ALEX - A MODEL FOR THE VIABILITY ANALYSIS OF SPATIALLY STRUCTURED POPULATIONS

A new generic model for assessing the viability of spatially structure d populations, ALEX (Analysis of the Likelihood of EXtinction), is des cribed. Strengths and weaknesses of ALEX are discussed ALEX only model s one sex, ignores genetics, and is inadequate for modelling the dynam ics of very small populations. However ALEX contains four features tha t make it useful for assessing the merits of different management opti ons for populations that are distributed in a spatially complex landsc ape: (1) ALEX allows each patch to have different qualities including a habitat variable that may respond to catastrophes. In this way the d ynamics of species which prefer a particular successional stage of a h abitat can be modelled. (2) ALEX allows the user to specify a wide var iety of catastrophic processes that affect and may depend on populatio n size and/or the state of the habitat in a patch. (3) Sensitivity ana lysis is essential to the PVA process. ALEX allows automatic sensitivi ty analysis of most parameters. Although demographic stochasticity is modelled, ALEX can quickly simulate the dynamics of very large populat ions. (4) Modelling movement between patches by individuals is an impo rtant part of the dynamics of spatially structured populations. ALEX p ermits two types of movement by individuals. This allows the user to e xplore the importance of corridors, habitat selection, and mortality a ssociated with dispersal.