Science Now has a short article about Pompeii worms, which grow right near hot vents at temperatures up to 80 Celsius. The worms live inside little tubes and appear to keep cool by sucking sea water in via a kind of piston action. Colonies of tube worms then serve in effect as a heat-exchange device , cooling the magma heated waters, which in turn may make things a bit nicer for neighboring bacteria. So, inch by inch as you get away from the vent, the inhabitants change.
What continually amazes me about extremophile communities are the very narrow growth zones, defined by steep gradients of pH, humidity, and/or temperature. You get just a millimeter out of your zone and you're history. Of course, humans can only really live up to few miles above sea level themselves, because of limitations on lung function. Compared to the earth's radius, that could be considered a narrow niche as well.