Susan M. Carthew

Limited ecological connectivity of an arboreal marsupial across a forest/plantation landscape despite apparent resilience to fragmentation

Demographic and genetic replenishment of populations through the exchange of individuals is essential for their persistence. Habitat loss and fragmentation can reduce the permeability of landscapes, hinder dispersal and compromise the genetic integrity of populations over time. We examined ecological connectivity in an arboreal marsupial, the common ringtail possum (Pseudocheirus peregrinus) in fragmented forests of southeastern Australia. This species is potentially robust to fragmentation based on its presence in degraded landscapes and known use of plantations for foraging and nesting. Using 312 individuals screened at 15 microsatellites, we measured dispersal and gene flow across seven native Eucalyptus forest remnants surrounded by exotic Pinus radiata plantations and three sites within a large continuous forest. The permeability of the pine matrix to dispersing possums was significantly lower than that of the native forest. Small, isolated patches exhibited signatures of genetic drift, having lower heterozygosity and allelic richness than possums in large patches. Most (87%) possums were born in their sampled patch or dispersed only short distances into neighbouring remnants. The continuous forest was identified as an important source of immigrants only for proximate patches (within 2.5 km), thus emphasizing for the common ringtail possum and more specialized arboreal mammals the need to conserve large, proximate forest remnants. Our findings highlight the importance of using genetic tools to understand the long‐term biological consequences of fragmentation for effective management.

Molecular systematics and evolutionary origins of the genus Petaurus (Marsupialia: Petauridae) in Australia and New Guinea

The glider genus Petaurus comprises a group of arboreal and nocturnal marsupial species from New Guinea and Australia. Molecular data were generated in order to examine phylogenetic relationships among species within the genus and explore the time-scale of diversification and biogeographic history of the genus in Australia and New Guinea. All known species and subspecies of Petaurus (with the exception of P. biacensis) were sequenced for two mitochondrial genes (ND2 and ND4) and one nuclear marker (omega-globin gene). Phylogenetic analyses confirmed the monophyly of the genus relative to other petaurids and showed a sister relationship of P. australis to the rest of Petaurus. The analyses revealed that currently recognised species of Petaurus formed distinct mitochondrial DNA (mtDNA) clades. Considerable mtDNA diversity and seven distinct clades were identified within the species P. breviceps, with the distribution of each clade showing no correspondence with the distributional limits of known subspecies. Molecular dating analyses using BEAST suggested an early to mid-Miocene origin (18-24 mya) for the genus. Ancestral area reconstructions, using BayesTraits, did not resolve the location for the centre of origin of Petaurus, but provided evidence for at least one dispersal event from New Guinea to Australia that led to the evolution of extant Australian populations of P. breviceps, P. norfolcensis and P. gracilis. The timing of this dispersal event appears to pre-date the Pleistocene, adding to the growing number of studies that suggest faunal connections occurred between Australia and New Guinea in the Late Miocene to Pliocene period.

Conservation units and phylogeographic structure of an arboreal marsupial, the yellow-bellied glider (Petaurus australis)

Subspecific status has often been used as a surrogate for conservation unit, but does not always reflect intraspecific lineages with different evolutionary histories. One contentious case of subspecific classification occurs in the yellow-bellied glider (Petaurus australis), a marsupial species showing considerable decline in population size and requiring conservation management. Our aim was to assess the current subspecific status of populations and define units of conservation using a combination of phylogeographical analyses of mitochondrial DNA and morphological analyses. Analyses of the mitochondrial ND4 gene provided evidence for significant phylogeographic structure within P. australis. Isolated populations in north Queensland (NQ) and Victoria/South Australia were genetically distinct from populations in New South Wales and southern Queensland. Morphological analyses provided little evidence for discrimination of populations, although NQ specimens were generally smaller in size than southern forms. Our analyses do not support the classification of subspecies P. a. reginae for the original type specimen from southern Queensland. Taking into account other behavioural and ecological data, and the disjunct distribution of NQ populations from southern populations, we propose that the NQ population represents a distinct Evolutionarily Significant Unit, a lineage showing highly restricted gene flow from the rest of the species.

