Population Estimation

Hello, new member here and I've been looking for a way to make a number cruncher for a (imaginary) colony of creatures for an RP I'm making.

I'm trying to figure out an approximate size of this colony based on several pieces of data I've got at hand, and I've been looking for a way to properly estimate just how big the thing is.

The simple of it is the creatures that inhabit this colony have a 7 month gestation period, and a 5 month 'down time' between gestations.

Once born, the creatures live 14 years before they're able to give birth themselves, and eventually die off somewhere around their 20s. The colonies usually size in the hundreds of adult members.

Ideally, having the formulas to be able to estimate the % of "toddlers" based on the number of adult members of the breed would be ideal, but I fear I've gone in over my head and attempted to pay too much attention to something that should've remained in the realm of fiction.


Omega Contributor
What is RP?

Probably many many questions need to be answered.

Are there a limited amount of resources, or do you assume there is no restriction (e.g., food, area, etc.)?

Can they be asexual?

Are they monogamous?

Is there an even number of males/females given to start with and within the offspring?

Is there any types of infant/child mortality to account for?

Are all pregnancies just singletons?

Are all people virile/fertile?

Side note, I have seen statements on rats and if unrestricted, they can have millions of progeny/decedents in a year.
RP = Role Play, D&D and stuff.

Resources are considered enough to sustain a population ranging 300 to 400 (of this critter).

They solely reproduce through parthenogenesis (they clone themselves, no sex/relationships involved).

Between birth and reaching adulthood around 20% will die off (estimated, this is a non-existent species after all).

Litters are usually of 2.

If they somehow live past their 20s they become sterile.

What I was looking for is to somehow estimate the % of the "infants" of a colony when knowing the number of adults in it.


Omega Contributor
So once the population hits 300-400 people, there will be no new infants until an adult dies? Does a 365 day calendar exist in this world, just kidding.
So... I'm guessing there's no easy way to calculating that without getting several more variables than what I've got at hand.

Considering unlimited resources... would it be easier to calculate the %s?


Omega Contributor
Well you can definitely calculate it, you just have to figure out the function and time frame. This is not my forte, I just wanted to reply.

So if you have 200 people, at baseline (T0), then at T+7 months you have 400 people, then at T19 your have 600 people, then at T31 you have 800 people..., then you include the new people and some descease, etc. Somebody should be able to write this function out. Say population = n * (n + 7 months) - n * .20 + ... something like this. Perhaps start by figuring out the first parts and build on it while waiting for more post.