Zoogeographic Regions and the Evolution of Biogeographic Realms
The distribution of animal species across the globe is not random; it is governed by geological history, climate, and physical barriers. To study these patterns, scientists use zoogeographic regions (also known as faunal regions), which are large-scale divisions of the Earth's surface based on the distribution of terrestrial animals. These regions are often further subdivided into provinces, territories, and districts, and in some classification systems, they are grouped into broader categories such as Empires and Domains.
In modern science, there is a growing trend to unify these zoological divisions with botanical floristic kingdoms, referring to them collectively as biogeographic realms.
Key Facts
- Foundational Work: Philip Sclater (1858) and Alfred Wallace (1876) established the primary zoogeographic regions still recognized today.
- Core Regions: The world is primarily divided into the Palaearctic, Afrotropic (formerly Aethiopian), Indomalayan (formerly India/Oriental), Australasian, Nearctic, and Neotropical regions.
- Marine Division: While terrestrial regionalization was established early, marine regionalization began later with the work of Ortmann in 1896.
- Classification Hierarchy: The system typically moves from broad realms down to specific districts.
The History of Regionalization
The effort to categorize the animal kingdom's geography saw various attempts throughout the 19th century. Early proposals varied wildly in scale: Schmarda (1853) suggested 21 regions, while Woodward proposed a complex system of 27 terrestrial and 18 marine regions. Other scholars, such as Murray (1866), Blyth (1871), Allen (1871), Heilprin (1871), Newton (1893), and Gadow (1893), proposed systems ranging from 4 to 8 regions.
The most enduring frameworks were developed by Philip Sclater and Alfred Wallace. Sclater's 1857 classification divided the world into the Creatio Palaeogeana (Palaearctic, Aethiopica, Indica, and Australiana) and the Creatio Neogeana (Nearctica and Neotropica).
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The Wallace and Sclater Legacy
Alfred Wallace refined these concepts in 1876, cementing the six-region model that serves as the basis for modern biogeography: the Palaearctic, Ethiopian, Oriental, Australian, Neotropical, and Nearctic regions.
Comparative Classification Schemes
Over time, different scientists grouped these regions based on different criteria, such as geological connectivity or climatic barriers.
Huxley's Groupings (1868)
Thomas Huxley organized regions into two primary groups: Arctogea (comprising the Nearctic, Palaearctic, Ethiopian, and Indian provinces) and Notogea (comprising the Austro-Columbia/Neotropical and Australasia provinces).
Trouessart's Expansion (1890)
Trouessart expanded the list to eight regions by specifically adding the Arctic and Antarctic regions to the existing six.
Darlington's Modern Analysis (1957)
Philip Darlington provided two distinct ways of viewing these regions. His first scheme grouped them into three realms: Megagea (Arctogea), Neogea, and Notogea. His second scheme categorized regions by the nature of their boundaries:
- Climate-limited regions: Palearctic and Nearctic.
- Old World tropics: Oriental and Ethiopian.
- Barrier-limited regions: Neotropical and Australian.
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Summary of Major Zoogeographic Frameworks
| Scientist (Year) | Primary Division/Grouping | Key Regions/Provinces |
|---|---|---|
| Sclater (1857) | Palaeogeana & Neogeana | Palaearctic, Aethiopica, Indica, Australiana, Nearctica, Neotropica |
| Huxley (1868) | Arctogea & Notogea | Nearctic, Palaearctic, Ethiopian, Indian, Austro-Columbia, Australasia |
| Wallace (1876) | Six Main Regions | Palaearctic, Ethiopian, Oriental, Australian, Neotropical, Nearctic |
| Trouessart (1890) | Eight Regions | Added Arctic and Antarctic to the six main regions |
| Darlington (1957) | Climate vs. Barrier Limited | Palearctic, Nearctic, Oriental, Ethiopian, Neotropical, Australian |
Frequently Asked Questions
What is the difference between a zoogeographic region and a biogeographic realm?
A zoogeographic region specifically focuses on the distribution of animals (fauna). A biogeographic realm is a more modern, inclusive term that combines both zoogeographic regions and botanical floristic kingdoms into a single classification system.
Who are the most influential figures in defining these regions?
Philip Sclater and Alfred Wallace are the most influential, as their 19th-century work established the six primary regions that remain the foundation of the field today.
What are 'barrier-limited' regions?
As defined by Darlington, barrier-limited regions are those whose unique biological makeup is primarily due to physical geographic isolation (such as oceans or mountains) rather than climate, with the Neotropical and Australian regions being the primary examples.
How has the naming of these regions changed over time?
Some names have evolved to be more descriptive of their geography; for example, the Aethiopian region is now commonly referred to as the Afrotropic region, and the Indian region is known as the Indomalayan region.