India's biogeographic classification is a division of the country based on biogeographic characteristics. A biogeographic realm, also known as an ecozone, is the broadest biogeographic division of the Earth's land surface based on terrestrial organism distribution patterns. They are further subdivided into bioregions and ecoregions. Biogeographic realms are large spatial regions in which ecosystems have a broadly similar biological evolutionary history. Eight terrestrial biogeographic realms are commonly recognised, roughly corresponding to continents. In this article, we will discuss Realms - Indian Biodiversity Diverse Landscape which will be helpful for UPSC exam preparation.

What are Realms?

• Biogeographic realms are large geographic areas where ecosystems share a broadly similar biota.
• A realm is a continent or subcontinent-sized area with unifying geographical and fauna and flora features.
• The Indian region is divided into two realms:
• The Himalayan region is represented by Palearctic Realm;
• The rest of the subcontinent is represented by Malayan Realm.
• Palearctic Realm - The Palearctic, also known as the Palaearctic, is the largest of the Earth's eight biogeographic realms. It encompasses all of Eurasia north of the Himalayan foothills, as well as North Africa.
• The realm is divided into several bioregions: the Mediterranean Basin, the Sahara and Arabian Deserts, as well as Western, Central, and East Asia.
• There are numerous rivers and lakes in the Palaearctic realm, forming several freshwater ecoregions.
• The term "Palearctic" was coined in the nineteenth century and is still used as the basis for zoogeographic classification today.
• Malayan Realm - According to the Bioregions 2020 framework, Indomalaya is one of the world's eight major biogeographical realms and has three subrealms: the Indian Subcontinent, Southeast Asian Forests, and Malaysia and Western Indonesia, with a total of 18 bioregions.
• With its dense rainforests, this is one of the world's most important areas for biodiversity, containing one-fifth of all plant, animal, and marine species.
• The region is home to three mega-diverse countries: Indonesia, Malaysia, and the Philippines, which are home to four of the world's 25 biodiversity hotspots.
• The western Indian Subcontinent is capped by the long, curving Himalayan mountain range and includes dry forests, scrublands, and deserts up to the Arakan mountain range.
• The Southeast Asia subrealm, dominated by subtropical evergreen forests, extends northward from the Indochinese Peninsula to the edge of China's Yunnan-Guizhou plateau.
• The South China Sea and the Philippines are also included in this subrealm.
• Further south, the Malaysia & West Indonesia subrealm, which contains hundreds of islands, is dominated by moist broadleaf forests and coastal mangroves.

Biogeographic Realms

• At the broadest level, referred to as the realm in Udvardy (1975), all of India falls within the Indomalayan realm, with the exception of the high Himalayas, which fall within the Palearctic realm.
• The majority of India is part of the Indomalayan realm's "Indian Subcontinent" bioregion, which includes the majority of India, Pakistan, Bangladesh, Nepal, Bhutan, and Sri Lanka.
• The bioregion is bounded on the northwest, north, and northeast by the Hindu Kush, Karakoram, Himalaya, and Patkai ranges; these ranges were formed by the collision of the northward-drifting Indian subcontinent with Asia 45 million years ago.
• The Hindu Kush, Karakoram, and Himalaya ranges form a major biogeographic barrier between the Indian subcontinent's subtropical and tropical flora and fauna and the temperate-climate Palearctic realm.
• The Nicobar Islands, on the other hand, are part of the Indo-Malayan realm's "Sundaland" bioregion.
• The Himalayas form the southern limit of the Palearctic in South Asia, and it is here that Palearctic temperate forests transition to Indomalayan subtropical and tropical forests, resulting in a rich and diverse mix of plant and animal species.

Realms of the World

Eight terrestrial biogeographic realms are commonly recognised around the world. They are as follows:

• Nearctic Realm
• Palearctic Realm
• Afrotropical Realm
• Indomalayan Realm
• Oceania Realm
• Australian Realm
• Antarctic Realm
• Neotropical Realm

Ecoregions in India

• An ecoregion (ecological region) or ecozone (ecological zone) is a smaller ecological and geographically defined area than a bioregion, which in turn is smaller than a biogeographic realm.
• Ecoregions of the world were first defined and mapped in 2001, spanning all land area (terrestrial) of the planet, and were later revised in 2017.
• Later, global freshwater and marine ecoregions were identified.
• India has 46 terrestrial ecoregions, 14 freshwater ecoregions, and 6 marine ecoregions.

Terrestrial Ecoregions

• The world's terrestrial ecoregions include 46 ecoregions that are entirely or partially located within India's borders. These ecoregions are classified as Indomalayan and Palearctic biogeographic regions.
• They are also classified into ten biomes:
  • Deserts and Xeric Shrublands
  • Flooded Grasslands and Savannas
  • Mangroves, Montane Grasslands and Shrublands
  • Temperate Broadleaf and Mixed Forests
  • Temperate Conifer Forests
  • Tropical and Subtropical Coniferous Forests
  • Tropical and Subtropical Dry Broadleaf Forests
  • Tropical and Subtropical Grasslands
  • Savannas and Shrublands and Tropical
  • Subtropical Moist Broadleaf Forests
• Rock and Ice is not classified as a biome or biogeographic realm.

Freshwater Ecoregions

• The world's freshwater ecoregions have been identified as a large area encompassing one or more freshwater systems with a distinct assemblage of natural freshwater communities and species.
• Freshwater species, dynamics, and environmental conditions within a given ecoregion are more similar to one another than to those of neighbouring ecoregions, forming a conservation unit.
• India has 14 freshwater ecoregions:
  • Upper Indus
  • Indus Himalayan Foothills
  • Lower and Middle Indus
  • Ganges Himalayan Foothills
  • Middle Brahmaputra
  • Chin Hills-Arakan Coast
  • Plain and the Ganges Delta
  • Narmada–Tapti
  • Northern Deccan Plateau
  • Southern Deccan Plateau
  • Southeastern Ghats
  • Western Ghats
  • Andaman Islands
  • Nicobar Islands

Marine Ecoregions

• Marine ecoregions have been described for the world's oceans and seas.
• India's seas are located in the Western Indo-Pacific marine domain. This includes the four provinces listed below, as well as six marine ecoregions.
• West and South Indian Shelf Province
  • Western India
  • South India and Sri Lanka
• Central Indian Ocean Islands Province
  • Maldives
• Bay of Bengal province
  • Eastern India
  • Northern Bay of Bengal
• Andaman Province
  • Andaman and Nicobar Islands

Conclusion

Assessing biodiversity at the biogeographic realm level is important because the realms exhibit significant variation in the extent of change. They face different drivers of change, and there may be differences in the options for mitigating or managing the drivers. Biogeographic regions are geographical areas defined by the species found within them, which provides ecologists and natural resource managers with invaluable information for understanding large-scale processes that affect species and ecosystems.