Semi-arid South Australia Research Articles

Sex-linked reproductive allocation in the dioecious shrub Pimelea microcephala subsp. microcephala (Thymelaeaceae) from four populations across a rainfall gradient

ABSTRACT Dioecy, the separation of sexes into different male and female plants, can enable sexes to independently develop optimal strategies for the sex-linked allocation of reproductive resources. Understanding how dioecious species vary as conditions become more or less favourable may affect conservation and revegetation efforts in arid environments. Our study investigated sex-related resource allocation in the Australian native shrub, Pimelea microcephala subsp. microcephala (Thymelaeaceae) at four sites across an annual rainfall gradient of 250–390 mm in semi-arid South Australia. The study measured 25 male and 25 female individuals for plant height, plant diameter, the number of inflorescences per plant, number of flowers per inflorescence and the ratio of reproductive to vegetative biomass. Significant differences in the ratio of biomass allocated to reproduction between sexes (p < 0.05) were detected at three of the four sites, with sex-related differences increasing with decreased annual rainfall. Female reproductive allocation was two to five times greater, and was less variable than males at all sites except the highest rainfall site (p < 0.05), while male reproductive allocation decreased with average annual rainfall (p < 0.05). Growth outcomes of males and females were equal and female reproductive traits were mostly consistent between sites and were not associated with rainfall, therefore population structure may remain stable for P. microcephala subsp. microcephala as habitats become drier, so long as pollen limitation does not occur.

Long-Distance Movements of Feral Cats in Semi-Arid South Australia and Implications for Conservation Management.

Simple SummaryTo efficiently control invasive animals, it is vital to have knowledge about their behaviour, their movements and how they use the landscape. Unusual behaviour is normally excluded from datasets, as it is considered to be an outlier that may distort analyses. In our study, we present movement data from feral cats in the arid and semi-arid zones of Australia. Feral cats are a serious problem to the native wildlife of Australia and in many parts of the world. Cats are known to show fidelity to geographic areas and may defend them against other cats. Until now, research has focused on these areas, home ranges or territories, that feral cats need to survive and reproduce. We argue that a part of their movement behaviour, large journeys away from the area they normally use, has been overlooked and has been considered to be unusual behaviour. We explain why we think that this is the case and present examples from other studies additional to our data set to show that these long-distance movements are a regular occurrence. To achieve a better protection of native wildlife from predation by feral cats, we believe that these long-distance movements should be considered as part of the normal behaviour of feral cats when planning cat control operations.Movements that extend beyond the usual space use of an animal have been documented in a range of species and are particularly prevalent in arid areas. We present long-distance movement data on five feral cats (Felis catus) GPS/VHF-collared during two different research projects in arid and semi-arid Australia. We compare these movements with data from other feral cat studies. Over a study period of three months in the Ikara-Flinders Ranges National Park, 4 out of 19 collared cats moved to sites that were 31, 41, 53 and 86 km away. Three of the cats were males, one female; their weight was between 2.1 and 4.1 kg. Two of the cats returned to the area of capture after three and six weeks. During the other study at Arid Recovery, one collared male cat (2.5 kg) was relocated after two years at a distance of 369 km from the area of collar deployment to the relocation area. The movements occurred following three years of record low rainfall. Our results build on the knowledge base of long-distance movements of feral cats reported at arid study sites and support the assertion that landscape-scale cat control programs in arid and semi-arid areas need to be of a sufficiently large scale to avoid rapid reinvasion and to effectively reduce cat density. Locally, cat control strategies need to be adjusted to improve coverage of areas highly used by cats to increase the efficiency of control operations.

