Zoogeography

**Arosa Hya** · 11-11-2015, 08:42 PM

Zoogeography

Zoogeography is the branch of the science of biogeography that is concerned with the geographic distribution (present and past) of animal species.

Branches of Biogeography
Geography has two branches; i) Phytogeography ii) Zoogeography
Phytogeography
It deals with the study of distribution of plant across the world in the past and present.
Zoogeography
It is subjected to the distribution of animals in the past, present and future, their evolutionary history and affinities among different regions of the world on the basis of their fauna. The country which is inhabited by a given animal is called its area of distribution, its habitat or locality.

Branches of Zoogeography
Zoogeography has two main branches i.e. ecological zoogeography and historical zoogeography. The ecological zoogeography investigates the role of current day biotic and abiotic interactions in influencing animal distributions and the historical geography are concerned with historical reconstruction of the origin, dispersal, and extinction of taxa.

Zoogeographical Regions
The world has been divided into six regions on the basis of distribution of mammals. The brief history of this division as follows;

Sclater's Regions
The first real attempt to divide the earth in to regions corresponding with the range of its inhabitants is that of Sclater. His results were obtained entirely from a consideration of the Passerine and some of the Picarian birds. Nevertheless the regions thus formed were found applicable to other groups and they have been for the most part accepted.
Sclater divided earth into regions mainly upon the distribution of Passerine birds; but later upon the geographical distribution of the Mammalia he applied the same regions for the purposes of tabulating the distribution of that group of animals also. In considering the distribution of the existing Mammalia four salient facts are at once apparent.
(1) Australia has both Monotremes and Marsupials.
(2) America has Marsupials but no Monotremes.
(3) The remainder of the world has Monodelphian Mammals only.
(4) New Zealand has no Mammals at all.

On this basis Sclater divided the world as follows:
I. Land where Monodelphs only occur; no Marsupials or Monotremes. Europe, Asia, Africa, Asiatic islands down to Wallace's line, North America. This land may be called Arctogcea.
II. Land where Monodelphs and Marsupials occur; no Monotremes. America south of the' Isthmus of Tehuantepec. This land may be called Dendrogwa.
III. Land where Marsupials prevail; no Monodelphs but rodents and bats; Monotremes. Australia. This may be called Antarctogcea.
IV. Land without Mammals (except bats). New Zealand and the Pacific islands. This land may be called Ornithogcea.
Arctogaea is then subdivided into the well-known Palaearctic, Ethiopian, Indian and Nearctic regions. But it is pointed out that these sections are not equal to the remaining and undivided Antarctogaea and Dendrogaea. The Ornithogaea is necessarily left out of consideration altogether, as it contains no Mammals.

Huxley's Regions
A study of the distribution of the Alectoromorpha led Prof. Huxley to suggest a different division of the world into regions. Australia and some of the islands to the north, along with South and Central America; this tract of the earth's surface he termed Notogaea, the part lying to the north being called Arctogaea.
The region of Notogaea where Ungulates are scarce, is again divided by Prof. Huxley into three divisions, which he names Austro-Columbia, Australia and New Zealand.
The most obvious criticism which has been applied is that they are quite out of proportion. This is particularly the case with New Zealand, which has so few types of great importance as compared with Austro-Columbia.

Wallace Considerations
Wallace urges the retention of the Sclaterian regions for the following three principal reasons:
(1) They are founded upon and approximate to the great primary divisions of the earth, which there is reason to believe have been permanent during considerable geological periods.
(2) They are rich and varied in all the main types of life.
(3) They possess great individuality; whether exhibited by the possession of numerous peculiar species, genera, or families, or by the entire absence of general, or families which are abundant and wide-spread in some of the adjacent regions.
Wallace suggested that the regions should be based on the class Mammalia whose distribution is found in all Zoological regions. The reasons for this, according to Wallace are following:
(1) They are dependent for their means of dispersal upon continuity of land. At least wide seas would be impassable.
(2) They are (with the exception of the bats which fly and might therefore be subject to gales, and the mouse tribe which might be conveyed in ships) too large to be carried accidentally across seas which they could not traverse by their own unaided efforts.
(3) Again they are so highly organized as to be largely independent of other animals; though both purely carnivorous and purely vegetarian forms exist there is for the most part no dependence upon any particular kind of animal or plant as food, such as we meet with for example among the insects. Or where there is a restriction in the matter of diet as in the case of the anteaters both of the old and new worlds the food is universally found.
(4) The Mammalia form a group which is fairly well known anatomically, we can therefore form a tolerably correct judgments to their mutual relationships. That this is the case is shown by the absence of any differences of opinion as to the outlines of the main subdivisions of the family.
(5) The last argument favorable to the Mammalia is the fact that we have a better knowledge of extinct forms than we have of any other existing group. It is perfectly true that this knowledge will bear increasing and that it is practically limited to the extinct genera of Europe and North America with certain parts of South America and India. But after all compared with other groups the knowledge is undoubtedly considerable.
After reviewing the distribution of mammals earth has been divided into six regions which are indeed the modified form of Sclater’s division. In this the Indian Region has been named as Oriental Region. These regions are;
I. The Palaearctic region.
II. The Nearctic region.
III. The Ethiopian region.
IV. The Oriental region.
V. The Neotropical region.
VI. The Australian region.