Anthony D. Griffiths

Monitoring indicates rapid and severe decline of native small mammals in Kakadu National Park, northern Australia

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.

Cane toads reduce the abundance and site occupancy of Merten's water monitor (Varanus mertensi)

Introduced into Australia in 1935, the cane toad (Chaunus [Bufo] marinus) threatens native vertebrate predators. However, there have been few rigorous quantitative studies on species threatened by this toxic invasive species. This study examines the changes in abundance and proportion of sites occupied by Merten’s water monitor (Varanus mertensi) at a site in the Northern Territory following invasion by cane toads. The study was located at Manton Dam Recreation Area, 70 km south of Darwin, and ran for 18 months. Cane toads were first detected at the study site in February 2005, three months after the first survey, and their abundance remained low until February 2006, when an increase was observed. The abundance of V. mertensi declined substantially 8 months after the arrival of cane toads and remained low. The probability of detection of V. mertensi varied considerably within and among surveys, and was higher in the wet season surveys. The proportion of sites occupied by V. mertensi at the start of the study was 0.95 ± 0.03. Site occupancy remained high for 6 months after the arrival of cane toads, but declined gradually to a low of 0.15 ± 0.16 within 12 months. There has been demonstrable change in the abundance and proportion of sites occupied by V. mertensi following the colonisation of cane toads, but the population has been able to persist. Monitoring of populations impacted by cane toads may provide unique opportunities to understand processes underlying local extinction and colonisation of native predators following the impact of invasive species.

Diet and habitat use of frillneck lizards in a seasonal tropical environment

A population of frillneck lizards, Chlamydosaurus kingii, was monitored by mark-recapture and telemetry over a 2 year period in Kakadu National Park. The aims of the study were to document changes in diet, growth, condition and habitat use between the wet and dry seasons of northern Australia, in light of recent research examining seasonal variation in the physiology of this species. Frillneck lizards feed on a diverse range of invertebrates in both seasons, even though there is a substantial reduction in food avail-ability in the dry season. Harvester termites from the genus Drepanotermes constitute a major component of the diet, and the prevalence of termites in the diet of sedentary foragers in a tropical environment is unusual. Adult male body condition remained relatively stable throughout the year, but females experienced considerable variation. These differences are attributed to different reproductive roles of the sexes. Growth in C. kingii was restricted to the wet season, when food availability was high, and growth was minimal in the dry season when food availability was low. The method used in catching lizards was an important factor in determining seasonal habitat use. Telemetered lizards selected a significantly different distribution of tree species than was randomly available, and they selected significantly larger tree species during the dry season. Lizards spotted along roadsides showed little seasonal variation in the selection of tree species or tree sizes. The results suggest a comprehensive change in the ecology of this species, in response to an annual cycle of low food and moisture availability, followed by a period with few resource restrictions.

The terrestrial vertebrate fauna of Litchfield National Park, Northern Territory: monitoring over a 6-year period and response to fire history

Forty-seven 50 m × 50 m quadrats were sampled systematically for vertebrates at Litchfield National Park, northern Australia, in both 1995–96 and 2001–02. A total of 184 vertebrate species was recorded from this sampling, of which 92 species were recorded from five or more quadrats. There was substantial change in the reported species composition of these quadrats between these two periods: the mean Bray–Curtis index for similarity in species composition from the baseline to subsequent sampling of a quadrat was only 22.1 (for an index that varies from 0 for complete turnover in species to 100 for unchanged composition). For individual species, correlations across quadrats in the abundance scores from baseline to resampling varied from –0.12 to 0.85. Matched-pairs testing showed that there was significant change in abundance for 18 species from the baseline to repeat sampling, and significant increase in total bird species richness and total native mammal abundance, but significant decrease in reptile species richness. Fire history was recorded biannually for 40 of the 47 quadrats. Fire was very frequent, with quadrats being burnt in an average of 3.65 years of the six years between fauna samples. Three aspects of this fire history (total number of years of fires, number of fires in the late dry season, and interval from the last fire to the date of resampling) were related to change in the fauna composition of quadrats. Neither the similarity in species composition, nor change in richness or total abundance of all vertebrates or of the four taxonomic classes considered (frogs, reptiles, birds and mammals) were significantly correlated with these components of the fire history of sampled quadrats. This lack of association was possibly because the monitoring period was too short to show pronounced directional change, because the system was responding to many factors other than fire, because the variations in abundance were too large and the number of samples too small to detect true associations, or because fire histories preceding baseline sampling were not considered. The apparent instability of fauna species and communities in this system provides a considerable challenge for broad-brush (that is, vertebrate community–wide) monitoring. Power analysis demonstrated that, for most species, more than 1000 sample sites are needed to be 90% certain of detecting a 20% change in abundance, and with a 10% chance of accepting a Type I error. This level of sampling effort is commensurate with the current level of vertebrate sampling in this region. Broad-brush monitoring approaches such as described here are valuable, but need also to be complemented by more targetted monitoring for individual threatened species or species of particular management interest.

