Harriet Mills

Conservation significance of island versus mainland populations: a case study of dibblers (Parantechinus apicalis) in Western Australia

Island populations are an interesting dichotomy in conservation biology. On the one hand, they can be a refuge for species where mainland populations have been decimated by loss of habitat and predation by exotic predators. On the other hand, island populations usually have reduced genetic diversity and are more susceptible to extinction through genetic and demographic processes. Genetic variation and morphological characters were measured for island and mainland populations of Parantechinus apicalis, small dasyurid marsupials, restricted to southwest Australia. Genetic variation at seven microsatellite loci revealed low levels of heterozygosity (He = 0.20 - 0.44) and high levels of inbreeding (Fe = 0.40 - 0.72) in island populations compared with the mainland population (He = 0.73). A nested clade analysis revealed that allopatric fragmentation was probably responsible for the association between geographical location and control region haplotypes, which is consistent with the isolation of populations on islands and indicative of two main populations of P. apicalis representing separate conservation units for management. While these results are typical of many island populations, they have important implications in terms of the conservation of threatened species in Australia and around the world, where island populations are a common source of founders for captive breeding and translocation to mainland sites.

Offspring sex varies with maternal investment ability: empirical demonstration based on cross-fostering

Despite decades of interest, adaptive explanations for biased offspring sex ratios in mammals remain contentious, largely because direct tests of the underlying fitness assumptions of adaptive hypotheses are rarely conducted. These tests are complicated by the difficulty of manipulating offspring sex prior to significant maternal investment owing to the biological constraints of viviparity. We test the adaptive advantage of sex allocation through cross-fostering offspring by sex in tammar wallabies. We examine whether offspring sex is correlated with maternal investment ability (i.e. Trivers–Willard hypothesis, TWH). In addition, we test the assumption that maternal investment has a greater influence on the fitness of sons than of daughters. We failed to find statistical support for maternal investment ability influencing a sons weaning success or body size more than a daughters, although this result was probably owing to small sample sizes. In support of the TWH, females that gave birth to a son had higher investment ability (likelihood of weaning an offspring) regardless of the sex of offspring fostered.

New evidence for facultative male die-off in island populations of dibblers, Parantechinus apicalis

The post-mating mortality of males in dasyurid species is thought to be a specific life-history strategy, associated with a tightly synchronised breeding season, that may enhance survivorship of juveniles. Parantechinus apicalis has been reported to exhibit male die-off in island populations but not in mainland populations, and males originating from both island and mainland populations are known to survive post-mating in captivity. However, males in the island populations have been reported to sometimes survive to breed in a second year. This study monitored captive and island populations over a three-year period (April 1997 – May 2000) to examine the extent of male die-off. In captivity, males showed no evidence of post-mating mortality. Males on one island were also found to survive post-mating, while another island population appeared to have high mortality of males in three years, and a complete male die-off after the 1999 breeding season. We conclude that P. apicalis may warrant inclusion in a new category of life-history strategy for species exhibiting facultative male die-off.

Multiple individual southern brown bandicoots (Isoodon obesulus fusciventer) and foxes (Vulpes vulpes) use underpasses installed at a new highway in Perth, Western Australia

Context. Although wildlife crossing structures are often included when new roads are built, their effectiveness at reconnecting wildlife populations is still largely unknown. A new highway was built in 2005 through an area of remnant vegetation in Perth, Western Australia. Assessment of the area before construction identified potential impacts on a population of southern brown bandicoots (Isoodon obesulus fusciventer). Aims. We aimed to determine the use by bandicoots of three underpasses constructed to provide a linkage between habitats that were fragmented by the highway, focussing on how many different individuals used them, which is an essential step to demonstrate their effectiveness at reconnecting fragmented populations. Methods. We used detection of tracks in sand pads for 1 year to establish the use of the underpasses by bandicoots. We then captured 56 bandicoots and fitted them with passive integrated transponders (PIT), and installed a Trovan 650 scanner/decoder within the most frequently used underpass to establish whether multiple individuals used it. Key results. By using sand pads, we demonstrated that bandicoots used the underpasses, with a total of 278 passes between August 2005 and August 2006. One underpass accounted for 71% of these passes and was used already during construction. Eight different bandicoots were recorded using this underpass between August 2006 and August 2007, demonstrating use by multiple individuals. A dramatic decline in the use of this underpass was observed after foxes (Vulpes vulpes) also started using it in August 2006, and a fox built a den near the entrance of this structure. Because we also failed to recapture any of the bandicoots implanted with PITs we suspect that they had been killed by foxes. Conclusions. A severe decline in bandicoots coinciding with underpass use by foxes raises questions as to the long-term success of fauna crossings. Clearly, the relationship between underpass use by predators and the target species, in this case bandicoots, needs to be examined further. Implications. Our work demonstrated that although underpasses have the potential to reconnect populations because multiple individuals used them, their installation may be detrimental to wildlife populations if predators are not controlled.

Increasing the target-specificity of ERADICAT® for feral cat (Felis catus) control by encapsulating a toxicant

ERADICAT®, a sausage-type meat bait, has been developed for use in managing feral cat (Felis catus) populations throughout Western Australia. However, concern about potential exposure of non-target species to bait-delivered toxicants has led to the development of a technique to more specifically target feral cats using a pellet. Research into the consumption, by cats and native animals, of toxic pellets implanted within the ERADICAT® bait has been simulated using ball bearings as a substitute pellet. Results from our work indicate that encapsulating the toxicant may pose less risk of poisoning to chuditch (Dasyurus geoffroii), woylies (Bettongia pencillata) and southern brown bandicoots (Isoodon obesulus) as they consumed significantly fewer ball bearings (P = 0.003, <0.001, <0.001) than semi-feral cats (P = 0.07). Theoretically, a toxic pellet will not reduce the effectiveness of the ERADICAT® bait as there was no significant difference between consumption of baits and the consumption of ball bearings in feral cats (P = 0.07). Therefore, baits containing a toxic pellet have the potential to be a more selective method to control feral cats.

