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.

This paper provides an introduction to the ecological fabric of northern Australia, described here as being a land characterised by extreme climatic seasonality and largely devoid of marked topographic features. Largely as a result of the latter trait, many species have extensive geographic ranges, and the spatial turnover in species composition is extremely limited. Somewhat counter-intuitively, these two traits can be accommodated by organisms only through reliance on critical, but often subtle, landscape variation. We present some preliminary models for Gouldian finch (Erythrura gouldiae) and black-footed tree-rat (Mesembriomys gouldii) to illustrate patterns of variation in their resource availability, and the consequences of such variation. We discuss briefly some studies that have attempted to integrate, or at least consider, these elements.

Translocation is a strategy commonly used to maximize the persistence of threatened species, but it may sometimes lead to undesirable genetic consequences. The northern quoll (Dasyurus hallucatus) is a carnivorous marsupial that is critically endangered in Australia's Northern Territory due to rapid population declines in areas recently colonized by the exotic cane toad Chaunus [Bufo] marinus. In 2003, 64 quolls were translocated to two offshore islands to establish insurance populations and reduce the species' risk of extinction. In this study, we assessed genetic diversity at five microsatellite loci in the translocated populations, two endemic islands and three mainland populations. In the short-term (three generations), the translocated populations showed a slight but non-significant reduction in genetic diversity (A = 4.1-4.2; H e = 0.56-0.59) compared to the mainland source populations (A = 5.0-8.4; H e = 0.56-0.71). In comparison, high genetic erosion was observed in the endemic island populations (A = 1.5-2.9; H e = 0.11-0.34). Genetic bottlenecks were detected on both endemic islands and in one mainland population, indicating recent reductions in population size. Our results are consistent with previous studies describing greater losses of genetic diversity on islands compared to mainland populations. Divergence from ancestral allele frequencies in the translocated populations also suggests effects due to founder events. This study, although short-term, highlights the importance of continued monitoring for detecting changes in genetic diversity over time and makes a significant contribution to our understanding of the effects of founder events on island populations.

Context Translocation is widely used to help avoid extinction of species from threatening processes. A fundamental objective of translocation is to establish self-sustaining populations; estimating demographic parameters is critical to assessing success of these programs and can also be used to support future management actions. Aims We estimated demographic parameters to evaluate the success of translocating the northern quoll Dasyurus hallucatus to two islands (Astell and Pobassoo), in response to the threat posed by the introduced cane toad Rhinella marina on the Australian mainland. Methods We used capture–mark–recapture methods to monitor both populations at regular intervals from initial release in 2003 until 2009 and a one-off survey in 2014. Key results Relative abundance (trap success) increased exponentially in the first 4 years, declined, and then stabilised in subsequent years. The population of female northern quolls on Astell Island peaked in 2006 with an estimate of 3640 (95% CI 3022–4257), and on Pobassoo Island the peak was 2007 with 617 (95% CI 531–703) females. In 2014 the population had decreased to 2193 (95% CI 1920–2467) on Astell and 451 (95% CI 359–543) on Pobassoo. Apparent survival and body condition decreased significantly following the population peak, possibly related to density dependence. Conclusion Both populations of northern quolls reached their regulation phase after going through establishment and growth phases, which included exceeding carrying capacity. The pattern was similar between the populations. Implications Increased survival and recruitment at threat-free translocation sites contributes to successful establishment of self-sustaining populations.