Structure of the VORTEX simulation model for population viability analysis

The structure of the VORTEX computer simulation model for population viability analysis is outlined. The program flow is described here in order to provide a detailed specification of the structure of a widely used population viability analysis model. VORTEX is an individual-based simulation program that models the effects of mean demographic rates, demographic stochasticity, environmental variation in demographic rates, catastrophes, inbreeding depression, harvest and supplementation, and metapop ulation structure on the viability of wildlife populations. The model facilitates analysis of density-dependent reproduction and changing habitat availability, and most demo graphic rates can optionally be specified as flexible functions of density, time, popula tion gene diversity, inbreeding, age, and sex. VORTEX projects changes in population size, age and sex structure, and genetic variation, as well as estimating probabilities and times to extinction and recolonization.