This document provides a history of the field of zoogeography, summarizing the key contributions of various scientists. It discusses early attempts to divide the world into zoogeographical regions in the late 19th century by Schmarda and Sclater. Sclater's 1858 divisions of the world into six regions based on bird distributions formed the basis for modern zoogeography. The document then outlines later modifications and enhancements to zoogeographical schemes by scientists such as Wallace, Darlington, and others. It also discusses the impacts of plate tectonics theory and the vicariance model on modern biogeography.

1. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
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History of Zoogeography
Zoogeography is a branch of Biogeography that deals with the study of past and present
distribution of animals on Earth. Over the centuries, this science has evolved due to the
contribution of many scientists, some notable efforts are discussed below:
First Attempt at the Biogeographic Division of Earth
The first attempt to include all animal life, marine and terrestrial, in a single zoogeographic
scheme was by Ludwig K. Schmarda in his volume entitled Die Geographische
Verbreitung der Tierre (1885). He divided the world into 21 land and 10 marine realms.
"A zoogeographical region/realm is a sub-division of the Earth having a unique fauna, i.e.
species that are found only in that area.”
Contributions of Philip Lutley Sclater
It was Philip Lutley Sclater who divided the terrestrial world into the biogeographic regions
that, essentially, are still in use today. This was done in 1858 in a small paper entitled On
the General Geographical Distribution of the Members of the Class Aves. Despite the fact
his scheme was based only on the distributional patterns of birds, Sclater’s work proved
to be useful for almost all groups of terrestrial animals. This has served to emphasize that
biogeographic boundaries, found to be important for one group, are also apt to be
significant for many others. He divided the surface of the earth into six regions:
 Palearctic Region (Europe)
 Ethiopian Region (Africa)
 Indian Region (South Asia)
 Australian Region (Australia, Tasmania & New Guinea)
 Neotropical (South America)
 Nearctic (North America)

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According to him, Palearctic, Ethiopian, Indian and Australian regions were grouped into
a single region known as Paleogaea / Old World (eastern half of the world’s
zoogeographical regions). Nearctic and Neotropical regions were grouped into a single
region known as Neogaea / New World (western half of the world’s zoogeographical
regions).
Contributions of Thomas Henry Huxley
In 1868, Thomas Henry Huxley proposed the division of the surface of Earth into two
primary regions called Arctogaea (northern region) and Notogaea (southern region).
Arctogaea is comprised of Palearctic, Nearctic, Ethiopian, and Indian regions. Notogaea
is comprised of Neotropical and Australian regions. His scheme was regarded as invalid
and disproportionate and was later discarded.
Natural Selection & Zoogeography
When Charles Darwin visited the Galapagos Islands in 1835, he was struck by the
distinctiveness, yet basic similarity, of the fauna to that of mainland South America. When
Alfred Russel Wallace traveled through the Indo-Australian Archipelago, some 20 years
later, he was puzzled by the contrasting character of the island faunas, some with
Australian relationships and others with southeast Asian affinities. After considerable
thought about such matters, each man arrived at a theoretical mechanism – natural
selection to account for evolutionary change.
The key for both Darwin and Wallace was the realization that distributional patterns had
evolutionary significance. The announcement of their joint theory by Darwin and Wallace
in 1858 in the Journal of the Linnean Society of London and, especially, the publication
of Darwin's Origin of Species in 1859, changed the thinking of the civilized world. In
discussing biogeography from the viewpoint of evolutionary change, Darwin made three
important points:

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He emphasized that barriers to migration allowed time for the slow process of modification
through natural selection. He considered the concept of single centers of creation to be
critical, that is, each specieswas first produced in one area only and from that center, it
would proceed to migrate as far as its ability would permit.
He noted that dispersal was a phenomenon of overall importance. Regarding the third
point, Darwin observed that oceanic islands were generally volcanic in origin and must
have accumulated their biota by dispersal from some mainland sources. He felt
that the presence of alpine species on the summits of widely separated mountains could
be explained by dispersal having taken place during the glacial period when such forms
would have been widespread.
More importantly, he suggested that the relationships that biologists were then finding
between the temperate biotas of the northern and southern hemispheres were attributable
to migrations made through the tropics during the glacial period when world temperatures
were cooler. Finally, he noted that the preponderant interhemispheric migratory
movement had been from north to south and suggested that this was due to the northern
forms having advanced through natural selection and competition to a higher stage of
dominating power.
Contributions of Joseph D. Hooker
When Darwin was going through the long process of formulating his theory, Joseph D.
Hooker was one of his closest confidants. Hooker was particularly interested in the
southern hemisphere botany. Hooker felt that Darwin was perhaps too dependent on
dispersal in accounting for disjunct relationships.
In describing the flora of New Zealand in 1853, Hooker speculated on the possibility that
the plants of the Southern Ocean were the remains of a flora that had once been spread

