In my 2.5 gallon I had about a hundred 0.75-1 cm RCS/PFRs plus 18 breeding adults. The oldest shrimp were 6 weeks old. And they were 1 cm. From what I understand, they should be a good bit larger. I moved 1 RCS (by accident, actually) to my Ebi, which is lightly stocked, and a week later it's over half an inch. So that goes to show how what you're asking about works.
I have since sold off about 35-40 of the shrimp. Still got lots more though!
Here's a slightly off topic question, but related to the whole breeding and baby shrimp and population topic: do products like mosura Eros make baby shrimp and juvies grow faster by causing them to molt more? Or does it only really work with adults.
It might. They are self limiting in that if you get to many disease, starvation, or decreased water quality will start reducing the numbers. The problem is though since you have a small closed enviroment this may happen in a catastrophic way that will wipe out the entire population. Even if it doesn't wipe out the entire population it would probably wipe out 80-90%+ before it stabalized. For example if you had 300 shrimp in a tank and the water quality started to deteriorate then a few might die. Their decomp would pollute the water more resulting in more deaths, and the cycle may continue till they are all dead or until you have 10 left that somehow survived and start to repopulate.
This doesn't happen in nature any more than it happens in a shrimp tank.
The animals will reproduce unchecked until they starve, die of disease, or are preyed upon. There's no natural governor that keeps population growth down to a certain speed beyond those things. Here we can add poor water quality to the list, but the shrimp will still happily reproduce out of control if given the opportunity. If the population doesn't crash due to one of these factors, eventually conditions will degrade until the survival rate of new shrimp equals the mortality rate of older shrimp and the population will stabilize.
Look at rabbits and mice in Australia, or human beings just about anywhere on the planet, or kudzu in the south of the US. If an organism can grow and reproduce, it will.