Bio-Geographical Classification of the World
Environment & Ecology › Biodiversity Basics and Classification · Topic 6.3
Biogeographic classification divides the world into regions according to the distribution of plants and animals. Alfred Russel Wallace in 1876 divided the land into six zoogeographic regions, still widely used: Palearctic, Nearctic, Neotropical (Neotropic), Ethiopian (Afrotropical), Oriental (Indomalayan) and Australian. Newer schemes, such as the one by Udvardy (1975), recognise eight biogeographic realms: Nearctic, Palearctic, Afrotropical, Indomalayan, Oceanian, Australian, Antarctic and Neotropical, further split into biomes and provinces. Biomes are large communities shaped by climate, such as tropical rainforest, savanna, desert, temperate forest, taiga, tundra and grassland. Wallace's Line separates the Oriental and Australian regions, and the realms are the basis for conservation planning and the WWF Global 200 ecoregions.
5 min read · UPSC Prelims · Environment & Ecology · Biodiversity Basics and Classification
At a Glance
- Wallace regions Six, 1876
- Udvardy realms Eight, 1975
- Indian realm Indomalayan
- Divide line Wallace’s Line
- Biome driver Climate
- Exam link UPSC Prelims, Environment & Ecology: Biodiversity Basics and Classification
Where Does It Fit?
This topic follows the patterns of biodiversity. It maps the world’s life regions, which is the base for the Indian classification and for hotspots and ecoregions. Previous topic: Patterns of Biodiversity. Next topic: Bio-Geographical Classification of India.
What Are the Major Biogeographic Realms of the World?
| Realm | Area and typical fauna |
|---|---|
| Nearctic | North America and Greenland. Bison, pronghorn, grizzly bear, bald eagle |
| Palearctic | Europe, North Africa and most of Asia north of the Himalaya. Largest realm. Brown bear, wolf, snow leopard, red panda in parts |
| Neotropical | Central and South America and the Caribbean. Jaguar, sloth, anteater, llama, toucans, piranha. Richest in birds |
| Afrotropical (Ethiopian) | Sub-Saharan Africa and Madagascar. Elephants, giraffe, gorilla, lemurs in Madagascar |
| Indomalayan (Oriental) | South and South-East Asia. Tiger, Asian elephant, rhino, gibbon, orangutan |
| Australasian (Australian) | Australia, New Guinea, Tasmania, New Zealand. Marsupials, monotremes, kangaroo, koala, platypus |
| Oceanian and Antarctic | Pacific islands and Antarctica. Penguins, seals, few land species |
What Are Biomes and How Do Realms Differ From Them?
- Biome: a large community type defined by climate and dominant vegetation, found in more than one realm
- Realm versus biome: realms depend on evolutionary history and geography, biomes on climate and form of vegetation
- Tropical rainforest: warm and wet, highest diversity
- Savanna: tropical grassland with scattered trees
- Desert: low rainfall, specialised plants and animals
- Temperate forest and grassland: moderate rainfall, seasonal
- Taiga (boreal forest): northern coniferous forest
- Tundra: treeless, permafrost
What Else Should You Remember?
- Alfred Russel Wallace: proposed the zoogeographical regions in The Geographical Distribution of Animals (1876)
- Wallace’s Line: a faunal boundary between Bali and Lombok, separating Asian and Australian fauna
- Weber’s Line: another line placing the balance of Asian and Australian fauna further east
- Wallacea: the zone between the lines, rich in endemics
- Holarctic: Nearctic and Palearctic together
- Gondwana: ancient southern landmass explaining links across southern continents
- Continental drift: explains why marsupials are in Australia and South America
- Endemism: Madagascar has high endemism with lemurs
- Island realms: Hawaii and Galapagos show unique evolution
- Darwin’s finches: show adaptive radiation on the Galapagos
- Convergent evolution: similar forms evolving in different realms, such as placental and marsupial wolves
- Ecozone: another name for realm
- Global 200: WWF’s list of priority ecoregions
- Terrestrial ecoregions: about 800 defined by WWF
- Marine realms: Marine ecoregions of the world divide coasts into realms
- Link to previous: see Patterns of Biodiversity
- Link to next: see Bio-Geographical Classification of India
- Link to ecoregions: see Eco-Regions
- Caution: names differ by author: Oriental equals Indomalayan, Ethiopian equals Afrotropical, Australian equals Australasian
- India’s position: India mainly in the Indomalayan realm with the Himalaya touching the Palearctic
- Ruling of continents: the Himalaya act as a barrier between the Palearctic and Indomalayan realms
- Biogeography: the science of distribution of life
- Vicariance: splitting of ranges by barriers such as rising mountains
- Dispersal: spread of species across barriers
- Exam hint: learn the six Wallace regions with one animal each, and note that India sits in the Indomalayan realm
- Nearctic features: its tundra, prairie and coniferous forests are shared with the Palearctic in the far north
- Neotropical birds: hummingbirds occur only in the Americas, and the region has more bird species than any other
- Afrotropical savanna: the Serengeti supports the largest migrations of large mammals on land
- Madagascar: separated from Africa about 88 million years ago, it holds lemurs, fossas and chameleons found nowhere else
- Indomalayan hotspots: the Western Ghats, Indo-Burma and Sundaland are biodiversity hotspots in this realm
- Australasian monotremes: the platypus and echidna lay eggs, a trait of the oldest mammal lineage
- Antarctic realm: tiny land fauna of insects and mites, but rich seas with krill, seals, whales and penguins
- Oceanian realm: scattered island groups with low diversity but many unique island species
- Palearctic corridor: Siberian species such as the Siberian crane migrate to Indian wetlands in winter
- Biogeographic regions and climate change: ranges are shifting poleward and uphill, which may blur realm boundaries over time
Why Does It Matter for the Exam?
