Influence of interactive effects on long-term population trajectories in multispecies reintroductions

Reintroduced populations are typically considered to progress through establishment, growth, and regulatory phases. However, most reintroduction programs do not monitor intensively enough to test this conceptual model. We studied population indices derived from track activity of 4 threatened species (greater bilby [Macrotis lagotis], burrowing bettong [Bettongia lesueur], greater stick-nest rat [Leporillus conditor], and Shark Bay bandicoot [Perameles bougainville]) over 23 years after multiple reintroductions of each species in arid Australia. We compared population trajectories among species and investigated the effect of time and environmental variables. All species bred immediately after release, and the growth phase lasted 3-16 years, varying markedly among but not within species. The end of the growth phase was characterized by an obvious peak in population density followed by either a catastrophic decline and sustained low density (bettongs), a slow decline to extirpation after 20 years (stick-nest rat), or a slight decline followed by irregular fluctuations (bilby and bandicoot). Minor fluctuations were related to environmental variables, including 12-month cumulative rainfall and lagged summer maximum temperatures. Three of the 4 species did not reach a regulation phase, even after 23 years, possibly due to interspecific competition and trophic cascades triggered by predator removal and multispecies reintroductions. Bilbies and bandicoots exhibited a second growth phase 18 years after reintroduction, likely caused by high rainfall and increased resources following the population crash of overabundant bettongs. Our results suggest that assemblages within multispecies reintroductions demonstrate high variability in population trajectories due to interactive effects. Intensive monitoring to assess population viability may require decades, particularly where multiple species are reintroduced, release sites are confined, and the climate is unpredictable. Intensive monitoring also allows for adaptive management to prevent precipitous population declines. Practitioners should not assume reintroduced species pass through predictable postrelease population phases or that viability is assured after a certain period.

Haematology and serum biochemistry results for anaesthetised northern brown bandicoots (Isoodon macrourus) in south east Queensland

Bandicoots are terrestrial marsupials, endemic to Australia and Papua New Guinea. Despite drastic declines in several bandicoot species since European settlement, the northern brown bandicoot (Isoodon macrourus) remains common in many areas of Australia. It inhabits native environments as well as anthropogenic landscapes. This study presents comprehensive haematologic and serum biochemical results for 39 anaesthetised, clinically healthy, wild-caught, adult northern brown bandicoots in south east Queensland, Australia. The bloodwork profile of a single animal with chronic prostatic abscessation highlights that haematology and clinical chemistry can provide useful biomarkers for identifying clinical disease in bandicoots. Comparisons of haematologic and biochemical values between sexes of the northern brown bandicoot revealed significant differences for eosinophils, alkaline phosphatase and total bilirubin. At the individual animal level, the ranges established in this study are a guide for monitoring health and disease status; however, they also have much wider applications in population health and ecological research.

Managing ecosystems in a sea of uncertainty: invasive species management and assisted colonizations

Managing ecosystems in the face of complex species interactions, and the associated uncertainty, presents a considerable ecological challenge. Altering those interactions via actions such as invasive species management or conservation translocations can result in unintended consequences, supporting the need to be able to make more informed decisions in the face of this uncertainty. We demonstrate the utility of ecosystem models to reduce uncertainty and inform future ecosystem management. We use Phillip Island, Australia, as a case study to investigate the impacts of two invasive species management options and consider whether a critically endangered mammal is likely to establish a population in the presence of invasive species. Qualitative models are used to determine the effects of apex predator removal (feral cats) and invasive prey removal (rabbits, rats, and mice). We extend this approach using Ensemble Ecosystem Models to consider how suppression, rather than eradication influences the species community; and consider whether an introduction of the critically endangered eastern barred bandicoot is likely to be successful in the presence of invasive species. Our analysis revealed the potential for unintended outcomes associated with feral cat control operations, with rats and rabbits expected to increase in abundance. A strategy based on managing prey species appeared to have the most ecosystem-wide benefits, with rodent control showing more favorable responses than a rabbit control strategy. Eastern barred bandicoots were predicted to persist under all feral cat control levels (including no control). Managing ecosystems is a complex and imprecise process. However, qualitative modeling and ensemble ecosystem modeling address uncertainty and are capable of improving and optimizing management practices. Our analysis shows that the best conservation outcomes may not always be associated with the top-down control of apex predators, and land managers should think more broadly in relation to managing bottom-up processes as well. Challenges faced in continuing to conserve biodiversity mean new, bolder, conservation actions are needed. We suggest that endangered species are capable of surviving in the presence of feral cats, potentially opening the door for more conservation translocations.

