Dingo (Canis dingo) extirpation and associated trophic restructuring as a mechanism influencing shrub encroachment in arid Australia

Abstract

Large mammalian carnivores can initiate trophic cascades which influence the abundance of species occupying multiple trophic levels in ecosystems. Although these 'top predators' often play keystone roles within ecosystems, they have been extirpated from vast areas of the Earth due to conflict with pastoralists and habitat modification. The extirpation of top predators from areas where they were once common has often resulted in ecosystem restructuring and loss of biodiversity. Shrub encroachment is a global phenomenon characterised by increases in the density of woody plants at the expense of grasses. Although top predator extirpation and shrub encroachment co-occur in many areas of the Earth, top predator extirpation has yet to be tested as a mechanism influencing shrub encroachment. In this thesis I explore the hypothesis that the functional extinction of Australia's largest terrestrial predator, the dingo (Canis dingo), has indirectly benefited the recruitment and ultimately the abundance of encroaching shrub species in areas of the Strzelecki Desert. Specifically, I test the hypothesis that dingoes (12 - 22 kg), by suppressing the abundance of red fox (Vulpes vulpes; 5 - 7 kg) and feral cat (Felis catus; 3-6 kg) mesopredators, facilitate an increase in the abundance and consumptive impact of browsing rabbits and granivorous rodents on shrub seedlings and seeds. Much of my research uses Australia's dingo-proof fence as a pre-established experimental treatment. The dingo-proof fence is over 5000 km long and was constructed in the early 1900s to exclude dingoes from sheep grazing areas of New South Wales, South Australia and Queensland. The dingo-proof fence provides an ideal setting to test hypotheses regarding dingo effects in arid Australian ecosystems because dingoes have been and remain historically rare to the south and east of the fence ('inside' the dingo-proof fence), but have remained common in adjoining areas to the north and west of the fence ('outside' the dingo-proof fence).

Date of Award	2015
Original language	English