The Zoogeographical Realms
Geography is the study of Earth’s regions, lands, features, properties, and other relationships. The science of biogeography is to study geographical aspects of plants and animal life, especially their distribution in different parts of Earth.
Biogeography is further divided into two branches named Phytogeography and Zoogeography. Phytogeography concerns itself with the geographical distribution of plants and Zoogeography is the scientific study of the distribution of animals and other related geographical aspects.
Earth is full of life. Deserts, mountains, forests, beaches, lakes, rivers, oceans, prairies, and so on, every part of Earth is inhabited with a unique form of life. To study, classify and understand them, there is a need for the distribution of regions and fauna living in them.
Researches and studies show that the distribution of life on Earth is by no means a uniform one. Due to different climate patterns and other causes, there are unusual and odd instances of isolated distributions.
Today, it is clearly understandable that the distribution of life on Earth not only depends on climate or suitability to the environment but this distribution is governed by many other factors and laws.
The whole arrangement of animal distribution on Earth led to the initiation and setting up of the zoogeographical realms.
“Zoogeographical realms are the regions established on the presence and absence of fauna.”
“A region on Earth having fauna, more particularly mammals which possess unique characters distinguishing them from other areas.”
History of Zoogeographical Realms
In 1857, Dr. P.L. Sclater who was the Secretary of Zoological Society, London first attempted to divide the Earth into a number of life regions. His division was based upon the distribution of birds. The region he proposed were: 1) Palaearctic 2) Ethiopian 3) Indian 4) Australian 5) Nearctic and 6) Neotropical.
In 1868, Huxley proposed the division of Earth into two basic regions, a northern called ARCTOGAEA and a southern called NOTOGAEA. He placed Palaearctic, Ethiopian, Indian, Nearctic regions of Sclater into ARCTOGAEA. The remaining was placed in NOTOGAEA and divided into three provinces New Zealand, Australasia, and Austro-Columbia. This was disproportionate so discarded,
In 1876, Alfred Russel Wallace, who is the father of modern zoogeography published a classical paper on “The geographical distribution of Animals” which still is the standard authority on the subject. He agreed with Sclater divisions, but divisions of Wallace were based on the distribution of mammals. And he suggested names other than earlier names, Oriental substituted for Indian, African substituted for Ethiopian. As earlier names suggested countries, not zoogeographical regions.
Reasons for selecting Mammals as a distribution unit
- The abundance of fossils of mammals shows more features of the past ages’ distribution.
- The limited dispersal, greater power of adaptations, less dependence on the particular types of food or specific conditions for existence made classifications more accurate.
- Mammals can easily be monitored, controlled, observed, and examined. And are most conspicuous among all.
The modern classification of land masses into zoogeographical realms has been modified many times since Wallace’s time. But Wallace’s classification is still considered to be the most appropriate one. The modern zoogeographical realms are based on Wallace’s classification (1876) and Darlington (1957).
The realms described by them are all separated by distinctive barriers such as oceans, rivers, lakes, mountains, deserts, etc. They all have different climates and unique environmental conditions.
Wallace classified three realms into six zoogeographical regions and their subdivisions. These are as follows:
1. Realm MEGAGEA
Subregions: European, Mediterranean, Siberian, and Manchurian.
Subregions: Californian, Allegheny, Canadian, Rocky Mountains.
AFRICAN = ETHIOPIAN REGION
Subregions: East Africa, South Africa, West Africa, and Malagasy.
Subregions: Indian, Indochinese, Ceylonese, Indo-Malayan.
2. Realm NEOGEA
Subregions: Brazilian, Mexican, Chilean, Antillean.
3. Realm NOTOGEA
Subregions: Austro-Malayan, Australian, Polynesian, New Zealand.