldmonkeys (Cebidae), marmosets (Callithricidae), caeonoles-tidsormarsupialmice (Caenolestidae), themonitodelmonteor ‘monkeyof themountains’ (Microbiotheriidae), anteaters(Myrmecophagidae), sloths (Bradypodidae) and 12 cavio-morph rodent families. The rodent families are the degus,coruros and rock rats (Octodontidae), tuco-tucos (Cteno-myidae), spiny rats (Echimyidae), rat chinchillas (Abroco-midae), hutias and coypus (Capromyidae), chinchillas andviscachas (Chinchillidae), agouties (Dasyproctidae), pacas(Cuniculidae), the pacarana (Dinomyidae), guinea-pigs andtheir relatives (Caviidae), capybaras (Hydrochoeridae) andthe recently extinct quemi and its allies (Heptaxodontidae).The other seven endemic Neotropical families are bats –bulldog bats (Noctilionidae), New World leaf-nosed bats(Phyllostomidae), moustached bats, ghost-faced bats andnaked-backed bats (Mormoopidae), vampire bats (Des-mondontidae, which some authorities include with the

Nearctic Neotropical Palaearctic

Ethiopian Oriental Australian

Figure 1 The six faunal regions delimited by Sclater and Wallace.

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Phyllostomidae), funnel-eared bats (Natalidae), smoky orthumbless bats (Furipteridae) and disc-winged bats (Thyr-opteridae). See also: Xenarthra and Pholidota (Armadillos,Anteaters, Sloths and Pangolins); NewWorld Monkeys

The Ethiopian region encompasses Madagascar, Africasouth of a somewhat indeterminate line running across theSahara, and a southern strip of theArabianpeninsula. It hasabout 15 endemic families, almost as many as the Neo-tropical region. The families are the giraffes (Giraffidae),hippopotamuses (Hippopotamidae, though those living onthe LowerNile are technically in the Palaearctic region), theaardvark (Orycteropodidae), tenrecs (Tenrecidae), the OldWorld sucker-footed bats (Myzopodidae), lemurs (Lemur-idae), woolly lemurs (Indriidae), aye-ayes (Daubentonii-dae), two families of shrew and five families of rodent. Theshrew families are the golden moles (Chrysochloridae) andotter shrews (Potamogalidae). The rodent families are thescaly tailed squirrels (Anomaluridae), the spring hare orCape jumpinghare (Pedetidae), cane rats (Thryonomydiae),the rock rat or dassie rat (Petromyidae) and African molerats (Bathyergidae). Two other families – the elephantshrews (Macroscelididae) and gundis (Ctenodactylidae) –are confined to Africa but range into the north of the con-tinent, which is part of the Palaearctic region.

The Oriental region covers India, Indo-China, southernChina,Malaysia, the Philippines and Indonesian islands asfar east as Wallace’s line. It has just four endemic families:spiny dormice (Platacanthomyidae), tree shrews (Tupaii-dae), tarsiers (Tarsiidae) and flying lemurs or colugos(Cynocephalidae). It also has one endemic bat family, theCraseonycteridae, represented by a single species known asKitti’s hog-nosed bat or bumblebee bat, which was dis-covered in Thailand in 1973.

The Australian region includes mainland Australia, Tas-mania, New Guinea, Sulawesi and many small Indonesianislands. It possesses some 19 endemic families of mammals:the echidnas or spiny anteaters (Tachyglossidae), theplatypus (Ornithorhynchidae), marsupial ‘mice’ and ‘cats’(Dasyuridae), the Tasmanian wolf (Thylacinidae),the numbat or banded anteater (Myrmecobiidae), the mar-supial mole (Notoryctidae), bandicoots and bilbies (Per-amelidae), burrowing bandicoots (Thylacomyidae), spinybandicoot and mouse bandicoot (Peroryctidae), stripedpossum, Leadbeater’s possum and wrist-winged gliders(Petauridae), feathertail gliders (Acrobatidae), pigmy pos-sums (Burramyidae), brush-tailed possums, cuscuses, scalytailed possums (Phalangeridae), ringtail possums and greatglider (Pseudocheiridae), kangaroos and wallabies (Macro-podidae), rat kangaroos, potoroos and bettongs (Potor-oidae), koalas (Phascolarctidae), wombats (Vombatidae)and the noolbender or honey possum (Tarsipedidae).See also: Marsupialia (Marsupials); Monotremata

