WALLACE LINE

• Alfred Wallace (19th century) observed significant species differences between Asia and Australia.
• This observation led to the identification of the Wallace Line, a critical biogeographical boundary.

Wallace Line

• An imaginary boundary separating the distinct faunal regions of Asia and Australia.
• Biogeographical Significance: Marks a major division with stark differences in species composition on either side.

Geographical Location:

• Runs through the Makassar Strait (between east coast of Borneo and west coast of Sulawesi).
• Extends between Bali and Lombok, separating the Sunda (Asian) and Sahul (Australian) continental shelves.

Species Distribution:

• West of the Wallace Line (Bali, Borneo, Java, Mainland Asia):
  • Fauna includes monkeys, apes, rhinos, squirrels, tigers, hornbills—typical of the Asian ecosystem.
• East of the Wallace Line (Lombok, Sulawesi, Timor, Australia):
  • Fauna includes tree kangaroos, cockatoos, honeyeaters—characteristic of the Australian ecosystem.

Wallacea Region:

• Lies between the Wallace Line and the Weber Line (another faunal boundary to the east).
• Includes islands like Sulawesi, Flores, Lombok, Timor.
• Unique Species:
  • Komodo dragon, babirusa, giant bees (isolated Wallacean islands with lower biodiversity but unique species).
  • Sulawesi hosts both Asian species (e.g., tarsiers, anoas) and Australian marsupials (e.g., dwarf cuscus).

Reason for Formation:

• Continental Drift:
  • ~85 million years ago, Australia separated from Antarctica, drifting northward, isolating species and promoting independent evolution.
• Deep Oceanic Barriers:
  • Deep waters like the Makassar Strait remained submerged during ice ages, acting as barriers to species migration.
• Geological Climate Change:
  • Different climates in Asia and Australia made it difficult for species to migrate across the line, reinforcing distinct ecosystems.