Modelling the Dynamics and Management of Ibex Populations in Switzerland

Abstract The IBEX (Capra ibex) was reintroduced in Switzerland in 1906, and then given a protected-species status. Since then its numbers have grown rapidly, and are now becoming excessive, as attested by heavy damages to the environment in certain areas, competition with the CHAMOIS (Rupicapra rupicapra) and the appearance of epidemics. For this reason, some culling was authorised in the 1980s, but this has been conducted purely on the basis of empirical data. Our objective is to develop culling strategies on more rational grounds. Due to its biological peculiarities and protected status, the Ibex seems particularly suitable for this approach, especially with respect to the quality of statistical data available. How many animals to cull, and of which sex, age or populations ? To answer such questions we are developing a computer model designed to test various options. The preliminary version (Sim-Ibex 1.1) estimates, on the basis of the statistics available for each colony, the dependence of the fecundity and survival on the age and density in each population, as well as the magnitude of environmental stochasticity. On this basis, it then provides simulations of local population dynamics, and finally proposes and tests locally-adapted culling strategies. This version is user-friendly enough to be used directly by fauna managers. The next steps in our work will consist of refining the parameters of the model and extending it in order to include the effects of the spatial structure of colonies and migrations between them. Finally we shall examine the possibilities of extending the software to other ungulate species.