Floral Regions

In The Geography of the Flowering Plants (Good, 1974),British botanist RonaldGood summarised the distribution

of living angiosperms by adapting a scheme devised byAdolf Engler during the 1870s. Good delineated six majorfloral regions, though he styled them ‘kingdoms’: theBoreal region, the Palaeotropical region, the Neotropicalregion, the Australian region, South African (Cape) regionand the Antarctic floral region. Each of these comprises anumberof subregions (Goodcalled themregions), ofwhichthere are 37 in total (Figure 2). A similar set of floral ‘king-doms’ based on levels of endemism was delineated byTakhtajan (1986). The Boreal floral region spans NorthAmerica and Eurasia, which share many families, includ-ing the birches, alders, hazels and hornbeams (Betulaceae),mustard (Cruciferae), primrose (Primulaceae) and butter-cup (Ranunculaceae). Six subregions are recognised: theArctic and Subarctic, EastAsia,Western andCentral Asia,the Mediterranean, Euro-Siberia and North America. ThePalaeotropical region covers most of Africa, the Arabian

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Neotropical region24

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Figure 2 The six floral regions and 37 subregions mapped by Good.

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peninsula, India, southeast Asia and parts of the westernand central Pacific. The subregions are not firmly agreed,but Malesia, Indo-Africa and Polynesia are commonlyrecognised. The Malesian subregion is exceptionally richin forms, with about 400 endemic genera. Madagascar,which is part of the Indo-African subregion but sometimestaken as a separate region, has 12 endemic families and350 endemic genera. The Neotropical region covers mostof South America, save the southern tip and a south-western strip, Central America, Mexico (excepting the drynorthern and central sections) and the West Indies andsouthern extremity of Florida. It is gloriously rich flor-istically, housing 47 endemic families and nearly 3000endemic genera. The Cape region of South Africa is, for itssmall size, rich in plants, with 11 endemic families and 500endemic genera. The Australian region is highly distinctwith 19 endemic families, 500 endemic genera and over6000 flowering-plant species. The Antarctic region has acurious geography and includes a coastal strip of Chile andthe southern tip of South America, the Antarctic andsubantarctic islands and New Zealand. The subantarcticsubregion (southern Chile, Patagonia and New Zealand)carries a distinctive flora involving some 50 genera, ofwhich the southern beech (Nothofagus) is a characteristicelement. See also: Angiosperms

Comparisons and Contrasts betweenTaxa

The world’s regional faunas are linked with each other incomplex ways, as are the world’s regional floras. Con-nections at the species level are weak, except between thePalaearctic and Nearctic regions, but some regions sharegenera and families. Eachbiogeographical regionpossessestwo groups of families: those that are endemic or peculiarto the region, and those that are shared with other regions.Although no agreed systemof naming shared taxa (species,genera, families or whatever) exists, a useful scheme sug-gests that taxa shared between twobiogeographical regionsare ‘characteristic’, taxa shared between three or fourbiogeographical regions are ‘semicosmopolitan’, and taxashared between five or more biogeographical regions are‘cosmopolitan’. Links between regions are suggested by amixing of some faunal or floral elements. AMalesian floralelement is present in the tropical rainforests of northeasternQueensland, Australia. Antarctic and Palaeotropical florainterdigitate in South Island of New Zealand, Tasmaniaand the Australian Alps. The strong affinity of the Ethi-opian and Oriental faunal regions is reflected in a numberof shared families: bamboo rats (Rhizomyidae), elephants(Elephantidae), rhinoceroses (Rhinocerotidae), chevro-tains (Tragulidae), lorises and pottos (Lorisidae), galagosor bushbabies (Galagonidae), apes (Pongidae) and pan-golins or scaly anteaters (Manidae). See also: Apes;Perissodactyla (Odd-Toed Ungulates Including Horses,

