Accueil du site
Doctorat
Australie
1995
The dynamics of feral pig populations in the semi-arid rangelands of Eastern Australia
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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