Pasture plant biomass increase following introduction of European rabbit fleas, Spilopsyllus cuniculi, into Australia to facilitate myxomatosis transmission

Long-term benefits of introducing European rabbit fleas to Australia as vectors of myxomatosis have not been evaluated. To address this deficit, data on pasture plant biomass from a 21-year study in semi-arid South Australia was reviewed. A plant biomass index was derived from photographed quadrats on the site. Spring pasture biomass over a seven-year period before fleas were introduced was compared with pasture production over 14 years following their introduction after correcting for differences in rainfall. Plant biomass on the quadrats in spring (October) doubled after arrival of fleas presumably because high mortality of young rabbits reduced grazing pressure during the plant growing season; little dry plant material was carried over from previous years contrary to model outputs using the ‘Aussie GRASS’ program. Substantial benefits accrued from releasing rabbit fleas, especially in areas of Mediterranean-like climate in Western Australia, south-eastern South Australia and western Victoria where rabbit fleas changed the timing of myxomatosis outbreaks. Plant biomass saved from rabbits helped to maintain sheep production which was at an all-time high when fleas were released. Extra food may also have enabled native mammals such as swamp wallabies to expand their distribution soon after fleas became established.

Goat movement patterns inform management of feral goat populations in semiarid rangelands

Abstract ContextFeral goats (Capra hircus) are a significant pest species throughout southern Australia. They threaten rare plants, contribute to soil erosion, compete with domestic stock, and are implicated in the decline of several native herbivores. Feral goats are a declared pest and control is often implemented. AimsWe fitted feral goats with GPS collars in semiarid South Australia to determine whether they could provide valuable information for regional management. MethodsNineteen feral goats (6 males and 13 females) were fitted with GPS collars between 2009 and 2018. Kernel-density estimates (KDE) were used to estimate annual and seasonal home range and core areas and habitat selection. The effect of monthly rainfall, daily maximum temperatures, and watering points on movement patterns was investigated. Key resultsStock watering points and rock holes were used by some radio-tracked goats intermittently when available; however, goats survived and reproduced without the use of these water sources. The use of the radio-collared goats as Judas goats helped facilitate the removal of 9725 goats from a 50000-ha area over 8 years. There was no significant difference between male and female annual or seasonal home ranges, with 95% MCP annual ranges of 11533ha and 15996ha for males and females respectively. Summer ranges were smaller than winter ranges. There was no difference in daily distance moved between sexes (average 3.4km), but goats moved further in low-rainfall periods. Goats spent most of their time in mallee woodlands, the dominant habitat type available, but preferred shrubland of &amp;gt;1-m height and used less mallee woodland and shrubland of &amp;lt;1-m height than was expected from availability. During hotter periods, these habitat preferences became more distinct. ConclusionsTo reduce goat abundance on a property, active control and waterpoint closure need to extend more than 15km from property boundaries, and shrubland habitat of &amp;gt;1-m height should be targeted for control after rainfall events when goats move less. Radio-collared goats provided important habitat-preference information to inform priority areas for goat control remote from water sources. ImplicationsClosing artificial watering point and regular trapping and mustering at remaining waters is insufficient to remove residual goat herds without additional targeted control in preferred habitat.

Time to adjust: changes in the diet of a reintroduced marsupial after release

AbstractAn important component of reintroduction is acclimatization to the release site. Movement parameters and breeding are common metrics used to infer the end of the acclimatization period, but the time taken to locate preferred food items is another important measure. We studied the diet of a reintroduced population of brushtail possumsTrichosurus vulpeculain semi-arid South Australia over a 12 month period, investigating changes over time as well as the general diet. We used next-generation DNA sequencing to determine the contents of 253 scat samples, after creating a local plant reference library. Vegetation surveys were conducted monthly to account for availability. Dietary diversity and richness decreased significantly with time since release after availability was accounted for. We used Jacob's Index to assess selectivity; just 13.4% of available plant genera were significantly preferred overall, relative to availability. The mean proportion of preferred plant genera contained within individual samples increased significantly with time since release, but the frequency of occurrence of preferred plants did not. Five genera (Eucalyptus,Petalostylis,Maireana,ZygophyllumandCallitris) were present in more than half of samples. There was no difference in dietary preferences between sexes (Pianka overlap = 0.73). Our results suggest that acclimatization periods may be longer than those estimated via reproduction, changes in mass and movement parameters, but that under suitable conditions a changeable diet should not negatively affect reintroduction outcomes. Reintroduction projects should aim to extend post-release monitoring beyond the dietary acclimatization period and, for dry climates, diet should be monitored through a drought period.

