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How can scientists use endemic species to draw the boundaries of biogeographic regions?

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World map using color coding to show the distribution of major floral kingdoms, subkingdoms, and regions. Key floral kingdoms include Boreal (green), Neotropical (pink), Paleotropical (yellow), South African or Capensic (purple), Australian (orange), and Antarctic (blue). Boundaries for subkingdoms, regions, and divisions are marked with different colored lines, and major regions such as Indoafrican, North American, and Malesian are labeled across continents. — biogeographic region Floral kingdoms, subkingdoms, and major regions of the world.

Scientists use endemic species—taxa whose distribution is confined to a specific area—as a foundational tool for defining the boundaries of biogeographic regions.

The process involves mapping the geographic distributions of numerous taxa. A boundary line for a biogeographic region is typically drawn where the outer limits of many of these species coincide. Major regions, such as kingdoms and realms, are identified by their high concentration of endemic species or by the fact that they share the fewest taxa with other regions. As these regions are further divided into smaller subdivisions, the number of unique endemic taxa within those areas decreases.

While this method has been historically significant, it is sometimes criticized for assuming that species ranges are stable over time. Consequently, modern approaches may also incorporate quantitative methods, such as calculating the degree of biotic similarity between regions using Jaccard’s coefficient, to refine these boundaries.