Density estimates reveal that fragmented landscapes provide important habitat for conserving an endangered mesopredator, the spotted-tailed quoll

Native predators are increasingly exposed to habitat loss and fragmentation globally. When developing conservation and management strategies, it is important to determine whether fragmented landscapes can still support similar predator densities to intact areas, and thereby constitute important habitat for these species. The spotted-tailed quoll (Dasyurus maculatus) is an endangered Australian mesopredator that is often considered to be forest-dependent. While quolls are known to occur in some fragmented forest landscapes, it is unclear whether these areas represent sub-optimal habitat where quolls merely persist, or whether quolls can still occur at densities similar to those observed in intact forest landscapes. We used camera traps to detect quolls in both a fragmented and intact forested site, over three years. We used each quoll’s unique pelage pattern to identify individual quolls and estimate population density at each site. We were able to assign more than 94% of quoll image sequences across both sites to identify 173 individuals during the study. Density estimates of 0.13–0.66 quolls per km² at the fragmented site were comparable to estimates of 0.28–0.48 quolls per km² at the intact site. Our results highlight the importance of retaining and protecting forest fragments for the conservation of endangered quoll populations.

Recent decline of an endangered, endemic rodent: does exclusion of disturbance play a role for Hastings River mouse (Pseudomys oralis)?

Context The role of disturbance and its exclusion is fundamental to the conservation of threatened species. Aims We used the habitat accommodation model as a framework to investigate the importance of forest disturbance for the endangered Hastings River mouse, Pseudomys oralis, focusing on timber harvesting. Methods Our study comprised two separate surveys. We resurveyed old survey sites (n = 24) where the species was originally recorded as either present (logging excluded) or absent (subsequently logged). A second survey targeted trapping in high-quality habitat stratified by different times since logging. Finally, we analysed a 15-year trapping dataset targeting P. oralis to assess associations with co-occurring species. Key results The resurvey of old sites resulted in 12 P. oralis individuals being trapped, compared with 46 individuals in original surveys. Substantial declines were observed over time in transects where logging was excluded (60–82% decline), whereas there was little change at transects where P. oralis was not previously trapped and that were subsequently logged. The second survey yielded 27 P. oralis captures at post-logging sites assessed as high quality. Occupancy was very high (ψ = 0.93 ± 0.21) in transects logged 7–15 years ago and was 60% less in transects where logging was excluded for 35–45 years (ψ = 0.37 ± 0.22), whereas occupancy in transects logged 2–6 years ago was intermediate. This pattern of higher occupancy in logged areas was mirrored for the mean number of P. oralis trapped per transect. Ordination of habitat data showed an association of P. oralis with heath, mat-rushes and logs, whereas rats (Rattus and Melomys) were associated with ferns and shrubs. Camera traps revealed low background levels of predator presence. A negative exponential relationship was found between probability of occupancy of P. oralis and rat abundance from a 15-year trapping dataset (44 275 trap-nights), suggesting that rats may compete with P. oralis. Conclusions Our results supported the habitat accommodation model and suggested that disturbance is likely to influence the persistence of P. oralis. However, an interaction between predation and loss of cover from high-frequency disturbance (fire or intense grazing) cannot be excluded as a key threat. Implications Disturbance should be incorporated into the management of some species. Adaptive monitoring is recommended to assess alternative management regimes.

When the ‘native cat’ would ‘plague’: historical hyperabundance in the quoll (Marsupialia : Dasyuridae) and an assessment of the role of disease, cats and foxes in its curtailment

Since the European settlement of Australia in 1788, 25 mainland terrestrial mammal species have become extinct, more than on any other continent during this period. To determine if the causal factors are still active, it is necessary to better understand the species and their status preceding these regional extirpations or extinctions, and examine the historical record for clues to the cause(s) of these declines. From an extensive review of historical material, primarily newspaper accounts, we collated >2700 accounts of quolls. We discovered 36 accounts that demonstrate the propensity for quolls to become hyperabundant. The geographical distribution of accounts implies that most refer to Dasyurus viverrinus, but an account from Normanton district (Queensland) likely applies to D. hallucatus. More than 110 accounts demonstrate that disease/parasite epizootics occurred in south-eastern Australia, commencing on mainland Australia possibly in the goldfields region of Victoria in the 1850s, or in south-eastern South Australia and south-western Victoria in the mid to late 1860s, and implicate these as the initial primary factor in the regional extirpation of Australia’s quolls. The loss of D. viverrinus populations in south-eastern Australia was reportedly from population abundances and densities that were sporadically extraordinarily high, hence their loss appears more pronounced than previously suspected. Accounts describing the widespread, rapid and major loss of quolls suggest the possible involvement of several pathogens. Ectoparasites such as Uropsylla tasmanica and ticks appear to be described in detail in some accounts. A few others state comortality of Felis catus and Canis lupus familiaris, suggestive of a disease of either or both of these species, such as Canine Distemper Virus, a morbillivirus with a propensity to be non-host specific, that may have caused the decline of the quolls, perhaps vectored by the reported ectoparasites. We also collated 23 presumed independent accounts of cats negatively impacting quolls, two of which describe significant mortality, and three presumed independent accounts of fox predation. These highlight the capacity of both of these introduced predators to have reduced quoll distribution and abundance.

Population viability analysis shows spotted-tailed quolls may be vulnerable to competition

Competition between carnivores can strongly affect their behaviour, abundance and distribution. Recent analyses suggest a strong likelihood of competition between eutherian predators and the endangered spotted-tailed quoll (Dasyurus maculatus), although experiments are required to confirm this. If competition does occur, what are its likely effects on the long-term survival of spotted-tailed quoll populations? We used population viability analysis (PVA) to predict the fate of a hypothetical quoll population under various scenarios of competition. PVA showed that spotted-tailed quoll populations may be susceptible to extinction when faced with high densities of competitors. Model scenarios simulating exploitation competition and/or intraguild killing greatly reduced the population’s probability of survival, leading in the worst-case scenario to almost certain extinction.

Top predators as biodiversity regulators: the dingo Canis lupus dingo as a case study

Top-order predators often have positive effects on biological diversity owing to their key functional roles in regulating trophic cascades and other ecological processes. Their loss has been identified as a major factor contributing to the decline of biodiversity in both aquatic and terrestrial systems. Consequently, restoring and maintaining the ecological function of top predators is a critical global imperative. Here we review studies of the ecological effects of the dingo Canis lupus dingo, Australia's largest land predator, using this as a case study to explore the influence of a top predator on biodiversity at a continental scale. The dingo was introduced to Australia by people at least 3500 years ago and has an ambiguous status owing to its brief history on the continent, its adverse impacts on livestock production and its role as an ecosystem architect. A large body of research now indicates that dingoes regulate ecological cascades, particularly in arid Australia, and that the removal of dingoes results in an increase in the abundances and impacts of herbivores and invasive mesopredators, most notably the red fox Vulpes vulpes. The loss of dingoes has been linked to widespread losses of small and medium-sized native mammals, the depletion of plant biomass due to the effects of irrupting herbivore populations and increased predation rates by red foxes. We outline a suite of conceptual models to describe the effects of dingoes on vertebrate populations across different Australian environments. Finally, we discuss key issues that require consideration or warrant research before the ecological effects of dingoes can be incorporated formally into biodiversity conservation programs.