Dingo (Canis dingo) extirpation and associated trophic restructuring as a mechanism influencing direct and indirect effects on mammal assemblages in Australia

Large mammalian carnivores can initiate trophic cascades that influence the abundance and behaviours of species occupying multiple trophic levels in ecosystems. Although these apex predators often play key roles in ecosystems, many have been extirpated from vast areas of the Earth due to conflict with local people. Extirpation of apex predators from areas where they were once prevalent has often resulted in ecosystem restructuring and loss of biodiversity.Apex predators impact other animals through killing, and through indirect effects such as precipitating fear induced behavioural and physiological changes, which reduce the fitness of smaller predators. These effects often result in subsequent changes to other trophic interactions. Large carnivores can limit populations of large herbivores through predation, and mesocarnivores through intra-guild competition, thus influencing the structure of ecosystems along multiple food-web pathways. In this thesis, I explore the hypothesis that the functional extinction of Australia’s largest terrestrial predator, the dingo (Canis dingo), drives shifts in ecosystem structure. Specifically, I test two hypotheses (i) that dingoes (12 – 22 kg) supress feral cat (Felis catus; 3 – 6 kg) mesopredators, thereby facilitating an increase in the abundance of a suit of small to medium sized animals and; (ii) dingoes direct predation on herbivorous macropods (17 -19 kg) reduces abundances, indirectly reducing grazing and increasing micohabitat availability. Although the effects of dingoes on other species has been well researched in desert and forest ecosystems, the dingoes’ ecological role in the tropics remains poorly understood. To address this gap in knowledge, I focused my research in the northern tropics of Australia. In Chapter 1, I overview the current status and knowledge of top predators as drivers of trophic restructuring and the different theories of how this occurs. In Chapter 2, I write a brief overview of the impact of dingo removal from tropical regions in Australia and compare to desert and forest ecosystems. My results suggest that dingoes’ suppressive effects on macropods and mesopredators occur simultaneously, indirectly benefiting small mammals and native rodents through a reduction in predation pressure and an increase in microhabitat availability. In chapter 3, I examine the impacts of dingo removal on rodent abundance in tropical northern Australia. Results from this chapter indicate that rodent decline is linked to two mechanisms; increased predation by irrupting populations of feral cats and a reduction in available habitat from overgrazing by larger number of herbivorous macropods, following elimination of predation pressure from dingoes. In the remaining chapters I examine the indirect effects of predation, such as fear induced behavioural changes. Specifically, I test the theory that in addition to the lethal effects of killing them, the presence of the larger bodied dingo may alter the behaviour of macropod prey and the smaller red fox. Results for these final chapters provide support for the idea that dingo odour exerts a strong interference effect on both red foxes and macropod prey, although the extent of the response varied