Bioturbation by a reintroduced digging mammal reduces fuel loads in an urban reserve

Digging animals may alter many characteristics of their environment as they disrupt and modify the ground's surface by creating foraging pits or burrows. Extensive disturbance to the soil and litter layer changes litter distribution and availability, potentially altering fuel loads. In many landscapes, including peri-urban areas, fire management to reduce fuel loads is complex and challenging. The reintroduction of previously common digging animals, many of which are now threatened, may have the added benefit of reducing fuel loads. We experimentally examined how the reintroduction of a marsupial bandicoot, quenda (Isoodon fusciventer), altered surface fuel loads in an urban bush reserve in Perth, Western Australia. Foraging activities of quenda (where they dig for subterranean food) were substantial throughout the reserve, creating a visibly patchy distribution in surface litter. Further, in open plots where quenda had access, compared to fenced plots where quenda were excluded, quenda foraging significantly reduced litter cover and litter depth. Similarly, estimated surface fuel loads were nearly halved in open plots where quenda foraged compared to fenced plots where quenda were absent (3.6 cf. 6.4 Mg/ha). Fire behavior modeling, using the estimated surface fuel loads, indicated the predicted rate of spread of fire were significantly lower for open plots where quenda foraged compared to fenced plots under both low (29.2 cf. 51.4 m/h; total fuels) and high (74.3 cf. 130.4 m/h; total fuels) fire conditions. Although many environments require fire, including the bushland where this study occurred, fire management can be a considerable challenge in many landscapes, including urban bushland reserves, which are usually small and close to human infrastructure. The reintroduction of previously common digging species may have potential value as a complimentary tool for reducing fuel loads, and potentially, fire risk.

Elucidating Patterns in the Occurrence of Threatened Ground-Dwelling Marsupials Using Camera-Traps

Simple Summary

Being able to effectively monitor the continued plight of highly vulnerable animals against management efforts over time is critical for their conservation. In south-eastern New South Wales, Australia, we used a camera trapping array to collect baseline information about patterns of occurrence of three threatened native ground-dwelling marsupials of conservation interest: the long-nosed bandicoot (Perameles nasuta), long-nosed potoroo (Potorous tridactylus) and southern brown bandicoot (Isoodon obesulus). Over a four-year period, detections of the two bandicoots were more erratic and less predictable than that of the potoroo, resulting in higher uncertainty about occupancy estimates and adequacy of sampling effort. The detection probability of each bandicoot species and that of the potoroo differed variously with structural complexity of vegetation. Detection probability of the southern brown bandicoot was highest where ground cover was most dense and shrub cover most open. The reverse pattern was found for the long-nosed bandicoot. Finally, the detection probability of the long-nosed potoroo was highest where ground and shrub cover was densest. Future camera trapping monitoring efforts need to take better account of these nuances and be flexible to including additional sampling for at least the two bandicoots. In short, when it comes to monitoring approach, one size doesn’t fit all.

Abstract

Establishing trends in endangered fauna against management efforts is a key but often challenging enterprise. Camera-traps offer a new and literal window into monitoring many different mammalian species. Getting it right demands seeking baseline information about how often target species interact with these devices, prior to setting a long-term monitoring strategy. We used a camera-trap array to collect detection data on three species of threatened ground-dwelling marsupials in south-eastern mainland Australia. Over a four-year period, occupancy estimates for two species of bandicoot (southern brown bandicoot Isoodon obesulus and long-nosed bandicoot Perameles nasuta) and a single species of rat-kangaroo (long-nosed potoroo Potorous tridatylus) were generated. These estimates were variously robust depending on visitation history, but nevertheless indicated persistence of these rare and otherwise under threat species. Detection probability for each species differed between study areas, type of management and with complexity of ground and shrub vegetation cover. The relationship between detection and vegetation structure dictated that survey effort was only robust where conditions were optimal for a given species. Outside of that further survey effort would be required to have confidence in survey outcome. In the future this would demand a different sampling strategy, be that through lengthening survey time or adding additional camera units at sites.

Mycobacterium ulcerans DNA in Bandicoot Excreta in Buruli Ulcer-Endemic Area, Northern Queensland, Australia

To identify potential reservoirs/vectors of Mycobacterium ulcerans in northern Queensland, Australia, we analyzed environmental samples collected from the Daintree River catchment area, to which Buruli ulcer is endemic, and adjacent coastal lowlands by species-specific PCR. We detected M. ulcerans DNA in soil, mosquitoes, and excreta of bandicoots, which are small terrestrial marsupials.

A framework for developing and validating taxon-specific primers for specimen identification from environmental DNA

Taxon-specific DNA tests are applied to many ecological and management questions, increasingly using environmental DNA (eDNA). eDNA facilitates noninvasive ecological studies but introduces additional risks of bias and error. For effective application, PCR primers must be developed for each taxon and validated in each system. We outline a nine step framework for the development and validation of taxon-specific primers for eDNA analysis in ecological studies, involving reference database construction, phylogenetic evaluation of the target gene, primer design, primer evaluation in silico, and laboratory evaluation of primer specificity, sensitivity and utility. Our framework makes possible a rigorous evaluation of likely sources of error. The first five steps can be conducted relatively rapidly and (where reference DNA sequences are available) require minimal laboratory resources, enabling assessment of primer suitability before investing in further work. Steps six to eight require more costly laboratory analyses but are essential to evaluate risks of false-positive and false-negative results, while step 9 relates to field implementation. As an example, we have developed and evaluated primers to specifically amplify part of the mitochondrial ND2 gene from Australian bandicoots. If adopted during the early stages of primer development, our framework will facilitate large-scale implementation of well-designed DNA tests to detect specific wildlife from eDNA samples. This will provide researchers and managers with an understanding of the strengths and limitations of their data and the conclusions that can be drawn from them.