Wallace's and Weber's Lines
Wallace's and Weber's Lines (see Figure 10.15) are hypothetical lines geographers have drawn to separate biogeographical realms. Some call these lines "faunal boundaries". The naturalist Alfred Russel Wallace created a line to separate the species of Asian and Austral origin between Borneo and Sulawesi and between Bali and Lombok.
Max Carl Wilhelm Weber, a biogeographer and zoologist, believed the boundary between the species was farther east, between Sulawesi and Buru, coming much closer to the island of New Guinea and the continent of Australia.
During the ice ages, colder global temperatures meant that glaciers could advance, and sea levels were lower. Consequently, animals were able to cross from one landmass to another across land bridges. However, the continental shelf may have been too deep for animals to cross in some locations. For example, we only find Marsupials on the Austral side because they were unable to cross to the Asian side.
Figure 10.15 Wallace's and Weber's Lines
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