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Accueil du site → Doctorat → Australie → 2002 → Spatio-temporal interactions of mammalian herbivores in the arid zone

University of New South Wales (2002)

Spatio-temporal interactions of mammalian herbivores in the arid zone

Witte, Ingrid

Titre : Spatio-temporal interactions of mammalian herbivores in the arid zone

Auteur : Witte, Ingrid.

Université de soutenance : University of New South Wales

Grade : Doctor of Philosophy (Ph. D.), 2002.

The spatio-temporal interactions of four native herbivores (red, eastern and western grey kangaroos and euros) and three introduced herbivores (sheep, goats and rabbits) were investigated over three years at Fowlers Gap in the sheep rangelands of western New South Wales. These herbivores are subjected to a highly variable resource base, both in quantity and quality of forage, driven largely by rainfall with an annual coefficient of variation of 55%. The vegetation was subjected to seasonal, six-weekly and fortnightly assessments. Environmental conditions ranged from severe drought to average. Variation in the densities and distributions of the herbivore populations were assessed monthly in four large paddocks (total area 22 km2 ), two of which were unstocked. The paddocks incorporated footslope and flood plain habitat and comprised a mosaic of landclasses. Fifty-nine individual female kangaroos were radio-tracked in order to evaluate space and resource use at the individual level. The population of the most abundant native herbivore, the red kangaroo, was widely spread over the study site, with higher densities in the unstocked paddocks and flood plain habitat. The population was in decline and food-limited but showed no density dependence. The smaller western grey kangaroo population was more abundant in the stocked paddocks, favouring habitat with greater overhead cover and increased through the study. The euro population, comprised mostly large males on the foot slopes, and fluctuated in density and distribution according to environmental conditions. Eastern grey kangaroos and goats were rare and transient on the study site. Rabbits were limited in abundance due to low availability of suitable soils for warren building and subject to control by myxomatosis and the calici-virus. Stocking levels of sheep were set by management according to bloodlines and perceived quantity and quality of pasture. Sheep stocking increased significantly in one paddock over the study. Sheep activity centred on watering points and resting places, leading to uneven use of their available fenced habitat. The herbivores typically segregated except in time of food limitation. However, in the stocked paddocks pasture biomass was always above the threshold of exploitative competition between sheep and kangaroos estimated for arid chenopod shrublands. The grazing system revealed impacts by the herbivores on the pasture layer, but pasture biomass dynamics were not governed by current herbivore densities. No evidence was found for kangaroo damage on the pasture layer, but rather a facilitative effect on aboveground productivity. In contrast sheep produced some facilitative effects, but had more grazing impact. Sheep interfered with kangaroo activity and probably displaced them from some habitat. Most interactions between herbivores were neutral and differences in productivity of paddocks was likely based on past pastoral practices, i.e. grazing history, and its consequences to soils and vegetation composition, rather than current abundance of herbivores.

Mots clés : Mammals - Herbivores - Kangaroos - Sheep - Goats - Rabbits - New South Wales


Accès au document : Proquest Dissertations & Theses

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