optimum population
英[ˈɔptiməm ˌpɔpjuˈleiʃən]美[ˈɑptəməm ˌpɑpjəˈleʃən]
The optimum population is the size of a population that is the best out of several outcomes. There are, however, various opinions on what "optimal" means in this usage, resulting in various end-targets for it, but estimations usually take ecological sustainability and carrying capacity more or less into account.