Physiological ecology of frillneck lizards in a seasonal tropical environment

The frillneck lizard, Chlamydosaurus kingii, is a conspicuous component of the fauna of the wetdry tropics of northern Australia during the wet season, but it is rarely seen in the dry season. Previous studies have demonstrated that during the dry season the field metabolic rate (FMR) is only about one-quarter of the wet-season rate, and one factor involved in this seasonal drop is a change in the behavioural thermoregulation of the species such that lower body temperatures (Tbs) are selected during dry-season days. Here we examine other factors that could be responsible for the seasonal change in FMR: standard metabolic rates (SMR) and activity. Samples from stomach flushing revealed that the lizards in the dry season continued to feed, but the volume of food was half as much as in the wet season. SMR in the laboratory was 30% less in the dry season. During the dry season, the energy expended by the lizards is 60.4 kJ kg-1 day-1 less than during the wet season. Combining laboratory and field data, we determined the relative contribution of the factors involved in this energy savings: 10% can be attributed to lower nighttime Tb, 12% is attributable to lower daytime Tb, 12% is attributable to decreased metabolism, and the remaining 66% is attributable to other activities (including e.g. locomotion, reproductive costs, digestion). Calculations indicate that if FMR did not drop in the dry season the lizards would not survive on the observed food intake during this season. Seasonal analysis of blood plasma and urine indicated an accumulation of some electrolytes during the dry season suggesting modest levels of water stress.

An analysis of the use of plant products for commerce in remote Aboriginal communities of northern Australia

The indigenous people of Australia have a long and well documented history of using native plants as an essential component of their customary economy. However, few have engaged successfully in commerce based on native plant use. Recently there has been an increasing interest in exploring options for use of native plants for food, food additives, botanical medicines, and related purposes. In this paper, we determine the issues important to Aboriginal people in enterprise development utilizing plant products, and we define some of the factors affecting progress in realizing opportunities. The Aboriginal people with whom we have worked appear to prefer small-scale enterprises where they have community ownership of ideas and control of the rate and direction of development. Government could play a larger and more active role through supporting additional research and marketing information, providing training, and better matching policy and legislation to support indigenous development and reduce dependence of welfare.

Harvest of Bombax ceiba for the Aboriginal arts industry, central Arnhem Land, Australia

Aboriginal people in remote Australian communities have limited opportunity to participate in the market economy. The Aboriginal arts and craft industry offers an important option to generate cash income and the sustained supply of native plants used in production is vital. We assessed the current harvest of a rainforest tree species commonly used for sculpture, Bombax ceiba. Information from field surveys, a regional rainforest inventory and sales figures from the Maningrida region were used to estimate the population size and structure of B. ceiba, the harvest intensity of. patches and the economic value of the harvest. We estimate the density of B. ceiba to be 105.10 +/- 12.32 stems ha(-1) and a regional population of 76615 +/- 14063 stems. A cumulative harvest over 20 years of 6% suggests approximately 4596 stems harvested, and the harvest was worth about

Large-scale dieback of mangroves in Australia’s Gulf of Carpentaria: a severe ecosystem response, coincidental with an unusually extreme weather event

200,000 over the last three years. The majority (80%) of harvested stems coppiced and were suitable for harvesting. Logistic regression suggests both distance to outstation and township influence harvesting intensity, with some localised over-harvest. Rainforests provide a valuable resource to Aboriginal artists in Maningrida and their maintenance provides important conservation benefits to the Australian community

Effect of fire on small mammals: a systematic review

This study records and documents the most severe and notable instance ever reported of sudden and widespread dieback of mangrove vegetation. Between late 2015 and early 2016, extensive areas of mangrove tidal wetland vegetation died back along 1000km of the shoreline of Australia’s remote Gulf of Carpentaria. The cause is not fully explained, but the timing was coincident with an extreme weather event; notably one of high temperatures and low precipitation lacking storm winds. The dieback was severe and widespread, affecting more than 7400ha or 6% of mangrove vegetation in the affected area from Roper River estuary in the Northern Territory, east to Karumba in Queensland. At the time, there was an unusually lengthy period of severe drought conditions, unprecedented high temperatures and a temporary drop in sea level. Although consequential moisture stress appears to have contributed to the cause, this occurrence was further coincidental with heat-stressed coral bleaching. This article describes the effect and diagnostic features of this severe dieback event in the Gulf, and considers potential causal factors.

Production from marginal lands: indigenous commercial use of wild animals in northern Australia

Fire is a natural disturbance that exerts an important influence on global ecosystems, affecting vegetation distribution and structure, the carbon cycle and climate. However, human-induced changes to fire regimes may affect at-risk species groups such as small mammals. We examine the effect of fire on small mammals and evaluate the relative sensitivity to fire among different groups using a systematic review methodology that included critiquing the literature with respect to survey design and statistical analysis. Overall, small mammal abundance is slightly higher, and demographic parameters more favourable, in unburnt sites compared to burnt sites. This was more pronounced in species with body size range of 101–1000g and with habitat requirements that are sensitive to fire (e.g. dense ground cover): in 66.6 and 69.7% of pairwise comparisons, abundance or a demographic parameter were higher in unburnt than burnt sites. This systematic review demonstrates that there remains a continued focus on simple shifts in abundance with regards to effect of fire and small mammals, which limits understanding of mechanisms responsible for change. Body size and habitat preference were most important in explaining variation in small mammal species’ responses to fire.