system
Given the following post, respond as if you're commenting on Reddit:
human
Why are moose only found in northern parts of the world?

The kind of food they eat seems to be plentiful in warmer climates in the south. Why haven't they colonized lower latitudes?
gpt
Evolution generally favours larger, fewer (warm-blooded) animals in very cold climates. Consider polar bears, walrus, etc. While there is large fauna in other climates, it is much more diverse (you have both large and small animals, with smaller ones in greater quantity), which is not the case in colder climates.

The reasons for this come down to evolutionary advange. It's less about whether moose could survive (in the absence of competition) in warmer climates, and more on who *cannot* compete with the moose in cold climates (and would otherwise out-compete the moose for food). Cold climates give an advantage to a large, warm blooded animal (heat is easier to keep thanks to the square-cube law). Energy reserves can also be stored longer, and spent slower, relative to muscle expenditures (again, square-cube law), useful in the frigid climate where food is very scarce. 

This means that in the northern climates, smaller herbivores cannot compete with the moose due to hypothermia or insufficient food. Which means that the moose's advantages outweight its disadvantages (needs lots of food in *absolute* terms, less mobile, etc.) that it would face in warmer climates relative to other animals, with whom it would not be able to compete for food.