Wallace Line

• 05 Mar 2025

Source: TH 

Why in News? 

In the 19^th century, Alfred Wallace observed a change in species composition between Asia and Australia. This difference in species composition later developed as the Wallace Line. 

What is the Wallace Line? 

• About: The Wallace Line is an imaginary boundary separating the distinct faunal regions of Asia and Australia.  
  • It marks a major biogeographical division with stark species differences on either side of the line. 
• Geographical Location: It runs through the Makassar Strait, which lies between the east coast of Borneo and the western coast of Sulawesi.  
  • It extends between Bali and Lombok, separating the Sunda and Sahul continental shelves. 

 

• Species Distribution: West of the Wallace Line (Bali, Borneo, Java, and mainland Asia), fauna consists of monkeys, apes, rhinos, squirrels, tigers, and hornbills, which are characteristic of the Asian ecosystem. 
  • East of the Wallace Line (Lombok, Sulawesi, Timor, and Australia), fauna includes tree kangaroos, cockatoos, and honeyeaters, linked to the Australian ecosystem. 
• Wallacea Region: The region between the Wallace Line and the Weber Line (another faunal boundary to the east) is known as Wallacea and includes islands like Sulawesi, Flores, Lombok, and Timor. 
  • Isolated Wallacean islands have lower biodiversity than nearby continents but host unique species like the Komodo dragon, babirusa, and giant bees. 
  • Sulawesi is home to both Asian species like tarsiers and anoas, and Australian marsupials like the dwarf cuscus. 
• Reason for Formation: 
  • Continental Drift: About 85 million years ago, Australia separated from Antarctica and drifted northward, isolating species and driving independent evolution. 
  • Deep Oceanic Barriers: It aligns with deep waters like the Makassar Strait, which remained submerged even during ice ages, limiting species movement between Asia and Australia. 
  • Geological Climate Change: Asian and Australian species, suited to their respective climate, struggled to migrate either side of the line.

UPSC Civil Services Examination, Previous Year Question (PYQ) 

Prelims 

Q. Which one of the following pairs of islands is separated from each other by the ‘Ten Degree Channel’? (2014)

(a) Andaman and Nicobar 

(b) Nicobar and Sumatra 

(c) Maldives and Lakshadweep 

(d) Sumatra and Java 

Ans: (a)

Q. Consider the following statements: (2010) 

1. Biodiversity hotspots are located only in tropical regions. 
2. India has four biodiversity hotspots i.e., Eastern Himalayas, Western Himalayas, Western Ghats and Andaman and Nicobar Islands. 

Which of the statements given above is/are correct? 

(a) 1 only  

(b) 2 only 

(c) Both 1 and 2  

(d) Neither 1 nor 2 

 Ans: (d)