Morphological variation and ecological interactions of Australia's apex predator - the dingo (Canis dingo)

Abstract

Apex predators are frequently keystone species that can have both direct and indirect impacts on other species within ecosystems. The disruption to species-interaction networks caused by irruptions of herbivores and mesopredators following the extirpation of apex predators is a global driver of ecosystem reorganisation and biodiversity loss. Australia's apex predator, the dingo (Canis dingo) influences the abundance and behaviour of herbivorous prey and mesopredators in arid ecosystems. The dingoes' ecological role is uncertain in more productive forested environments of eastern Australia. Here dingoes have undergone extensive hybridisation with domestic dogs and it is unclear to what extent hybridisation may have changed the morphology, behaviour and ecological effects of dingoes. This thesis aims to examine morphological variation in dingoes across Australia and the direct and indirect effects that dingoes have on the forested ecosystems of south-eastern Australia. Chapter 1 provides an overview of morphological variation in the size and shape of dingo skulls, in regards to hybridisation, environmental factors and land-use activities. Trophic cascade theory and the current management strategies for dingoes under NSW legislation are also addressed here. Chapter 2 investigates how spatial and environmental factors influence dingo skull morphology across Australia, and demonstrates that productivity is the overwhelming driver influencing skull size. In regards to hybridisation, forested regions of south-east Australia displayed a high incidence of skull characters indicative of hybridisation, whereas dingoes from other regions of Australia were largely similar in shape. Chapter 3 investigates the temporal variation in in the size of dingoes in arid Australia, using skull length as a proxy measurement of body size. Specifically, I investigated the temporal variation in dingo size, principally as a consequence of the use of poison fluoroacetate -1080. Smaller dingoes are more susceptible to lower doses of 1080 than larger dingoes. Thus, I hypothesised that the broad scale baiting of 1080 would select against smaller dingoes. Consistent with this hypothesis, I found that in baited areas dingoes were significantly larger over time, while no change in size was evident for non-baited areas. Chapters 4 and 5 examined the ecological role of the dingo in forested regions of south east Australia. Chapter 4 contrasted areas with long-term dingo control, against areas with no consistent control, while chapter 5 tested predictions generated from trophic cascade theory and the mesopredator release hypothesis using data extracted from published ecological datasets. The results of these chapters show that the effect of dingoes on the abundances of forest mammals scaled with body size. Where dingoes were abundant or in areas of no dingo control large herbivores, such as large macropods, and an introduced mesopredator, red fox (Vulpes vulpes), were less active/abundant. Conversely small and medium size ground dwelling mammals were more abundant where dingoes were common. In accord with trophic cascade theory, the complexity of understorey vegetation also tended to be greater where dingoes were abundant and or not controlled. Thus I concluded that the dingoes' suppressive effects on large herbivores and mesopredators occur simultaneously and hence have indirect effects on vegetation structure and ground-dwelling small and medium sized mammals. This study has implications for the management of dingoes within forest ecosystems as it provides evidence that ecological cascades, induced by the lethal control of an apex predator, can produce unintended shifts in the composition of species assemblages and vegetation structure. Chapter 6 provides a summation of these previous chapters, highlighting the implications and limitations of these studies, and provides direction for future work in this field.

Date of Award	2015
Original language	English