Why are cold-adapted species on tropical mountains more isolated than those on temperate mountains?

Cold-adapted species on tropical mountains are more isolated than those on temperate mountains primarily because of the surrounding environment. In temperate regions, historical glacial intervals allowed cold-adapted biota to migrate across vast areas as ice sheets expanded and retreated, facilitating connectivity between mountain ranges and high-latitude regions.1

In contrast, tropical mountains are surrounded by vast, warm tropical rainforests or lowland forestlands that act as a formidable barrier to the migration of cold-adapted species. Because these organisms cannot traverse the hot lowlands, they remain trapped on high-altitude "islands" of cool climate, leading to more complete isolation from other cold environments. While some mobile species, such as birds, have managed to colonize these equatorial peaks, the lack of overland movement for most plants and animals results in distinct, often rapidly evolved species on separate mountain summits, contributing to high levels of biodiversity within these isolated ecosystems.1