How to snap your cat: optimum lures and their placement for attracting mammalian predators in arid Australia

Context Automatically activated cameras (camera traps) and automated poison-delivery devices are increasingly being used to monitor and manage predators such as felids and canids. Maximising visitation rates to sentry positions enhances the efficacy of feral-predator management, especially for feral cats, which are typically less attracted to food-based lures than canids. Aims The influence of camera-trap placement and lures were investigated to determine optimal monitoring and control strategies for feral cats and other predators in two regions of semi-arid South Australia. Methods We compared autumn and winter capture rates, activity patterns and behaviours of cats, foxes and dingoes at different landscape elements and with different lures in three independent 6 km × 3 km grids of 18 camera-trap sites. Key results Neither visual, olfactory or audio lures increased recorded visitation rates by any predators, although an audio and a scent-based lure both elicited behavioural responses in predators. Cameras set on roads yielded an eight times greater capture rate for dingoes than did off-road cameras. Roads and resource points also yielded highest captures of cats and foxes. All predators were less nocturnal in winter than in autumn and fox detections at the Immarna site peaked in months when dingo and cat activity were lowest. Conclusions Monitoring and management programs for cats and other predators in arid Australia should focus on roads and resource points where predator activity is highest. Olfactory and auditory lures can elicit behavioural responses that render cats more susceptible to passive monitoring and control techniques. Dingo activity appeared to be inversely related to fox but not cat activity during our monitoring period. Implications Optimised management of feral cats in the Australian arid zone would benefit from site- and season-specific lure trials.

DEVELOPING AGE-SIZE RELATIONSHIPS FOR LONG LIVED TREE SPECIES

Calculating the age of trees is often desirable in vegetation studies, but is sometimes difficult. In arid areas in particular, tree rings may not be annual, and growth may be related more to rainfall than annual cycles. A relationship between age and trunk circumference was developed for two species, Acacia aneura and Myoporum platycarpum, based on measurements of trees of known age (&lt;80 years) growing on permanent quadrats on the Koonamore Reserve, in semi-arid South Australia. Extrapolation beyond the known ages was made by finding the maximum girth of mature trees in a larger population and using this to estimate an asymptote to which the curve is constrained to approach. We envisage that the techniques developed here could be applied to other species of a similar nature, those for which there is no relationship between number of tree rings and age.

Daily food intake of free-ranging wild rabbits in semiarid South Australia

Context Although the daily food intake of wild rabbits is broadly known, precise field estimates have not been made. Moreover, regressions based on metabolic body size and food intake of grazing herbivores in general are too imprecise to provide close predictions. Using such values could result in substantial errors when estimating grazing equivalents to sheep or cattle and resultant economic losses, or estimating the numbers of rabbits per hectare based on rates of deposition of faeces. Aim To re-analyse previously collected data on estimated food digestibility and food intake of rabbits, and provide a framework for better estimating economic and conservation losses attributable to wild rabbits. Methods Food intake of wild free-ranging rabbits was calculated from past measurements of water turnover obtained from dilution of injected tritiated water and estimates of the water content and digestibility of the food eaten. Key results During spring, male rabbits were estimated to eat 65.7 ± 12.5 g dry matter per corrected bodyweight (W–0.75) per day and lactating females ate 97.0 ± 19.4 g dry matter W–0.75 day–1. Similar results were obtained on repetition of trials at a second field site and from wild rabbits held in captivity. Conclusions The estimates of food digestibility and intake obtained, although not precise, are an improvement on theoretical expectations alone and help put previously published data in better perspective. Implications Improved estimates of food consumption provide more confidence in estimates of rabbit grazing pressure. Even moderate densities of rabbits (5 rabbits per ha) could remove about half the pasture produced in an average year in Australia’s arid-zone.

