Hey Jeff,
I use .177 (800 - 900's FPS range) and .22 cal springers for my small game hunting and routinely take tough skinned squirrels within 40 yards. Shot placement of course is of key importance no matter what you're shooting. I try to keep my small game shots under 40 yards if I can. I also use my .22 cal springers for almost all my hunting, but the .177 guns get their chance to take game as well.
As for prairie dogs,,,,,, I can't speak about hunting them as the only prairie dogs I've ever seen were at the Bronx Zoo in New York City. I'm sure one of the other guys can give you advice about shooting those critters.
Jeff