Zoogeographical Realms – Definition, Meaning and Types

What is Zoogeographical Realms?

• Zoogeographical realms are regions on Earth that are defined based on the presence or absence of specific organisms. These realms provide a framework for understanding the distribution of various species across the planet. The concept of zoogeographical realms was first introduced by P. L. Sclater in 1857, who divided the Earth’s geographical areas into six parts based on the distribution of birds.
• Later, in 1876, Alfred Russel Wallace expanded on Sclater’s work and published a paper on zoogeographical realms. Wallace’s study included not only birds but also all terrestrial vertebrates and invertebrates. He retained the basic idea of six areas proposed by Sclater but made a slight modification by renaming the Indian region to the Oriental region.
• Wallace’s division of zoogeographical realms was characterized by distinctive barriers that separated each realm from the others. These barriers are depicted as dotted lines on world maps and are commonly known as Wallace’s line. They represent significant transitions in species distribution and highlight the unique biodiversity found in each realm.
• The concept of zoogeographical realms and Wallace’s line have been influential in the field of biogeography. By understanding the distribution patterns of organisms across these realms, scientists can gain insights into evolutionary history, ecological processes, and environmental factors that shape biodiversity.
• It is important to note that the specific boundaries and definitions of zoogeographical realms may vary depending on different scientists and their research findings. Nonetheless, the concept remains a valuable tool for studying and categorizing the Earth’s biodiversity based on geographic patterns.

Types of Zoogeographical Realms

1. Palaearctic Realm

• Geographical Boundary:
  • The Palaearctic Realm encompasses the entirety of Europe, the northern part of Africa, and the Asian Himalayas and Nan Ling Range of China.
• Sub-divisions:
  • European Sub-region:
    • Includes northern and central Europe, as well as the Black Kokesus region.
  • Mediterranean Sub-region:
    • Encompasses parts of Africa, Asia, and Europe, including regions like the Arabian Peninsula, Afghanistan, and Baluchistan.
  • Siberian Sub-region:
    • Consists of the northern part of the Himalayas, specifically the northern regions of Asia.
  • Manchurian Sub-region:
    • Includes Mongolia, Korea, Manchuria, and Japan.
• Climatic Condition:
  • The Palaearctic Realm experiences extreme cold in Siberia and extreme heat in the Sahara Desert, representing characteristic climates of the region.
• Ecological Condition:
  • The realm showcases various ecological conditions, such as deciduous forests, large grasslands, coniferous forests, mixed forests, and tundra areas.
• Characteristic Vertebrate Fauna:
  • Fish:
    • Common freshwater fish species include carp, salmon, pike, and sticklebacks.
  • Amphibia:
    • Amphibians found in the Palaearctic Realm include the European Salamander, Proteus, Hynobius, Bombinator, Alytes, and Didocus, among others.
  • Reptiles:
    • Reptilian species present in this realm include the sand boa, lizard (such as Trigonophis), and alligator.
  • Birds:
    • Bird species found in the Palaearctic Realm include the Arctic tern, pheasants, wrens, finches, warblers, and geese, among others.
  • Mammals:
    • The realm is home to various mammalian species, including the endemic families Seluinidae and Ailuropodie. Other mammals found in the Palaearctic Realm are porcupines, dogs, wild asses, European bison, polar cats, deer, and more.

2. Nearctic Realm

• Geographical Boundary:
  • The Nearctic Realm spans the entire North American continent, extending from northern regions to Mexico. It also includes Greenland in the east and the Aleutian Islands in the west.
• Sub-divisions:
  • Californian Sub-region:
    • Encompasses areas such as Vancouver Island in British Columbia, Nevada, and parts of the Cascade Hill region. It is known for its low biodiversity compared to other sub-regions.
  • Rocky Mountain Sub-region:
    • Located on the eastern side of California, this sub-region features a high and rocky mountain range. It is rich in zoological diversity within the Nearctic Realm.
  • Allegheny Sub-region:
    • Situated to the east of the Rocky Mountain Sub-region, with its northern part bounded by the Great Lakes. This sub-region exhibits moderate zoological characteristics.
  • Canadian Sub-region:
    • This sub-region includes North America and Greenland, but it is not particularly renowned for its animal diversity.
• Climatic Condition:
  • The Nearctic Realm experiences extreme cold and hot climates, similar to the Palaearctic region.
• Ecological Condition:
  • Prominent ecological zones in the Nearctic Realm include deciduous forest ranges, vast grasslands, coniferous forests, dry lands, and tundra regions.
• Characteristic Vertebrate Fauna:
  • Fishes:
    • Common fish species found in the Nearctic Realm include Lepisosteus, Polydon, Acipenser, and various types of perches.
  • Amphibia:
    • Amphibians in this realm include species such as Siren, Amphiuma, Cryptobranchus, Ambystoma, Ascaphys, and Axolotl larvae. Most of them belong to the order Caudata.
  • Reptiles:
    • Prominent snakes in the Nearctic Realm include Conophis, Chilomeniscus, Pituophis, and Farancia. Lizards such as Phrynosoma and Uta are also found, along with turtles like Aromochelys and Chelydra.
  • Birds:
    • The bird species in this realm encompass a wide range, including turkeys, pelicans, crows, cuckoos, pigeons, saras, swans, kites, rails, owls, hawks, and more. Many of these birds are migratory.
  • Mammals:
    • Mammalian fauna in the Nearctic Realm includes species such as Didelphis, Armadillos, Caribou, pronghorns, shrews, moles, bears, wolves, monkeys, deer, bats, goats, musk oxen, bison, and others. The mammalian families Aplodontidae and Pronghorn are endemic to this region.