Sediment residence times constrained by uranium-series isotopes: A critical appraisal of the comminution approach

Quantifying the rates of landscape evolution in response to climate change is inhibited by the difficulty of dating the formation of continental detrital sediments. We present uranium isotope data for Cooper Creek palaeochannel sediments from the Lake Eyre Basin in semi-arid South Australia in order to attempt to determine the formation ages and hence residence times of the sediments. To calculate the amount of recoil loss of 234U, a key input parameter used in the comminution approach, we use two suggested methods (weighted geometric and surface area measurement with an incorporated fractal correction) and typical assumed input parameter values found in the literature. The calculated recoil loss factors and comminution ages are highly dependent on the method of recoil loss factor determination used and the chosen assumptions. To appraise the ramifications of the assumptions inherent in the comminution age approach and determine individual and combined comminution age uncertainties associated to each variable, Monte Carlo simulations were conducted for a synthetic sediment sample. Using a reasonable associated uncertainty for each input factor and including variations in the source rock and measured (234U/238U) ratios, the total combined uncertainty on comminution age in our simulation (for both methods of recoil loss factor estimation) can amount to ±220–280ka. The modelling shows that small changes in assumed input values translate into large effects on absolute comminution age. To improve the accuracy of the technique and provide meaningful absolute comminution ages, much tighter constraints are required on the assumptions for input factors such as the fraction of α-recoil lost 234Th and the initial (234U/238U) ratio of the source material. In order to be able to directly compare calculated comminution ages produced by different research groups, the standardisation of pre-treatment procedures, recoil loss factor estimation and assumed input parameter values is required. We suggest a set of input parameter values for such a purpose. Additional considerations for calculating comminution ages of sediments deposited within large, semi-arid drainage basins are discussed.

Bringing Scholarship and Judgement into the Australian Population Debate

Video Abstract: http://bit.ly/ocGEkd

Loess and floods: High-resolution multi-proxy data of Last Glacial Maximum (LGM) slackwater deposition in the Flinders Ranges, semi-arid South Australia

Terrace remnants of late Pleistocene fine-grained valley-fill deposits (Silts) deeply entrenched by ephemeral traction load streams in arid areas remain a puzzle. They have been attributed to a variety of origins ranging from lacustrine to alluvial floodplains. We here report a centimetre-scale multi-proxy study of a 7 m section of Silts in the semi-arid Flinders Ranges of South Australia, which span the lead-up to and peak of the Last Glacial Maximum (LGM). The results of detailed lithostratigraphic mapping, high-resolution parametric particle-size analysis, Automated Mineralogy, induced magnetic susceptibility, carbon stable isotope geochemistry, and a chronostratigraphy based on 27 AMS radiocarbon and 6 luminescence ages are discussed in terms of sediment provenance, depositional environment and weathering history with the aim of reconstructing the regional palaeo-environment. The data are consistent with a fluctuating aeolian-fluvial interplay dominating the extended LGM environment with a greater impact on the landscape than all combined geomorphic processes since then. Accordingly, weathered slope mantles and loess accessions were eroded and entrained by numerous small and at least a dozen large-scale flood events, and trapped in an intra-montane floodplain extending into Brachina Gorge. Upstream of this narrow constriction, recurrent backflooding is discussed resulting in a thick sequence of layered to laminated slackwater couplets. Aggradation and degradation of valley-fills appear to be largely controlled by fine-sediment supply from the valley slopes, replenished by wind-blown dust from upwind playa lakes and source-bordering dunefields. In conclusion, this study demonstrates how dust storms and flooding rains can account for ‘pluvial’ features previously explained by the opposing effects of reduced precipitation and evaporation in the colder more arid glacial landscape of southern Australia.

