Exactly what Funkadelic Jive Turkey said...this is something that annoys me about a lot of D&D based games. A lot of DMs throw the whole monster manual at you, as if all those creatures existed in the same world. But the monster manual is just a bunch of
ideas for creatures to include in a
setting. So if you play in an actual setting, you would rarely or never see most of those monsters. In fact, pretty much the only people who would ever see some of those would be adventurers, who make a habit of finding dangerous places, while your average farmer might hear a story now and then but would never see a dragon or unicorn or whatever.
DF handles this well, I think. The wilderness isn't that dangerous, most of the world is pretty safe. For the occasional lion or whatever, every town has some guards and militia. If you're an adventurer, then sure the world seems filled with danger because you're always going to the most dangerous ruins and caves, &c. The only people who travel are merchants, and they always bring a guard or three to protect them.
So, in short, each race survives pretty easily, it doesn't seem much more difficult than it is in real life. Probably the biggest threat to existence is war, particularly with goblins, but each race seems pretty well-equipped for that (except for elves, which I assume will get some means of defense in addition to their archers). As for other fantasy settings, some of that stuff really is ridiculous.