Individual-based models for the growth dynamics of a population have to formalize mathematically the basic processes defining the life history of an individual of the population. In particular, the process of development, from birth to death, of a generic individual. The model equations for this process are stochastic equations and describe the time evolution of the status of an individual, in terms of a physiological age.
In this paper we are addressed to the formulation of development models, when regression effects on the status of an individual are forbidden; this is the case when the physiological age is defined in terms of an abstract indicator, i.e. the percentage of development. Different stochastic models of the development process are presented, and their responses are compared. Their behaviours are analyzed by varying the stochasticity level, which takes into account the degree of intraspecific variability. A multi-stage system, representing a copepod population, is used to illustrate the results of the analysis, by means of numerical simulations.
Furthermore, some computational aspects, related to the implementation of an individual-based model, are illustrated.

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