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over a larger and more continuous tract of land than now exists in that part of the world
(fragmentation of a distribution to produce discontinuity).
The Geographic Distribution of Animals by Alfred Russel Wallace
While Darwin went on to investigate many other aspects of evolutionary change, Alfred
Russel Wallace applied himself primarily to biogeography. Finally, in 1876, Wallace
published his monumental two-volume work: The Geographical Distribution of Animals.
In that work, he reached several conclusions about biogeography that are still worth
reviewing. For example, he pointed out that:
 Paleoclimatic studies are very important for analyzing extant distribution patterns.
 Competition, predation, and other biotic factors play important roles in the
distribution, dispersal, and extinction of animals and plants.
 Discontinuous ranges may come about by extinction in intermediate areas or
patchiness of habitats.
 Disjunctions of genera show greater antiquity than those of a single species, and
so forth for higher categories.
 The common presence of organisms not adapted for long-distance dispersal is
good evidence of past land connections.
 When two large landmasses long separated are reunited, extinction may occur
because many organisms will encounter new competitors.
 Islands may be classified into three major categories, continental islands recently
set off from the mainland, continental islands long separated from the mainland
(also known as ancient islands), and oceanic islands of volcanic and coralline
origin.
 Studies of island biotas are important because the relationships among
distribution, speciation, and adaptation are easier to see and comprehend.

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Wallace chose mammals as model organisms in his book, this was due to several
reasons:
 The abundance of mammalian fossils indicates more features of the distribution in
the past than any other group of animals.
 Careful studies of the fossils of mammals and the knowledge of the living mammals
give their identification and classification more accurately.
 The limited means of dispersal in mammals and their high power of adaptation
andorganization gives less dependence upon a particular kind of food or particular
kind of environmental conditions.
 Mammals are very prominent and can be easily collected, monitored, observed,
and examined.
Wallace’s Division of Zoogeograhical Realms
Alfred Russel Wallace, who is referred to as the “father of zoogeography”, followed the
same classification as that of P. L. Sclater but he introduced the Oriental region instead
of the Indian region. The six zoogeographical regions and their sub-regions (four each)
given by Wallace are as follows:
 Palearctic Region – Sub-regions: European, Mediterranean, Siberian and
Manchurian.
 Ethiopian Region – Sub-regions: East Africa, West Africa, South Africa, and
Malagasy.
 Oriental Region – Sub-regions: Indian, Ceylonese, Indo-Chinese, and Indo-
Malayan.
 Australian Region – Sub-regions: Austro-Malayan, Australian, Polynesian, and
New Zealand.
 Neotropical Region – Sub-regions: Chilean, Brazilian, Mexican, and Antillean.

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 Nearctic Region – Sub-regions: Californian, Rocky Mountains, Alleghany, and
Canadian.
Wallace did considerable traveling in the Indo-Australian region and was particularly
concerned about the location of the dividing line between the Oriental and Australian
faunas. Wallace, by 1863, had decided that the line should run from east of the Philippines
south between Borneo and Celebes and then between Bali and Lombok. It was illustrated
in his 1876 work and later in his book Island Life in 1880. Although Wallace, in his 1910
book The Worm of Life changed his mind about the affiliation of Celebes, his original line
is the one generally called “Wallace's Line”.
Modifications / Enhancements made to Wallace’s Scheme
Following the publication of Wallace’s works, many biogeographers repeated his
distribution plan without any major new interpretations. But some scientists did expand
Wallace’s work further, some notable mentions are (Darlington’s work has been
discussed in a separate heading):
Angelo Heilprin (1887): He suggested the union of the Nearctic and Palearctic region into
a huge Holarctic realm due to the similarity of the flora and fauna. In his system, there
were five divisions: (1) Holarctic, (2) Ethiopian, (3) Oriental, (4) Australian, and (5)
Neotropical regions.
Édouard Louis Trouessart (1890): He introduced two more regions in addition to
Wallace’s six: Arctic and Antarctic regions (although Wallace’s six regions have remained
the center of focus).
K. P. Schmidt (1954): He divided the world into three regions: (1) Arctogaea (Holarctic,
Ethiopian, Oriental), (2) Notogaea (Australian), and (3) Neogaea (Neotropical).
Contributions of Philip Jackson Darlington Jr.

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In 1957, Philip J. Darlington Jr. published his book – Zoogeography: the Geographical
Distribution of Animals, although this book was based only on patterns demonstrated by
the terrestrial and freshwater vertebrates, it represented an important milestone because
it was the first time in the 20th century that all of the information about those animal groups
had been gathered together.
Since the data on fossil vertebrates are, in general, better than those for the invertebrate
groups, Darlington's book had great significance for historical biogeography. Darlington
(1957) emphasized that the major worldwide patterns of vertebrate animals indicated a
series of geographical radiations from the Old World tropics. Such radiations were
considered to take place because competitively dominant animals were continually
moving out from their tropical centers of origin.
He presented his schemes for the division of earth’s zoogeographical regions, which were
a modification of Wallace’s scheme:
FIRST SCHEME
Realm Megagea (Arctogea): The main part of the world
 Ethiopian Region: Africa (except the northern corner), with part of southern Arabia
 Oriental Region: tropical Asia, with associated continental islands
 Palearctic Region: Eurasia above the tropics, with the northern corner of Africa
 Nearctic Region: North America, excepting the tropical part of Mexico
Realm Neogea
 Neotropical Region: South and Central America with the tropical part of Mexico
Realm Notogea
 Australian Region: Australia, with New Guinea, etc.