Rhinoceroses and Tapirs); Primates (Lemurs, Lorises,Tarsiers, Monkeys and Apes); Proboscidea (Elephants)

A new look at mammal regions

When Sclater and Wallace were delineating their bio-geographical regions, knowledge of species distributionsand phylogenetic relationships was restricted. They usedintuition tempered with extensive taxonomic and faunisticexpertise (educated guesswork) to set boundaries. In con-sequence, their exact criteria for recognising and delineat-ing biogeographical units were rather ill-defined. Becauseof this, their traditional regions rest upon qualitative evi-dence and lack precision, which limit their utility. In recentyears, three developments have aided fresh and more pre-cise quantitative studies of biogeographical regionalisa-tions: the increased availability of global species rangemaps; the development of new multivariate techniques;and hugely improved computational power.An early example of such work is Smith’s (1983a, b)

efforts to apply multidimensional scaling to data on thedistribution of 115 mammal families (wholly marinefamilies and the human family were omitted) in Wallace’s24 subregions. The result was the delineation similarregions to those in the Sclater–Wallace scheme, but withsignificant differences emerged. In Smith’s (1983a, b) sys-tem, there are four regions – Holarctic, Latin American,Afro-Tethyan and Island – and 10 subregions (Figure 3).The Holarctic region comprises the Nearctic and thePalaearctic subregions; the Latin American region com-prises theNeotropical andArgentine subregions; theAfro-Tethyan region comprises the Mediterranean, Ethiopianand Oriental subregions; and the Island region comprisesthe Australian, the West Indian and Madagascan sub-regions. Each subregion is as unique as it can be comparedwith all other subregions. Several features of Smith’ssystem are intriguing. First, it reveals a close similitudebetween the mammal families of the Ethiopian andOriental regions. Second, it includes the Mediterranean

Holarctic LatinAmerican

Afro-Tethyan Island

Near ctic

WestIndian

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AustralianMadagascan

Figure 3 The four faunal regions and 10 subregions recognised by Smith.

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subregion within the Ethiopian region, thus excluding itfrom the Palaearctic region. Third, it promotes Mada-gascar and the West Indies to distinct island subregions,removing them from the Ethiopian region and the Neo-tropical region, respectively.

The regional richness and endemicity of mammalfamilies in Smith’s regions and subregions are as follows:the Holarctic has 36 families, of which six (17%) areendemic; the Latin American region has 48 families, ofwhich 20 (42%) are endemic; the Afro-Tethyan region has65 families, of which 29 (45%) are endemic; and the Islandregion has 35 families, of which 15 (43%) are endemic.Of the 115 mammal families used in the analysis, 43 (37%)are endemic to subregions. The lowest subregionalendemicity occurs in the Palaearctic subregion, with noendemic families, and the highest in the Neotropical sub-region, with nine endemic families. Smith’s analysis alsoindicated that the Nearctic, Palaearctic, MediterraneanandOriental subregions have high affinities with the faunasof other subregions, whereas the Argentine and Australiansubregions have low affinities with the faunas of othersubregions. Furthermore, the effects of isolation orinaccessibility (or both) are reflected in the nature of theNeotropical, Argentine, Ethiopian, Australian, WestIndian and Madagascan faunas.

Far more recently, Kreft and Jetz (2010) have developeda methodological roadmap for species-level bio-geographical regionalisations at the global scale usingnonmetric multidimensional scaling (they used nine dif-ferent clustering techniques) and have applied it to mam-mals. Figure 4 shows the dendrogram and map resultingfrom their unweighted pair-groupmethod using arithmeticaverages (UPGMA) agglomerative hierarchical clusteringof grid-cell assemblages of mammals, which method per-sistently performed the best of the nine tested. The largecoloured rectangles show the six major biogeographicaldivisions, which are highlighted in the dendrogram withlarge coloured rectangles: orange, Australian; red, Neo-tropical; brown, African; yellow, Oriental; blue, Palae-arctic; green, Nearctic. The first thirty groups in thedendrogram (small rectangles) and in the map are dis-played in different colours; and the first sixty groups areindicated with black boundaries in the map. These newbiogeographical regions delineated on a quantitative basisshowmarked similarities to and differences from the classiczoogeographical regions. An important difference is theindication that the Sahara, northern Africa, the ArabianPeninsula and parts of the Middle East belong in terms ofbiogeography to the African tropics.

