Final answer:
The "Wallace line" is an imaginary line that separates the Asian realm and the Austral realm. It marks a division between distinct groups of species.
Step-by-step explanation:
The "Wallace line" is an imaginary line just north of Australia that separates the Asian realm and the Austral realm. It was developed by Alfred Russel Wallace to explain the differences in biodiversity between these two regions. The Wallace line is significant because it marks a division between distinct groups of species. The species found on the Asian side of the line are more closely related to species in Asia, while the species on the Austral side are more unique to that region.