On these encounter tables, you generate the monster type (animal, giant, humanoid, etc) and then roll for the specific monster. Why? Reason one is that it can accommodate more than 100 monsters per climate and terrain type.
Also, if a druid/ranger casts animal companion or sorcerer/wizards summons familiar, should you get a toad in a desert? Of course not. These tables neaten things up for you if you wish to limit the possibilities by climate and terrain.