In broad terms, the major geographical divisions in theglobal mammal fauna coincide with tectonic plate bound-aries. For instance, the southern boundary of the Nearcticregion marks the southern edge of the North Americanplate;whereas theNeotropical regions sits on theCaribbeanand South American plates. The India and Sri Lanka sub-region coincides with the Indian plate. Many islands andarchipelagos as isolated landmasses also support distinctbiogeographical subregions; an example isMadagascar. At

a finer geographical scale, regional biogeographical div-isions increasingly mirror broad zones of climate andvegetation, witness the Guineo-Congolian subregion cor-responding to the African tropical rain forest zone and theCentral Asian steppe subregion corresponding to theEurasian temperate grassland zone (Figure 4).

Faunal and floral regions compared

The major floral regions and the major faunal regions areroughly congruent, but there are important differencesbetween them. First, owing to the superior dispersal abilityof some plants compared with terrestrial mammals, thefloral regions tend to be less sharply defined than do thefaunal regions. Second, although the boreal floral region isequivalent to the combinedPalaearctic andNearctic faunalregions (the Holarctic region), the North American floralsubregion differs from the Nearctic faunal region in that itdoes not occupy all of Florida or Baja California. ThePalaeotropical floral region is equivalent to the combinedEthiopian and Oriental faunal regions or a large part ofSmith’s Afro-Tethyan region, excluding the Mediterra-nean, which is floristically grouped with the Boreal region.The Australian floral region approximately correspondswith the Australian faunal region, though the dividing linewith the Asian region lies between Australia and NewGuinea, rather than farther west as in the case of animals.Indeed, it is puzzling that the flora of New Guinea isPalaeotropical whereas its fauna is Australian. The Neo-tropical floral region broadly matches the Neotropicalfaunal region, but the floral Neotropical region, unlike thefaunalNeotropical region, takes in Baja California and thesouthern end of Florida. The Cape floral region, whichoccupies the southern tip of Africa, bears no equivalentfaunal region. The Antarctic floral region, which, like theCape floral region, possesses no faunal counterpart,includes southern South America and New Zealand, andsome of its members are found in Tasmania and south-eastern Australia.

Transitional Zones and Filters

The chief faunal and floral regions are separated from oneanother by various kinds of barriers determined mainly byclimate, mountains and water gaps. The Nearctic is sep-arated from the Palaearctic by two water gaps – the BeringStrait and the Norwegian Sea, both of which experiencecold climates. A narrow land-link (the Isthmus of Pan-ama), which replaced an earlier water gap, separates theNearctic region from the Neotropical region, with aridconditions lying north of the land link in Mexico. TheSahara Desert divides the Palaearctic region from theEthiopian region. The Ethiopian region is insulated fromthe Oriental region by arid lands in southwest Asia and theArabian peninsula. The Himalayas and their eastwardextensions create a formidable barrier between theOrientalregion and the Palaearctic region. In the region sometimes

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1.0 0.8

Dissimilarity (�sim)

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Tasmania (5)Southern & Central Australia (521)Northern Australia (93)New Guinea (67)New Caledonia (1)Madagascar (49)Patagonia (147)Central Andes (114)Tropical Southern & Central America (1235)Antilles (14)Guineo-Congolian (250)Southern Africa (226)African Savannas and Woodlands (979)Sahara (876)Northern Africa (45)Arabo-Sindic (452)Turkic-Armenian (100)Sulawesi (12)Sundaland (128)Phillippines (17)India & Sri Lanka (273)Indo-China (383)Korean-Manchurian (151)Japan (33)Tibetan plateau (228)Central Asian steppe (446)Temperate and Boreal Euro-Siberia (2065)Southern North America (245)Temperate North America (561)Boreal & Arctic Zone of North America (973)

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Figure 4 Dendrograms and maps resulting from UPGMA hierarchical clustering of grid cell assemblages of mammals. On the map, boundary widths are

proportional to the height in the UPGMA dendrogram where adjacent groups merge. Modified Behrmann projection. Source: Adapted from Kreft and Jetz

(2010).