Deslorelin implants control fertility in urban brushtail possums (Trichosurus vulpecula) without negatively influencing their body-condition index

Wild brushtail possums (Trichosurus vulpecula) occur in large numbers in the grounds of Perth Zoo, Western Australia. These possums are a problem because they consume feed the zoo buys for its captive animals, damage seedlings and trees and many need to be treated for injuries sustained during fights with conspecifics. A contraceptive implant, which contains the gonadotrophin releasing hormone (GnRH) agonist deslorelin, could be a potential method of managing this population. We tested the efficacy of the implant and its impact on the body-condition index of treated possums with Kaplan–Meier analysis and a mixed model with residual maximum likelihood. We implanted 60 female possums with deslorelin and monitored reproductive success of treated and untreated possums for the following 18 months. At the conclusion of the study, 80% of 20 treated females recaptured had shown no evidence of breeding activity, giving an average minimum duration of effective contraception of 381 days. The implant did not have a negative impact on the body-condition index of treated possums during the course of the study. Our results suggest that deslorelin implants could be an effective management tool for brushtail possums at Perth Zoo and in other urban environments.

Habitat and diet of the dibbler (Parantechinus apicalis) on two islands in Jurien Bay, Western Australia

Trapping was conducted over three years on Boullanger and Whitlock Islands in Jurien Bay (Western Australia), to establish the habitat and diet of the dibbler (Parantechinus apicalis), an endangered marsupial. Habitat preference was determined by conducting a single-factor ANOVA of the trapping success rate for P. apicalis captured at each trap site. The diet was investigated by scat analysis. On Boullanger Island there was no significant difference between trapping success rate in the different habitats. However, on Whitlock Island, significantly greater trapping success rates were recorded in the dunal scrubland dominated by Nitraria billardierei and foredune heath than in succulent heath. Scats contained arthropod (65%) and some vegetable (25%) matter, confirming that island P. apicalis are chiefly insectivorous and rarely eat vertebrate prey.

Food availability for the dibbler (Parantechinus apicalis) on Boullanger and Whitlock Islands, Western Australia

The aim of this study was to assess food availability for the dibbler (Parantechinus apicalis) on Boullanger and Whitlock Islands in different habitats and seasons. This was assessed by capturing ground-dwelling invertebrates in pitfall traps in winter, spring and autumn. A quantitative faecal-pellet analysis was conducted to determine the composition of the diet. There were no significant differences in the number of invertebrates captured in the different seasons, or in the different habitat types on the islands. The proportion of plant versus animal matter in the faecal pellets did not change significantly between the seasons. The diet consisted of ~20% plant material. The scat analysis showed that dibblers consumed at least 10 orders of invertebrates ranging in length from 0.1 mm to 25 mm with an average size of 4.5 ± 0.4 mm. The dibblers did not select for a particular size or taxon of prey, but fed on any invertebrates that were readily available to them. This suggests that dibblers are essentially insectivorous dietary generalists and opportunists. The information gathered in this study could be applied when considering available food resources at future translocation sites for dibblers.

Spatial and dietary requirements of the chuditch (Dasyurus geoffroii) in a semiarid climatic zone

Knowledge of the ecology of the chuditch (Dasyurus geoffroii) is largely restricted to its distribution in mesic jarrah forests. There is a need for information regarding its ecology in semiarid zones where rainfall and consequently productivity are lower than mesic forests. Given that spatial requirements are strongly influenced by resource availability, it was expected that the chuditch in the semiarid zone would be present at lower densities and would have larger core home ranges (defined by daytime refuges) than those in the jarrah forests. The diet was also investigated by examining the contents of scats. Chuditch at Forrestania were trapped and six individuals were radio-tracked. The population density was one-third that of the lowest estimate reported from the jarrah forest and core home-range estimates were substantially larger, particularly for males. The diet included mammals, birds, reptiles, invertebrates, plants and rubbish, which was consistent with it being a generalist predator. Chuditch did have greater spatial requirements than in the jarrah forest, therefore different management regimes may be needed for populations occurring in the semiarid zone.

Temporal patterns in the abundance of a critically endangered marsupial relates to disturbance by roads and agriculture

The aim of this study was to investigate how landscape disturbance associated with roads, agriculture and forestry influenced temporal patterns in woylie (Bettongia penicillata) abundance before, during and after periods of rapid population change. Data were collected from an area of approximately 140,000 ha of forest within the Upper Warren region in south-western Australia. Woylie abundance was measured using cage trapping at 22 grid and five transect locations with varying degrees of landscape disturbance between 1994 and 2012. We found evidence that the distribution and abundance of woylies over time appears to be related to the degree of fragmentation by roads and proximity to agriculture. Sites furthest from agriculture supported a greater abundance of woylies and had slower rates of population decline. Sites with fewer roads had a greater abundance of woylies generally and a greater rate of increase in abundance after the implementation of invasive predator control. The results of this study suggest that landscape disturbance is less important at peak population densities, but during times of environmental and population change, sites less dissected by roads and agriculture better support woylie populations. This may be due to the role these factors play in increasing the vulnerability of woylies to introduced predators, population fragmentation, weed species invasion, mortality from road collisions or a reduction in available habitat. Strategies that reduce the impact of disturbance on woylie populations could include the rationalisation of forest tracks and consolidation of contiguous habitat through the acquisition of private property. Reducing the impact of disturbance in the Upper Warren region could improve the resilience of this critically important woylie population during future environmental change.