Population dynamics and management of Sus scrofa in western Switzerland: a statistical modelling approach

Abstract

In Western Switzerland as in other parts of Europe, the high densities of Sus scrofa have serious economic consequences for agriculture. In order to improve management actions and reduce impacts, we have undertaken a time series analysis on factors that may explain the increasing abundance of wild boars and have made stochastic simulations of population dynamics to assess the impact of management by hunting. Over a 32 years period, we show that the expansion of maize cultures explains 49.7% of the variance in the numbers of wild boars annually shot and is thus one of the main factors controlling population growth. Since the amounts of boars taken by hunting can be shown to be proportional to boar populations, we use the data furnished by hunters to calculate survival rates and fecundities for three age classes (0-1 year, 1-2 years, > 2 years) and simulate population dynamics using the RAMAS/age stochastic model for age structured populations. Density dependence parameters are also estimated from hunting data. The stochastic model produces fairly realistic predictions and simulations can be used to compare harvesting strategies. The statistical modelling approach presented in this paper is limited by the quality of parameter estimation, and, in the case of the stochastic population model, by its strong sensitivity to variations in density dependence parameters. However, qualitative predictions and risk assessments can be made, providing averyuseful tool for the improvement of Wild boar management.