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called Wallacea, a series of water gaps hinders movementbetween the Oriental region and the Australian region.

The borders between biogeographical regions may becrossed with varying levels of ease or difficulty. Seldom dothe environmental conditions in the border areas allowunhampered access between regions. A fairly open borderonce existed between Alaska and Siberia when, during thePleistocene epoch, there was a dry-land connection acrosswhat is now the Bering Strait. Other borders tend to act asfilters and prevent the passage of some species from onebiogeographical region to another. In many cases, theborder area is transitional as the fauna or flora of onebiogeographical region intermixes with the fauna or floraof an adjacent biogeographical region. Two cases willillustrate these points.

Wallacea

Wallacea is the famous zoogeographical transition zonebetween Lydekker’s line andWallace’s line (Figure 5). It is alarge area in which Oriental and the Australian faunasgrade into one another (see Vane-Wright, 1991; Michaux,1994). The faunas of both these regions thin out across thetransition zone. Wallace’s line, which passes between Baliand Lombok and along the Makassar Strait betweenBorneo andSulawesi,marks the easternmost extensionof awholly Oriental fauna. A few Oriental species (shrews,civets, pigs, deer and monkeys) have colonised Sulawesiand Bali, but they are genetically distinct from their rela-tives in the Oriental region. A very few Oriental species, allof which might have been introduced, occur on the islandsas far east as Timor, but no Oriental species live beyondthat point. Lydekker’s line, which passes between theAustralian mainland and Timor and between NewGuineaand Seram and Halmahera, follows the edge of Australia’scontinental shelf (the Sahul Shelf). It marks the western-most limit of a wholly Australian fauna. A few Australianspecies are found on some small islands a little to the west,

and as far west as Sulawesi and Lombok. Weber’s line(Figure 5) runs west of theMoluccas and east of Timor, andmarks places with an equal mix of Oriental and Australianspecies. Some authorities take it as the dividing linebetween the Oriental and Australian faunas. Kreft andJetz’s (2010) study suggests that the position of the NewGuinean continental shelf – Lydekker’s Line – is anappropriate border to separate theOriental andAustralianregions (Figure 4).

The Isthmus of Panama

South America presently connects with North America,but for most of the last 65 million years or so it was anisland-continent. Once during that time, from about 40 to36 million years ago (Ma), a land connection with NorthAmerica, probably through a chain of islands, may haveexisted which two groups of mammal – primates andancestors of the caviomorph rodents – took advantage ofand invaded South America. However, the latest researchsuggests that these groups came from Africa (Flynn et al.,2007). Having arrived in South America, both groupsunderwent an impressive adaptive radiation to produce thegreat variety of rodents andNewWorld monkeys found inSouth America today. From 30 to 6Ma, South Americaremained a colossal island andmammals had no possibilityof interactionwith other faunal regions. Even as recently as6Ma, the Bolivar Trough connected the CaribbeanSea with the Pacific Ocean and deterred the passage ofanimals. However, at that time, members of two familiesof mammals – the ‘field mice’ (Cricetidae) and racoons,cacomistles, coati-mundis, kinkajous and olingos (Pro-cyonidae) – rafted across the seaway on clumps of soil andvegetation. By 3Ma, a land connection – the Panamanianland bridge – had developed that supplied a gateway forfaunal interchange between North and South America.A flood of mammals simply walked into South America.Members of many families were involved: Cervidae(deer), camels (Camelidae), peccaries (Tayassuidae), tapirs(Tapiridae), horses (Equidae), mastodons (Gomphother-iidae), rabbits (Leporidae), squirrels (Sciuridae), shrews(Soricidae), mice (Muridae), dogs (Canidae), bears (Ursi-dae), weasels (Mustelidae) and cats (Felidae). The passagewas two-way and is known as the Great AmericanInterchange.