- Regions: six or eight realms
- Line: Wallace’s Line
- India: Indomalayan
- Current affairs link: ecoregion conservation plans
- Common errors: confusing realms with biomes or placing marsupials in Africa
As an analytical point, realms reflect long evolutionary history and drifting continents, so unique species are concentrated in isolated realms such as Australasia and Madagascar. Conservation planning therefore uses realms and ecoregions to decide where to protect.
Why Is This Topic Important?
- Basis Species distribution
- Realms Six or eight
- India Indomalayan
What Came Next?
The next topic covers the bio-geographical classification of India. Next topic: Bio-Geographical Classification of India.
Key People and Terms
- Realm Biogeographic region
- Biome Climate-based community
- Wallacea Zone between the two lines
- Holarctic Nearctic plus Palearctic
- Vicariance Splitting by barrier
- Ecozone Alternative name for realm
Exam Corner
Points to Remember
- Wallace gave six regions in 1876.
- India is in the Indomalayan realm.
- Marsupials: Australasia.
- Largest realm: Palearctic.
- Biomes depend on climate.
Do Not Confuse With
- Realm and biome History-based region versus climate-based community
- Oriental and Indomalayan Same realm, different names
- Wallace’s and Weber’s Line Western versus eastern faunal boundaries
Memory Hook
Nearctic, Palearctic, Neotropic, Afrotropic, Indomalayan, Australian: six rooms in Wallace’s house.
Mains Angle
Questions ask for realm names and fauna. These points help.
- Realms Names
- Basis History
- Use Planning
A Question You May Face
An original practice question, not a past paper question.
“Describe the biogeographic realms of the world and explain the basis of their classification.”
How to Answer
- Basis Distribution.
- Realms Six or eight.
- Biomes Climate.
- Use Planning.
GS Relevance
Frequently Asked Questions
What are the biogeographic realms of the world?
Biogeographic realms are large regions of the world with distinct plant and animal life. Wallace described six: Palearctic, Nearctic, Neotropical, Ethiopian, Oriental and Australian. Modern schemes name eight realms by adding the Oceanian and Antarctic realms and use the names Afrotropical, Indomalayan and Australasian.
What is Wallace's Line?
Wallace's Line is an imaginary boundary in Indonesia, running between Bali and Lombok and between Borneo and Sulawesi, which separates the Asian fauna to the west from the Australian fauna to the east. It was identified by Alfred Russel Wallace in the nineteenth century and is a classic example of a biogeographic barrier.
In which biogeographic realm does India lie?
India mainly lies in the Indomalayan, also called Oriental, realm, which covers South and South-East Asia. The northern Himalayan and trans-Himalayan areas are influenced by the Palearctic realm, so they share species such as snow leopard and Tibetan species with Central Asia.
What is the difference between a realm and a biome?
A realm is a large geographic region defined by the evolutionary history and distribution of species, while a biome is a major type of ecological community defined by climate and dominant vegetation, such as desert or rainforest. The same biome, for instance tropical forest, occurs in several different realms.
Which animals are typical of the Australasian realm?
The Australasian realm is known for marsupials such as the kangaroo, koala and wombat, for egg-laying mammals like the platypus and echidna, and for birds like the emu and cassowary. Its long isolation has produced many endemic species that are found nowhere else.
PYQ Practice — Statement Analysis
1 Alfred Russel Wallace proposed six zoogeographic regions.
In 1876.
2 India lies mainly in the Neotropical realm.
In the Indomalayan realm.
3 Marsupials are characteristic of the Australasian realm.
Due to long isolation.
4 Wallace's Line separates African and Asian fauna.
It separates Asian and Australian fauna.
Past Mains Questions on This Topic
This topic comes under Biodiversity Basics and Classification. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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