Does anybody know a reliable mathematical expression of the population growth? I mean, starting with a known group (i.e. knowing sex ratio, age group, fertility ratio and natural mortality) is it possible to calculate the polpulation size in say, 10 years?
I tried with some example found on game management books, but did not succeed, as I was not able to find how to express the mechanism against overpopulation (e.g.: loss of fertility).

I have done this for years with northern spotted owls and feral hogs; two very different animals and expressions, typically calculating Sigma.

There are numerous models available depending on rigidity of your data, as well as the breadth of the data. You need the model to meet your data, don't push the data into an expression that might have inherent errors due to data.

See if this helps?

Brian Dennis, Patricia L. Munholland and J. Michael Scott. Ecological Monographs
Vol. 61, No. 2 (Jun., 1991), pp. 115-143