A microbial pathway for the formation of gold-anomalous calcrete

The formation of pedogenic carbonate (calcrete) in terrestrial environments is commonly mediated by microorganisms. In Australia, Au-anomalous calcrete is an important sampling medium for geochemical exploration, but current models describing its formation do not include a confirmed microbial component. This study demonstrates that bacterial communities in calcareous sands from dunes overlying the Barns Gold Deposit in semi-arid South Australia, are capable of mediating the biomineralisation of Au-anomalous carbonates. Bacterial enrichment cultures obtained from calcareous sands at three depths (0.1, 0.64 and 2.1 m, plus abiotic control) were incubated in urea and Ca 2+-containing growth media (pH 8), unamended and amended with Au (100 parts-per-billion, ppb) as Au–aspartic-acid complex. During the incubation of the enrichment cultures urea was turned over to NH 4 + within 96 h to 220 h. The solution pH increased concurrently by approximately 1.2 units, and Au-anomalous Ca-carbonate crystallites were precipitated on cells, which functioned as nucleation sites; no carbonate precipitation was observed in abiotic controls. Compared to the medium, Au was strongly enriched in these carbonates and appeared to be uniformly dispersed in the individual crystallites, as shown using LA-ICP-MS; a similar distribution is present in naturally occurring Au-anomalous calcrete. Phylogenetic 16S rRNA PCR DGGE analyses, shotgun cloning and functional microbial analyses (BioLog, ureC quantitative PCR) demonstrated that naturally occurring and culture-enriched bacterial communities were dominated by alkaliphylic, halotolerant Bacillus spp. The indigenous bacterial communities were capable of utilising amino acids (including l-aspartic acid) and urea, which appears to lead to the destabilisation of the Au–amino acid complexes and concomitant co-precipitation of Au in the Ca-carbonates. In conclusion, a model combining geomicrobial– with evapotranspiration– and plant-based components is likely to best describe the formation of (Au-anomalous) calcrete in semi-arid and arid zones.

REPRODUCTION BY A SMALL AGAMID LIZARD, CTENOPHORUS PICTUS, DURING CONTRASTING SEASONS

Reproduction in a population of painted dragons, Ctenophorus pictus (Agamidae), in semi-arid South Australia was studied over two years with distinctly contrasting climatic conditions. Data were collected from wild lizards to assess the influence of inter- and intra-seasonal conditions on reproductive characters of the small, short-lived lizard during a very wet year and a season with average rainfall. Females began to develop ova at the end of winter (August) and laid eggs during the spring and early summer, coinciding with the period of testicular enlargement in males. Potentially four, or possibly more, clutches of 2 to 4 eggs (mean 2.6) were produced by females each year. Egg moisture content varied considerably and ranged between 45 and 79% (mean 66%) of total egg mass. Eggs contained less moisture in the wet year (1992–93). Females containing oviducal eggs were marginally larger in the wet year of 1992–93 than in 1991–92. Eggs collected late in the reproductive season were significantly larger than those collected earlier. A ‘parental investment’ model can be used to explain this intra-seasonal shift in egg size. When adjustments for female size were made, reproductive investment was consistent between the two years of the study, with no difference in egg mass, clutch mass or clutch size detected. The reproductive strategy of C. pictus remained remarkably invariant considering the dramatic difference in climatic conditions between the two years of the study.

Burrow use and ranging behaviour of the southern hairy‐nosed wombat ( Lasiorhinus latifrons ) in the Murraylands, South Australia

This study investigated burrow use and ranging behaviour in the southern hairy-nosed wombat Lasiorhinus latifrons in semi-arid South Australia. Sixteen adult wombats were fitted with radio transmitters and monitored monthly from July 2001 to February 2002. Wombats generally used between one and five warrens, preferred large warrens with a greater number of entrances and showed a preference for one or two warrens. Across the study period there was no apparent change in burrows used within warrens. Radio-tracking indicated that animals spent very little time above ground (26% of 1115 night-time fixes), centred their activity around their preferred warrens, and moved, on average, 99 m/h and 221 m/night. Mean home-range size, estimated using minimum convex polygons and the harmonic mean method from location data, obtained through triangulation, and daytime warren fixes, ranged from 1.3 to 4.8 ha. Home-range size was similar between males and females and home ranges overlapped substantially. The data highlight the importance of burrows to southern hairy-nosed wombats in shaping their home ranges. It seems likely that the use of burrows and a specialized diet are important energy saving strategies for this species in such unpredictable regions of South Australia.

