Or are you referring to a self-perpetuating colony, where a few fry survive to reproduce, but they are the vast minority?

From the Immediate Help Section, you may have read the subsections on Breeding and Fry Diet and Safety. Basically provide less of the shelter and structure within a tank and more fry will be consumed by tank mates. A rough equilibrium can be achieved this way, even in a guppy only aquarium, but the numbers will still be awfully high for the growing guppies to be healthy long term. (When I was in Junior High, one pregnant female and her offspring ran that planted 10-gallon tank to over 230guppies of all sizes within a year.)

In this system, there will be a balance between older and younger guppies. On occasion there will sometimes be several adults, but few fry. As the adults die off of old age, the proportion of surviving fry greatly increases. Thank of how many fry would equal the weight of one big female.

You may find that a few other fish, which are harmless to adult guppies, which will take the fry, so there is not a disasterous population crash via an epidemic (nature's solution to over population). Dwarf gouramis, zebra danios, small tetras and fish of that sort will do the job pretty effectively if there is not a lot of shelter for the fry.

That sounds tough, but think of how many fry a pair has. Then consider that they only need to provide one breeding pair, on average, or one breeding pair after predation, for their species to continue.