Essay on Varying Patterns of Speciation

2129 Words 9 Pages
Varying Patterns of Speciation

Wallace’s line, located in the Malay-Archipelago, is one of the best known and most studied boundaries of zoogeography in the world. It is a transition zone between the islands of Borneo and Sulawesi and the islands of Bali and Lombork, which marks both the convergence and division of the diverse flora and fauna found in the Asian (Borneo, The Philippines, and Western Indonesia), and the Australian regions (Sulawesi, Eastern Indonesia, Australia, and New Guinea) (Schulte 2003). The hypothetical line was first proposed by Alfred Russel Wallace in 1858 after observing many morphological differences of various bird species in the Asian and Australian regions (Raven 1935). In the past, to confirm the
…show more content…
Around 140 million years ago India separated from the still connected South America-African and Antarctica-Australian landmasses and drifted northward until it collided with Eurasia (Europe and Asia). This collision created a continental block which caused a separation of the Antarctica-Australia landmass and caused the individual landmasses to shift in opposite directions (Whitmore 1981). This separation formed an underwater ocean ridge, which caused Australia to drift northwestward. Around 15 million years ago, Australia converged with Asia, uniting the diverse flora and fauna of both regions (Schulte 2003; Whitmore 1981). It was then the continuous separation of these two landmasses that has dynamically shaped the present-day distribution of unique ecosystems and species found on the Asian and Australian continents, as well as on the islands in the Malay-Archipelago.

When Wallace drew his hypothetical line to define the boundary between Asian and Australian zoology, he had an incomplete understanding of continental drift and plate tectonics. He only used morphological observations of cockatoos found on Lombork and Bali, and of parrots found on Borneo and Sulawesi, to support the placement of his line
Open Document