system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are deer suited to almost everywhere on the planet?

The biodiversity of the planet is amazing, everywhere you go there's millions of different species to discover.

Simultaneously, almost everywhere you go there's a deer population except for Africa and Australia.

How are deer this generalized that they can survive practically anywhere? How has this type of creature become so dominant in its niche almost planet-wide?

Edit: Apparently they are basically everywhere including Australia and Africa.
gpt
Bit of a correction, there are deer in Africa too!

In general this is probably because deer are fast, grazers, can defend themselves somewhat, and reproduce fairly quickly.

All of these things meant that deer, over time, were pushed to every continent either by predators or food scarcity and were able to make those travels to disconnected continents when they were still connected by land bridges.