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Why are endemic species especially common on islands and in mountain ranges?

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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.

Endemic species are particularly common on islands and in mountain ranges primarily due to geographic isolation. This isolation acts as a barrier that prevents populations from interbreeding with others, facilitating allopatric speciation.12

The Role of Isolation

Islands: Because they are removed from the mainland, islands often host unique species that have evolved in situ. The limited land area and physical separation promote adaptive radiation, where ancestral groups diversify into various specialized forms to fill available ecological niches.3
Mountain Ranges: Mountains function similarly to "islands" of specific climates surrounded by different, often warmer, environments. High peaks are frequently isolated from one another, allowing cold-adapted biota to evolve independently on separate summits.45

Evolutionary Drivers

When populations are separated by barriers like water or rugged terrain, they adapt to their unique local environments. Over time, these populations become so genetically distinct that they can no longer interbreed with their original lineages. This process often results in the rapid emergence of new species, contributing significantly to the high biodiversity found in these regions.245