The Applied Use of BiogeographicalRegions: Their Place in Conservation

Each biogeographical region contains a combination ofspecies, genera and families, many of which are endemic.Each has a distinctive character that, without conservationmeasures, stands to be greatly diminished or even lost.Natural biogeographical regions are threatened by humanactivities, and in particular by habitat loss and fragmen-tation and by the introduction of alien species (Sodhi and

10°N

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Huxley’s modificationof Wallace’s line

Wallace’s line

Weber’s lineWallacea

Lydekker’sline

SouthChina Sea

PacificOcean

100°E 120°E 140°E

Figure 5 Wallacea – the transition zone between the Oriental and

Australian faunal regions.

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Ehrlich, 2010). See also: Biodiversity – Threats; Conser-vation of Biodiversity; Conservation of Populations andSpecies; Ecological Consequences of Habitat Fragmen-tation; Natural Selection: Responses to Current (Anthro-pogenic) Environmental Changes

Habitat loss and fragmentation

The human species has transformed the globe to such anextent that only fragments, admittedly some large, of ori-ginal fauna and flora remain in most biogeographicalregions. Natural habitats are conserved inwildlife reserves,where efforts are made to preserve the indigenous faunasand floras. Threatened species and communities standan even better chance of survival if the wildlife reservesare linked by corridors. By the mid-nineteen eighties, 13western North American wildlife parks had lost 43%of their historical lagomorph (rabbits, hares and pikas),carnivore and ungulate species. But the Kootenay–Banff–Jasper–Yoho park system, which embodied significantconnections between wildlife reserves, maintained all itsoriginal mammal fauna (Newmark, 1987).

The old idea that species could be preserved in zoos is nolonger seen as a workable option. Zoos have their place inconservation, for example enabling the reintroduction ofnear-extinct species to the wild (Hosey et al., 2009), butmuch conservation effort now goes into protecting speciesin the surviving fragments of natural habitats. There is alsoa growing realisation that entire communities need con-serving, and not only ‘fashionable’ species like the tiger andorang-utan.

Human introductions

Humans are watering down the distinctiveness of bio-geographical regions by the introduction of alien species:they are homogenising the global fauna and flora. Take thecase ofNewZealand.Fifty-fourmammal species have beenintroduced to the island. Twenty camedirectly or indirectlyfrom Britain and Europe, 14 from Australia, 10 from theAmericas, six fromAsia, two from Polynesia and two fromAfrica. The package contained domestic animals forfarming and household pets and feral animals for sport orfur production. Farm animals included sheep, cattle andhorses. Domestic animals included cats and dogs. Sportinganimals included pheasant, deer, wallabies and rabbits.The Australian possum was introduced to start a furindustry. Wild boars and goats were liberated on NewZealand by Captain James Cook.Many other species wereintroduced – European blackbirds, thrushes, sparrows,rooks, yellow hammers, chaffinches, budgerigars, hedge-hogs, hares, weasels, stoats, ferrets, rats and mice.Of course, natural invasions of alien species do take place,but not, it would seem, at the human-induced ratesprevalent over the last couple of centuries. See also: BioticHomogenisation

Introduced species commonly have an adverse effectupon native species. The Indian mongoose (Herpestes

auropunctatus), introduced to various islands worldwide inthe hope of controlling rats and other vertebrate pests, hasled to the extinction of several native bird and reptilepopulations. Cats and rats introduced to islands have alsotended to have an inimical effect on native wildlife. Theinadvertent introduction of the sac fungus, Cryphonectria(Endothia) parasitica, into the United States around 1900led within 50 years to the near elimination of the Americanchestnut (Castanea dentata) from the native eastern hard-wood forests. See also: Invasion of Introduced Species

Summary

The world’s terrestrial animals and plants are grouped intofaunal and floral regions. Six faunal regions are recognisedtraditionally, though a modern scheme, constructed usinga numerical classification technique, identifies four regionsand 10 subregions. Six floral regions and 37 floral regionsare commonly distinguished. The floral and faunal regionsbear broad agreement with one another but displayimportant differences of detail. The natural faunas andfloras of biogeographical regions are unique. They areunder a severe threat from habitat loss and fragmentation,and from the introduction of new species by humans. Theirlong-term survival depends upon local and regional con-servation schemes.