Disarticulation of kangaroo skeletons in semi-arid Australia

This study presents a natural disarticulation sequence for the western grey kangaroo, Macropus fuliginosus, from surface bone assemblages in semi-arid South Australia. Comparison with published disarticulation sequences for African ungulates reveals significant differences in the kangaroo sequence, including earlier disarticulation of the forelimb long bones, carpus and cervical elements, and later disarticulation of the caudal vertebrae, and hindlimb long bones. These differences closely correspond to anatomical and morphological features of the kangaroo skeleton. The results of this study suggest that anatomy plays an important role in disarticulation and may ultimately control the process even following utilisation by predators and scavengers. The disarticulation sequence reported here has useful applications for the interpretation of fossil bone assemblages containing both extant and extinct kangaroos.

Long-term effects of warren ripping for rabbit control in semi-arid South Australia.

Warren ripping and poisoning were used to control rabbits on the flood-out plain of a major creek system on Manunda Station, a sheep-grazing property near Yunta in semi-arid South Australia. Rabbit numbers were initially reduced by &gt;99 per cent, as indicated by the number of active entrances remaining in rabbit warrens. After nearly 10 years without follow-up control work, ripped warrens had only two per cent of the pre-control number of active entrances. Poisoning effectively reduced rabbit numbers in the short-term, but had no long-term effect on the number of active entrances, either in ripped or unripped warrens. Perennial shrubs regenerated on and around ripped warrens. Warren ripping on this part of Manunda is a cost-effective management option.

Blade ploughs as an alternative to tined rippers for rabbit warren destruction in semi-arid areas.

A tractor-mounted blade plough was used to control rabbits in semi-arid South Australia by destroying their warrens. This implement was compared with a conventional two-tine ripper on the basis of effectiveness and cost. The blade plough was slightly less effective (overall mean 88% warrens destroyed) than the ripper (91% destroyed) three weeks after treatment but this difference was not significant. Warrens treated with the blade plough also had a slightly higher rate of reopening although the difference between treatments was not significant until 54 weeks after treatment. The blade plough was significantly faster in destroying warrens (mean 6.93 min cf. 9.88 min) despite frequent bogging of the tractor. The choice of a more suitable tractor should overcome this problem. Costs were similar but a small saving can be made by using a blade plough if a suitable tractor is already owned by the landholder. Including one follow-up treatment the cost of destruction per warren was $2.30 with the blade plough compared with $2.61 for the ripper. For properties where stock numbers are restricted, the return on an investment in rabbit control was estimated to be 13% per annum for the blade plough and 12% per annum for the ripper. Where stock numbers can be increased returns should be greater.

Practical and economic aspects of rabbit control in hilly semiarid South Australia

Poisoning, ripping of warrens and a combination of both techniques were assessed as means of controlling rabbits in steep areas of the southern Flinders Ranges in semiarid South Australia. The number of active warren entrances was reduced significantly by poisoning and by ripping. One month after treatment, untreated plots contained an average of 72.2 active entrances whereas the poisoned and ripped plots averaged 27.1 and 7.3 active entrances, respectively. A combination of both techniques reduced the number of active warren entrances even further, but this is not recommended because it increases the cost of control substantially. The efficiencies of a large and a small crawler tractor were compared. Costs of ripping were similar, and the suitability of each tractor is discussed. In the southern Flinders Ranges rabbit control is clearly economical in relation to the improvements in sheep production likely to be obtained.