3. Neo-tropical Realm

• Geographical Boundary:
  • The Neo-tropical Realm includes South and Central America, lower Mexico, and the West Indies. It is connected to the Nearctic region via the Central American isthmus, and its other parts are bordered by the sea.
• Sub-divisions:
  • Chilean Sub-region:
    • Encompasses the western part of South America, including Peru, Bolivia, and the Andes mountain range. It has a relatively low faunal content.
  • Brazilian Sub-region:
    • Covers the entirety of Brazil and extends up to the Panama Canal. This sub-region is highly rich in faunal composition.
  • Mexican Sub-region:
    • Situated within North and South America, specifically the northern side of the Panama isthmus. It contains some important fauna.
  • Antillean Sub-region:
    • Includes the entire West Indies, excluding Trinidad and Tobago. This sub-region is characterized by a limited amount of animal content.
• Climatic Condition:
  • Most parts of the Neo-tropical Realm are covered by tropical drylands. The southern part of America experiences a temperate climate.
• Ecological Condition:
  • The Amazon valley is dominated by tropical rainforests. The temperate regions consist of savannahs and grasslands. The western part of South America is dry and exhibits a desert-like ecosystem. Argentina is predominantly composed of grasslands.
• Characteristic Vertebrate Fauna:
  • Fishes:
    • The region is home to 120 genera of fishes from three families: Polycentridae, Gymnotidae, and Trigonidae. Notable fish species include Lepidosiren, eel, and catfish.
  • Amphibia:
    • Amphibians found in the Neo-tropical Realm include Caecilia, Siphonopsis, Hyla, salamanders, frogs, and toads.
  • Reptiles:
    • Reptilian species such as Dromicus, Boa, Epicrates (snakes), Gecko, alligators, and Chelys are present in the region.
  • Birds:
    • The Neo-tropical Realm boasts a total of 700 genera of birds. Some notable bird species include tenemus, screamus, whatgin, to wean, thrush, and parakeets.
  • Mammals:
    • The region is home to 32 families of mammals. Important species include opossums, caenolestes, sloths, armadillos, rodents, American tapirs, bats, spider monkeys, llamas, and more.

4. Ethiopian Realm

• Geographical Boundary:
  • The Ethiopian Realm includes the southern part of the Tropic of Cancer, most of the African mainland, the southern part of Arabia, and Madagascar.
• Sub-divisions:
  • East African Sub-region:
    • This sub-region comprises the hot and dry regions of Africa and Arabia.
  • West African Sub-region:
    • The western part of the Ethiopian region extends up to the Congo in this sub-region.
  • South African Sub-region:
    • The entire southern part of Africa falls within this sub-region.
  • Malagasy:
    • The sub-region includes the entirety of Madagascar.
• Climatic Condition:
  • The majority of the Ethiopian Realm experiences a mainly temperate climate, but remains hot throughout most of the year.
• Ecological Condition:
  • Areas along the equinoctial line and West Africa possess rainforests along the banks of large rivers. Most other parts of the region are covered by dry deciduous forests. The northern and southern parts have transformed into deserts.
• Characteristic Vertebrate Fauna:
  • Fishes:
    • Catfish, lungfishes (Protopterus, Polypterus), and several freshwater fish species are present in the region.
  • Amphibia:
    • Xenopus and several species of caecilians can be found, while the group caudata is entirely absent.
  • Reptiles:
    • Prominent snake species include Leptorhynchus, Ramnophis, etc. Among lizards, Monotrophis, Cordylus, Agama, Chameleon, and others are notable.
  • Birds:
    • A total of 67 avian families are recorded in the Ethiopian Realm. Some important bird species include ostrich, cuckoo, parakeet, eagle, kite, pigeon, hornbill, and more.
  • Mammals:
    • There are 51 recorded families, with 15 being endemic to the region. Remarkable mammalian species include zebra, gorilla, antelope, leopard, two-horned rhinoceros, hippopotamus, lemur, gnu, baboon, lion, giraffe, chimpanzee, and loxodonta.