References

Bohning-Gaese K, Gonzalez-Guzman LI and Brown JH (1998)

Constraints on dispersal and evolution of the avifauna of the

Northern Hemisphere. Evolutionary Ecology 12: 767–783.

Cox CB (2001) The biogeographic regions reconsidered. Journal

of Biogeography 28: 511–523.

Flynn JJ, Wyss AR and Charrier R (2007) South America’s

missing mammals. Scientific American 296(5): 68–75.

Good R (1974) The Geography of the Flowering Plants, 4th edn.

London: Longman.

Hosey G, Melfi V and Pankhurst S (2009) Zoo Animals: Behav-

iour, Management, and Welfare. Oxford: Oxford University

Press.

Kreft H and Jetz W (2010) A framework for delineating bio-

geographical regions based on species distributions. Journal of

Biogeography 37: 2029–2053.

Michaux B (1994) Land movements and animal distributions

in east Wallacea (eastern Indonesia, Papua New Guinea

and Melanesia). Palaeogeography, Palaeoclimatology, Palaeo-

ecology 112: 323–343.

Morrone JJ (2009) Evolutionary Biogeography: An Integrative

Approach with Case Studies. New York: Columbia University

Press.

Newmark WD (1987) A land-bridge island perspective on mam-

malian extinctions in western North American parks. Nature

325: 430–432.

Sclater PL (1858) On the general distribution of the members of

the class Aves. The Journal of the Linnean Society of London:

Zoology 2: 130–145.

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Smith CH (1983a) A system of world mammal faunal regions. I.

Logical and statistical derivation of the regions. Journal of

Biogeography 10: 455–466.

Smith CH (1983b) A system of world mammal faunal regions. II.

The distance decay effect upon inter-regional affinities. Journal

of Biogeography 10: 467–482.

Sodhi NS and Ehrlich PR (2010) Conservation Biology for All.

Oxford: Oxford University Press.

Takhtajan AL (1986) The Floristic Regions of the World, trans-

lated byTCrovello. Berkeley, CA: TheUniversity of California

Press.

Vane-Wright RI (1991) Transcending the Wallace Line: do the

western edges of the Australian region and the Australian plate

coincide? Australian Systematic Botany 4: 183–197.

WallaceAR (1876)TheGeographicalDistribution ofAnimals; with

a Study of the Relations of Living and Extinct Faunas as Eluci-

dating the Past Changes of the Earth’s Surface, 2 Vols. London:

Macmillan.

Further Reading

Cox CB and Moore PD (2009) Biogeography: An Ecological

and Evolutionary Approach, 8th edn. Oxford: Blackwell.

Feldhamer GA, Drickamer LC, Vessey SH, Merritt JF and

Krajewski CW (2007) Mammalogy: Adaptation, Diversity,

Ecology, 3rd edn. Baltimore: Johns Hopkins University Press.

Flynn JJ (2009) Splendid isolation: South America was an island

for millions of years, fostering an evolutionary explosion of

unique mammal species. Natural History 188: 26–32.

Huggett RJ (2004) Fundamentals of Biogeography, 2nd edn.

London/New York: Routledge.

Lomolino MV, Riddle BR, Whittaker RJ and Brown JH (2010)

Biogeography, 4th edn. Sunderland, MA: Sinauer Associates.

WilsonDE andReederDM (2005)Mammal Species of theWorld:

A Taxonomic and Geographic Reference, 3rd edn. Baltimore:

Johns Hopkins University Press.

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