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SECOND SCHEME
 Climate-limited regions: Palearctic & Nearctic Regions
 Main regions of the Old World tropics: Oriental & Ethiopian Regions
 Barrier-limited regions: Neotropical & Australian Regions
Impacts of the Theories of Continental Drift & Plate Tectonics
Between 1910 and 1912, scientists such as Frederick B. Taylor, H. D. Baker, and Alfred
L. Wegener had all advanced views about continental drift similar to those that are held
today. However, at that time, the earth’s crust was almost universally considered to have
a solid structure without movement. Between 1915 and 1929, Wegener published four
editions of his book – The Origin of Continents and Oceans.
These works created considerable controversy but most geologists and geophysicists
were still not convinced. Research into paleomagnetism then began to offer some
supporting evidence for drift. In 1960, Harry H. Hess suggested that the sea floors crack
open along the crest of the mid-ocean ridges and that new seafloor forms there and
spreads apart on either side of the crest.
Robert S. Dietz named this process sea-floor spreading and coupled with it the
suggestion that old seafloor is absorbed beneath zones of deep ocean trenches and
young mountains. J. Tuzo Wilson (1963, 1973) noted that oceanic islands tended to
increase in age away from the mid-ocean ridges and that certain “hot spots” existed where
strings of volcanic islands had been formed. These and other discoveries led to the
modern view of plate tectonics which holds that the earth’s crust is divided into a mosaic
of shifting plates in which the continents are embedded.
We now have many reconstructions of continental relationships covering the last 700
million years. The plate-tectonic revolution in earth science had a gradual but decisive
effect on biogeography. Previously, it had been necessary to discuss the historical

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relationships of the biogeographical regions and their biotas within the framework of
stable continents, but now biogeographers were released from this restraint.
The Vicariance Model
Vicariance refers to the biogeographic patterns produced by a particular kind of allopatric
speciation in which a geographic barrier develops so that it separates a formerly
continuous population (it was promoted in the 1970s). This distinguishes vicarianism from
the kind of allopatric speciation which takes place as the result of migration or dispersal
of individuals across an existing barrier to colonize the other side.
The proponents of vicarianism emphasized that it was really vicariance that produced
geographical differentiation and multiplication of species. In the best explanation of the
mechanics of vicarianism, Croizat et al. (1974) stated, “The existence of races or
subspecies that are separated by barriers (vicariance) means that a population has
subdivided, or is subdividing, not that dispersal has occurred, or is occurring across the
barriers.” The vicariance model places two important restrictions on the development of
biogeography as a field of research:
It recognizes only a certain kind of allopatric speciation as being of historical importance.
It does not recognize that centers of origin (as proposed by Darwin – species originate in
a specific place and then disperse to new regions) exist since, to do so, would admit that
dispersal has taken place.
Allopatric speciation via dispersal can and does take place, the speciation problem is not
that simple. There is a growing body of evidence showing that both parapatric and
sympatric speciation can take place in nature. Neither of the latter two processes require
geographic barriers. Similarly, the idea of centers of origin is also widely supported by
modern evidence.
Modernization of Zoogeography – Eclectic Approach

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In light of paleontological evidence, it can be said that both dispersal and vicarianism
have each played an important role in historical biogeography. Sometimes the creation
of a barrier will result in the interruption of the range of a species or a species complex
(vicariance). For example, when the Isthmus of Panama was finally completed in the
Pliocene, it separated the tropical marine environment of the New World into two parts,
one inhabiting the Eastern Pacific and the other the Western Atlantic.
But, at the same time, the isthmian connection provided a dispersal corridor between
North and South America for terrestrial and freshwater organisms, also with profound
evolutionary (and ecological) consequences. Similarly, when the land connection across
the Bering Strait was first made in the late Cretaceous, it separated the marine
populations of the Bering Sea-Arctic Ocean but connected terrestrial North America to
Asia. The tectonic uplift of a mountain range can constitute an important barrier for
lowland forms but simultaneously may present a migratory corridor for species of the high-
altitude biota.
Dispersal is an everyday occurrence undertaken by succeeding generations of almost all
species while vicarianism is an event of much greater rarity since it must involve the
creation of a barrier to separate existing populations. For the past 20 years, a significant
portion of the theoretical literature on biogeography has been devoted to the argument
about the efficacy of vicarianism compared to dispersalism.
Biogeographers must attempt to appreciate the biosphere as a whole instead of
concentrating too heavily on a single habitat. It is time to discard preconceptions about
what might have happened in the history of a given taxon. Let us use the clues that can
be found within the relationships of the group itself and in the history of its territory. This
is eclectic biogeography and it means freedom from preconceived ideas.