What promotes persistence of a single population: an individual-based model

A family of models was analysed describing dynamics of single populations with non-overlapping generations and explicit resources: a model with all individuals being identical, the same model but with a constant and resource-dependent random mortality, and a model with individual variation due to competition for resources. The population made up of identical individuals cannot be regulated. It grows exponentially and then declines to zero. The population with a constant random mortality typically shows identical behaviour, only the extinction time of the population being longer. Less frequent in this case were declines to low numbers after the first maximum followed by exponential growth to the second maximum, and only then final extinction. The population with random resource-dependent mortality has an intermediate extinction time between that of the population without random mortality and with a constant mortality. Population can be regulated only in the model with individual variation. Persistence of such a population depends on the way in which individual hierarchy is established during resource partitioning and on the frequency of competition among individuals over their life cycle.