Earth Floor: Biomes. There are many different kinds of plants and animals on the Earth, but only certain kinds are naturally found at any particular place.
(We are not counting zoos here!) For example, cacti are found in the desert, polar bears are found in the Arctic, and elephants are found in central Africa and India. So, why don't people living in south Texas have to be on the lookout for snow leopards, or why don't kids in Minnesota have to worry about finding giant boa constrictors in their back yards? It is because these animals are not adapted to live in the average weather conditions found in Texas or Minnesota.
References.