mountain passes are higher in the tropics—divergent climate tolerances play crucial roles in how species evolve /

In tropical climes,animals and plants aren't adapted to surviving freezing temperatures - and why would they be? It's never all that cold near the Equator, even at altitude. But in places like the Rocky Mountains, and where temperatures can climb into the 100s and dip below freezing,species are hardier and more equipped to deal with such fluctuations.

Source: phys.org