Antechinus

Abstract: A previous study (Braithwaite & Muller 1997) reported substantial declines in mammal abundance over the period 1986-1993 for a large study area (300 km 2 ) within Kakadu National Park in the tropical savannas of northern Australia. This decline was reported as being a 'natural' response to fluctuating groundwater levels, driven by runs of poor wet seasons. We resampled mammals in this area in 1999, following a series of unusually good wet seasons, and examined the prediction that mammal numbers should have recovered. Increases in abundance were evident for four species: the smallest dasyurid (red-cheeked dunnart Sminthopsis virginiae) and the three smallest rodents (delicate mouse Pseudomys delicatulus, western chestnut mouse Pseudomys nanus and grassland melomys Melomys burtoni). In contrast, the abundance of all mammals combined and that for seven individual mammal species (northern quoll Dasyurus hallucatus, fawn antechinus Antechinus bellus, common brushtail possum Trichosurus vulpecula, northern brown bandicoot Isoodon macrourus, dusky rat Rattus colletti, black-footed tree-rat Mesembriomys gouldii and pale field rat Rattus tunneyi) continued to decline. The decline in abundance of these mammal species is consistent with limited observations elsewhere in northern Australia. Although far from conclusive, these observations suggest that the biota of the vast relatively undisturbed tropical savannas can no longer be assumed to be intact nor safe. Further research is needed to test this possible pattern of decline and, if confirmed, to identify and ameliorate the processes contributing to it.

Abstract: Context. Australia has a lamentable history of mammal extinctions. Until recently, the mammal fauna of northern Australia was presumed to have been spared such loss, and to be relatively intact and stable. However, several recent studies have suggested that this mammal fauna may be undergoing some decline, so a targeted monitoring program was established in northern Australia’s largest and best-resourced conservation reserve. Aims. The present study aims to detect change in the native small-mammal fauna of Kakadu National Park, in the monsoonal tropics of northern Australia, over the period of 1996–2009, through an extensive monitoring program, and to consider factors that may have contributed to any observed change. Methods. The small-mammal fauna was sampled in a consistent manner across a set of plots established to represent the environmental variation and fire regimes of Kakadu. Fifteen plots were sampled three times, 121 plots sampled twice and39plotsonce.Resamplingwastypicallyat5-yearlyintervals.Analysisusedregression(ofabundanceagainstdate),and Wilcoxon matched-pairs tests to assess change. For resampled plots, change in abundance of mammals was related to fire frequency in the between-sampling period. Key results. A total of 25 small mammal species was recorded. Plot-level species richness and total abundance decreased significantly, by 54% and 71%, respectively, over the course of the study. The abundance of 10 species declined significantly, whereas no species increased in abundance significantly. The number of ‘empty’ plots increased from 13% in 1996 to 55% in 2009. For 136 plots sampled in 2001–04 and again in 2007–09, species richness declined by 65% and the total number of individuals declined by 75%. Across plots, the extent of decline increased with increasing frequency of fire. The most marked declines were for northern quoll, Dasyurus hallucatus, fawn antechinus, Antechinus bellus, northern brown bandicoot, Isoodon macrourus, common brushtail possum, Trichosurus vulpecula, and pale fieldrat, Rattus tunneyi. Conclusions. The native mammal fauna of Kakadu National Park is in rapid and severe decline. The cause(s) of this declinearenotentirelyclear,andmayvaryamongspecies.Themostplausiblecausesaretoofrequent fire,predationbyferal cats and invasion by cane toads (affecting particularly one native mammal species). Implications. The present study has demonstrated a major decline in a key conservation reserve, suggesting that the mammal fauna of northern Australia may now be undergoing a decline comparable to the losses previously occurring elsewhere in Australia. These results suggest that there is a major and urgent conservation imperative to more precisely identify, and more effectively manage, the threats to this mammal fauna.

Abstract: Wildfire is a major driver of spatio-temporal variation in terrestrial ecosystems. Large wildfires are predicted to occur more frequently due to climate change. The mechanisms by which post-fire recovery proceeds are influenced by the abundance of survivors, and their distribution in relation to habitat variability and refugia. Thus, characterising early post-fire demographic processes is critical to understanding the demographic and community-level responses of ecosystems to fire. The Black Saturday fires of February 2009 burnt an area of approximately 3500 km2 in Victoria, Australia. We quantified the effects of this high severity forest fire on the habitat, abundance, sex ratio and body mass of two small mammal species, the agile antechinus Antechinus agilis and bush rat Rattus fuscipes. We developed a hypothetical framework to distinguish in situ survival and rapid recolonisation as the processes underlying short-term post-fire distributions. These hypotheses were based on expected patterns of abundance over increasing distances from unburnt sources, and the estimated recolonisation capabilities of each species and sex. The agile antechinus and bush rat were present in burnt sites at 30% and 12% of the density observed in unburnt sites. In situ survival, and not recolonisation, was the most plausible explanation for our findings. Abundance and body mass data indicated a greater effect of fire on the bush rat than the agile antechinus. The bush rat showed a shift in topographic association, whereby drainage lines acted as post-fire refugia. Our findings suggest these species do not depend on recolonisation for recovery, and that the bush rat will follow a nucleated recovery, expanding from topographic refugia. Thus, connectivity-reducing management activities, such as salvage logging and firebreak and road construction, may not affect the early stages of population recovery in remaining stands of burnt forest. Rather, ongoing recovery is likely to be limited by demographic rates and resource availability.