5. Oriental Realm

• Geographical Boundary:
  • The Oriental Realm includes most of the Asian countries situated to the southern side of the Himalayas. It encompasses India, Burma, Indo-China, Malay, Sumatra, Java, Bali, Borneo, Philippines, and more.
• Sub-divisions:
  • Indian Sub-region:
    • The entire Indian subcontinent falls within this sub-region. It is further divided into various divisions based on the distribution of mollusks, reptiles, birds, and mammals.
      • Dry and semidry area of Northern India
      • Western side of Himalaya
      • Southern part of Burma
      • Plateau of Ganges
      • Southern India below 20° latitude
      • Ganga plateau and area above 20° latitude
      • Tribankur
      • Ceylon
      • Nicobar islands
      • Andaman islands
• Ceylonese Sub-region:
  • This sub-region includes parts of the Indian peninsula and Sri Lanka.
• Indo-Chinese Sub-region:
  • South China, Burma, Thailand, and Indo-China fall within the borders of this sub-region.
• Indo-Malayan Sub-region:
  • This eastern part of the Oriental Realm includes Malay and the East-Indies islands.
• Climatic Condition:
  • The majority of the Oriental Realm experiences a temperate atmosphere, with an annual rainfall of more than 1500 mm.
• Ecological Condition:
  • The eastern part of the region contains dense rainforests, while the western part has a desert-like ecosystem. Other parts have moderate forest cover.
• Characteristic Vertebrate Fauna:
  • Fishes:
    • Various types of carp, catfish, notopteridae, osteoglocid, cipriniformes, and more.
  • Amphibians:
    • Varieties of anurans, some salamanders, and caecilians are present.
  • Reptiles:
    • Various types of snakes such as vipers, pit vipers, kraits, etc. Lizards including Gekko, Aagamid, Varanus, Chameleon, Crocodiles, and Gavialis are found. The Platysternidae family of turtles is also present.
  • Birds:
    • Pigeons, owls, finches, pheasants, peacocks, saras, and more.
  • Mammals:
    • Srew, rabbit, dog, cat, boar, rodents, flying lemur, elephants, ox, tiger, orangutan, gibbon, tapir, pangolin, Rhinoceros unicorns, and other important members. Out of 30 families, only 4 are endemic to the region.

6. Australian Realm

• Geographical Boundary:
  • The Australian Realm includes Australia, New Zealand, New Guinea, Tasmania, and some adjacent islands.
• Sub-divisions:
  • Austro-Malayan Sub-regions:
    • This sub-region encompasses the Malay Archipelago, including New Guinea, the Moluccas, and the Solomon Islands.
• Australian Sub-region:
  • Tasmania and Australia are part of this sub-region.
• Polynesian Sub-region:
  • Polynesia and the Sand-wick Islands are included in this sub-region.
• New Zealand Sub-region:
  • New Zealand, Norfolk Island, Auckland, Campbell, and Macquarie Islands comprise this sub-region.
• Climatic Condition:
  • The Australian Realm experiences both hot and temperate climates. The average annual rainfall is 75 mm.
• Ecological Condition:
  • Prominent ecological characteristics include rainforests, grasslands, and eucalyptus forests.
• Characteristic Vertebrate Fauna:
  • Fishes:
    • Neoceratodus lungfish, Osteoglocidos, Gadopcidae, and other fish species are present.
• Amphibians:
  • The Xenorhinidae family is found in New Guinea. Other important amphibians include Pseudophryne, Pachybatrachus, Helioporus, and Pelodyrus. A total of 11 families are recorded.
• Reptiles:
  • Important snake families include Phithonidae and Elapidae. Prominent lizards include Pizopidae, Apracidae, and Liadidae. The Sphenodon of the Rhynchocephalidae family is a famous relic reptile found in New Zealand.
• Birds:
  • Casuaries, lyrebirds, magpies, emus, kiwis, scrub birds, and bowerbirds are important members of this region. A total of 906 species of birds have been recorded.
• Mammals:
  • Remarkable mammal species include the ornithorhynchus (a marsupial), Tachyglossus (anteater), kangaroo, dasyures, dendrolagus (climbing kangaroo), Petaurus (flying opossum), and wolves.

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