Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : The dynamics of feral pig populations in the semi-arid rangelands of Eastern Australia

Auteur : Choquenot, David

Université de soutenance : University of Sydney

Grade : Doctor of Philosophy PhD 1994

Résumé partiel
(1) A great deal of interest and some controversy has surrounded the role of food availability in the limitation and regulation of large herbivore populations. This study tested the applicability of two hypotheses used to understand and predict variation in the abundance of large herbivores, to populations of feral pigs inhabiting the semi-arid rangelands of inland Australia. The intrinsic food hypothesis proposes that the density of herbivores is regulated at or around some equilibrium (K) through density dependent variation in the rate pf change in their abundance (r), through the effect of per capita food availability on their demographic rates. The extrinsic food hypothesis, proposes that herbivores do not affect variation in the abundance of their food resources and hence are not regulated through the effects of density dependent variation in per capita food availability on r.
(2) The applicability of the two hypotheses to feral pig populations was tested using a manipulative experiment, in which the abundance of pigs on six sites in the rangelands was reduced to one of three levels (x2 replicates) annually, and the abundance of pigs and their primary food resource (non-improved pastures), was monitored quarterly over two and a half years. Depending on the tendency of the pig/pasture grazing system toward equilibrium, the intrinsic food hypothesis predicted either a negative or non-significant relationship between rate of change in pig abundance and pig density. Regardless of this tendency, the intrinsic food hypothesis also predicted a negative relationship between pasture availability and pig density and a positive relationship between rate of change in pig abundance and pasture availability. The extrinsic food hypothesis predicted non-significant relationships for both rate of change in pig abundance and pasture biomass with pig density, and a positive relationship between rate of change in pig abundance and pasture availability.
(3) Despite large fluctuations in both pig and pasture abundance over the course of the experiment, no significant relationship between pig density and either rate of change in pig abundance (measured as the annual exponential rate of increase (r) for each study site) or pasture biomass could be demonstrated. However, a strong positive relationship between pasture biomass lagged three months and r was detected. Collectively these results suggest · that pig populations in the rangelands conformed to the extrinsic food hypothesis, their abundance being limited but not regulated by food availability

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