Chapter 1: Introduction 1 Chapter 1 Introduction 1.1 General introduction Forty-two species of mammals worldwide have suffered extinction since 1600 (IUCN 2003). Almost half of the world’s mammal extinctions in the last two hundred years have occurred in Australia, coinciding with European settlement of the continent (Short and Smith 1994). Seventeen species are extinct, 10 survive only as island populations, and a further 17 have been reduced to remnant populations of less than 10% of their range prior to European settlement. The decline and extinction of these species has been documented by a number of early authors (e.g. Finlayson 1935, 1961; Jones 1923-25; Krefft 1866; Shortridge 1909), and has typically been associated with the impact of European settlement of Australia. Soulé (1983, p. 112) noted: "As far as I know, no biologist has documented the extinction of a continental species of plant or animal caused solely by non- human agencies such as competition, disease or environmental perturbation in situations unaffected by man". Possible causes for the losses in our native mammal fauna have been widely debated over the last century, yet the causal factors for the decline and extinction of individual species are rarely known (Caughley and Gunn 1996). In many cases, the biology of a species has been so poorly known, that any threatening processes identified have been rarely more than a guess. Predation by introduced feral cats Felis catus and the European fox Vulpes vulpes, habitat modification and fragmentation (destruction by clearing for agriculture, the impacts of introduced livestock and European rabbits Oryctolagus cuniculus, changes in fire regimes), competition from introduced species, hunting pressure, pest control, pollution, and disease, or a combination of any of these factors, have commonly been implicated in the loss of mammal species in Australia (e.g. Burbidge and McKenzie 1989; Caughley and Gunn 1996; Ride and Wilson 1982; Short and Turner 1992). Chapter 1: Introduction 2 For some species the threatening process or processes have been quantified. This knowledge has usually been gained by the removal of the putative threat. For example, black-footed rock-wallabies Petrogale lateralis were present in low numbers on granite outcrops in the wheatbelt of Western Australia. After the Department of Conservation and Land Management instigated fox control on two outcrops in the 1980s, rock- wallaby numbers increased by over 400%, while two populations without fox control declined (one to extinction) and a third population without fox control increased slightly (Kinnear, Onus and Bromilow 1988; Kinnear, Onus and Sumner 1998). The Lord Howe Island woodhen Gallirallus sylvestris was rescued from near-extinction by the removal of feral pigs from the island. Less than 30 woodhens were thought to remain in 1979, but with the removal of pigs from the island, the population was more than 200 by 1984 (Fullagar 1985). However, among a handful of success stories where threatening processes have been correctly identified, there are probably many more in which threats have been diagnosed incorrectly. Few of these examples are reported in the scientific or popular literature, providing little opportunity for others to learn from misdiagnoses and mistakes. Caughley and Gunn (1996 p. 14) suggested that “Sharing knowledge of failures is as important as successes, given the urgency of problems facing species in trouble.” They listed examples where guesses at causal factors have been incorrect, and have resulted in the further decline or ultimate loss of a species. For example, Arctic foxes Alopex lagopus were thought to be responsible for the decline of the Aleutian Canada goose Branta canadensis. The foxes were eradicated from four islands, but the decline continued. Hunting pressure at other locations was then discovered to be the threatening process (Caughley and Gunn 1996). Failures can often provide some insight into the threatening process or processes depressing a species’ numbers. For example, a reintroduction of 40 golden bandicoots Isoodon auratus and 40 burrowing bettongs Bettongia lesueur to the Gibson Desert in September 1992 failed within three months of the translocation (Christensen and Burrows 1994). Predation by foxes and changed fire regimes were thought to be the primary threatening processes in the demise of these species from mainland Australia, and as a consequence, the area was heavily baited with 1080 to control fox populations. However, in the absence of foxes, the number of feral cats increased. Cat predation was thought to be the primary cause of death of the translocated animals. Unfortunately, for Chapter 1: Introduction 3 many other reintroductions, there has been a lack of experimental investigation into the causes of decline and reasons for failure, and animals are lost with little knowledge gained (Armstrong, Soderquist and Southgate 1994; Caughley 1994). The discipline of conservation biology was established to address the issues associated with the decline and extinction of species, the subsequent loss of biological diversity, and the consequences of these losses on ecosystem function throughout the world. Historically, mammal conservation was centred around the protection of species from hunting and trade, land acquisition for nature conservation, and fauna surveys to map distribution and abundance, however recent successes have been a result of the effective control of exotic predators (Short and Smith 1994). Dickman (1996) delineated two basic approaches to halting the loss of species: identifying and preserving areas of high conservation value (Humphries, Williams and Vane-Wright 1995), or listing species (or some form of biologically or genetically recognised group) that are threatened with extinction, and attempting their recovery. These approaches have advantages and failings, and have been the subject of ongoing discussion within the scientific, wildlife management, and political arenas. The sphere of conservation biology is influenced by economics and politics. The hope is that scientists become more able to influence where money is best spent. Whatever the outcome, basic research on the ecology of species and their ecosystems is required before conservation effort can truly be effective. 1.2 The small and declining population paradigms Caughley (1994) and Caughley and Gunn (1996 p. 3, 4) outlined two paradigms of conservation biology. “The declining-population paradigm deals with why the population is declining or has already declined to low numbers, what caused it, and what might be done to reverse the decline.” Its focus lies within the field of wildlife management: defining threatening processes and removing them or managing them in such a way as to reverse the decline. It has been regarded as a practical approach to species conservation, based on day-to-day management practices that directly assist with on-ground conservation of a species or community. By contrast, the small population paradigm encompasses “the ideas dealing with the effect of low numbers as such upon a population’s persistence.” Demographic and Chapter 1: Introduction 4 environmental stochasticity, inbreeding depression, and genetic drift are the primary factors that are regarded as influencing the size of the population. The reason why it is small in the first place is not the issue; managing the small population to maintain its viability is the main concern. The work outlined within this thesis falls predominantly into the declining population paradigm. The future of threatened mammals on mainland Australia lies in determining the factors that have limited or are limiting their survival. While small populations may need to be managed to avoid extinction, the very nature of declining populations means that their persistence may not be ensured unless the threats to their survival are removed. If factors causing the decline cannot be removed, the only option available may be to manage the population to prevent the problems commonly associated with small population size. The ultimate aim is to increase the size of small populations and avoid the inherent problems associated with being small. 1.3 Reintroduction as a tool in conservation biology Ride (1970) outlined three steps to address the conservation of threatened mammals in Australia: 1. Survey to acquire information on distribution, abundance and habitat; 2. Gather biological data for each species; and 3. Design management programmes for species and set aside reserves to provide for their permanent conservation. Caughley (1994) suggested a series of actions to both assist in the diagnosis of decline, and the recovery of threatened species: 1. Confirm the species is in decline, or has previously declined; 2. Study the natural history of the species to increase knowledge of its ecology, context, and status; 3. When adequate background knowledge is available, list all conceivable agents of decline; 4. For each agent, measure its level where the species persists and where the species used to be in time or space. Any contrast may indicate an agent of decline; and Chapter 1: Introduction 5 5. Test the hypothesis by experiment to confirm that the agent is causally linked to the decline, not simply associated with it. Once the threatening process or processes have been determined, the final step is to reverse the decline by removing or neutralising the agents of decline (Caughley and Gunn 1996). After background information for threatened species has been gathered,