This article provides a context to, attempts an explanation for, and proposes a response to the recent demonstration of rapid and severe decline of the native mammal fauna of Kakadu National Park. This decline is consistent with, but might be more accentuated than, declines reported elsewhere in northern Australia; however, such a comparison is constrained by the sparse information base across this region. Disconcertingly, the decline has similarities with the earlier phase of mammal extinctions that occurred elsewhere in Australia. We considered four proximate factors (individually or interactively) that might be driving the observed decline: habitat change, predation (by feral cats), poisoning (by invading cane toads), and novel disease. No single factor readily explains the current decline. The current rapid decline of mammals in Kakadu National Park and northern Australia suggests that the fate of biodiversity globally might be even bleaker than evident in recent reviews, and that the establishment of conservation reserves alone is insufficient to maintain biodiversity. This latter conclusion is not new; but the results reported here further stress the need to manage reserves far more intensively, purposefully, and effectively, and to audit regularly their biodiversity conservation performance.

Aim  To assess whether eight factors thought to be involved in the extinction process can explain the pattern of recent decline in Australia's mammal fauna. Location  Australia. Methods  We compiled the first comprehensive lists of mammal species extant at the time of European settlement in each of Australia's 76 mainland regions, and assigned a current conservation status to each species in each region to derive an index of faunal attrition. We then sought to explain the observed region‐to‐region variation in attrition (the dependent variable) by building a series of models using variables representing the eight factors. Results  A strong geographically based pattern of attrition emerged, with faunal losses being greatest in arid regions and least in areas of high rainfall. The Akaike information criterion showed support for one model that explained 93% of the region‐to‐region variation in attrition. Its six variables all made independent contributions towards explaining the observed variation. Two were environmental variables, namely mean annual rainfall (a surrogate for regional productivity) and environmental change (a measure of post‐European disturbance). The other four were faunal variables, namely phylogenetic similarity, body‐weight distribution, area (as a surrogate for extent of occurrence), and proportion of species that usually shelter on the ground (rather than in rock piles, burrows or trees). Main conclusions  In combination with historical evidence, the analysis provides an explicit basis for setting priorities among regions and species. It also shows that the long‐term recovery of populations of many species of Australian mammals will require introduced predator suppression as well as extensive habitat management that includes controlling feral herbivores. Specifically, habitat management should restore aspects of productivity relevant to the types of species at risk and ensure the continual availability of suitable refuges from physiological stressors.

This paper attempts to identify and explain patterns in the biogeography of Australia’s indigenous terrestrial mammals at the time of European settlement (before modern extinctions), and also compares species’ pre-European and current status by region. From subfossil, historical and contemporary sources, we compiled data on the past geographic range and present status of mammals for Australia’s 85 biogeographic regions. Of the 305 indigenous species originally present, 91 have disappeared from at least half of the bioregions in which they occurred before European settlement. Thirty-nine extant species ‘persist’ in less than 25% of their original bioregions; 28 of these are marsupials and 11 are rodents. Twenty-two of the original 305 species are extinct, a further eight became restricted to continental islands, and 100 have become extinct in at least one bioregion. Over the same period, 26 species of exotic mammals established wild populations and now occupy from one to 85 bioregions. When we classified the bioregions in terms of their original species composition, the 3-group level in the dendrogram approximated the Torresian, Eyrean and Bassian subregions proposed by Spencer in 1898, while the 4-group level separated southern semiarid Eyrean bioregions, including those in south-west Australia, from the arid Eyrean bioregions. The classification dendrogram showed geographically (and statistically) discrete clustering down to the 19-group level, suggesting that all four subregions can be further divided on the basis of their mammal faunas. Variation partitioning showed 66% of the biogeographical pattern can be explained by environmental factors (related to temperature and precipitation), the spatial position of each bioregion (a third-order polynomial of latitude and longitude), the area of each bioregion, and the richness of species in each bioregion. In addition to the marked distributional changes that indigenous mammals have experienced over the last 200 years, the 49% of variation explainable by temperature and precipitation implies further shifts with global climate change.

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