Models of growth with density regulation in more than one life stage

Discrete-time models of growth of populations with nonoverlapping generations and density regulation in two life stages are studied. It is assumed that there is no delay in the effects of density. Assigning exponential, linear, or hyperbolic functions to describe the dependence of preadult survival and fecundity on density, nine models are obtained. The dynamics of the model resulting from using the exponential function to describe the density dependence of both preadult survival and fecundity is analyzed: for large values of the intrinsic rate of increase there may exist up to three equilibrium population sizes, two stable. This indicates that a life history with two episodes of density regulation can give origin to alternative stable states. The models are fitted to recruitment data from growth experiments of Drosophila laboratory populations obtained with the Serial Transfer System Type 2 (Ayala et al., 1973. Theor. Pop. Biol. 4, 331-356) and collected by other authors. The results of the fittings suggest that this recruitment data can be adequately described with the models.