Use of space by the yellow-footed antechinus, Antechinus flavipes, in a fragmented landscape in South Australia

An understanding of how individual species are able to persist and move within fragmented landscapes is critical for elucidating the effects of fragmentation and aiding in the management of species. Here, we studied movement behaviour of the dasyurid Antechinus flavipes in a heavily fragmented landscape using trapping and radiotracking. We assessed the ability of animals to move within and amongst small (<6 ha) remnants and make use of the matrix, and investigated how females used the available space within remnants. Seventeen between-remnant movements were detected from 428 recaptures, ranging in length from 30 to 720 m and averaging 352 m. Most were by adult males during the breeding season, with 40% more than 500 m. Landscape types traversed would have included exotic pine plantations, open grazed areas and roads. Between-site movements of juveniles were only detected on three occasions. However, few young males were captured as adults, suggesting high dispersal rates and considerable matrix use. Conversely, despite high female recapture rates, again only three between-site movements were recorded. Radiotracking further indicated that females confined foraging to remnants, with occasional forays to isolated trees in paddocks. Female home range areas were similar for remnants and forest (0.04–0.66 ha). A. flavipes is clearly able to persist in very small patches of native vegetation in the landscape studied here. Its long-term persistence appears dependent on the ability of females to maintain a presence in the small remnants, and of unrelated males to move between remnants to breed with resident females. This study illustrates the importance of recognising the occurrence of metapopulations in fragmented landscapes for conservation management.

Diet of the bilby (Macrotis lagotis) in relation to substrate, fire and rainfall characteristics in the Tanami Desert

This study uses analysis of faecal pellets to assess the diet of the bilby (Macrotis lagotis) in an area spanning over 230 000 km2 in the Tanami Desert, Northern Territory. More specifically, we examine the link between diet composition, bilby prevalence and the landscape variables of fire, rainfall and substrate. Seed promoted by fire, particularly of Yakirra australiense, was found to be one of the most important components of the diet and constituted ~36% of the relative abundance of identifiable food particles. Bulb from Cyperus bulbosus was also an important component of the diet (18.5% relative abundance). Invertebrates accounted for 39% of the identifable food particles, and termites and beetles were the most common types. Bulb and seed formed a greater component of the diet in the central part of the study area where bilbies were more prevalent. Conversely, invertebrates were more dominant in the bilby diet on the northern and southern periphery of the Tanami Desert. Substrate type and antecedent rainfall associated significantly with the amount of seed from fire-promoted plants and total plant contained in the diet. Time since fire was an additional factor associated with the abundance of dietary fire-promoted seed. This suggests that the spatial and temporal variability of these landscape variables play an important role in controlling the availability of seed and bulb resources used by the bilby, and thus affect bilby prevalence. The results support the proposition that seed and bulb plant foods are exploited opportunistically and invertebrates, especially termites, are relied upon when plant food resources are scarce. Furthermore, the findings indicate that fire management could be used as a means to increase the favourability of habitat for the bilby in parts of its current range.

Population ecology of Ningaui yvonneae (Dasyuridae : Marsupialia) in the Middleback Ranges, Eyre Peninsula, South Australia

A population of the southern ningaui (Ningaui yvonneae) was studied in the semi-arid regions of South Australia. Data were collected on the population ecology of the species, including capture success, breeding biology and life history. Between August 1996 and December 1998, 307 captures were recorded from 11 016 trap-nights. Most individuals were caught only once and males were caught more frequently than females. Capture success varied greatly between seasons, with lowest captures being recorded in winter. Winter is a time of stress for N. yvonneae – mean weights stabilised between March and June. N. yvonneae is polyoestrous, with mating recorded from September to February. However, most matings took place in mid-October. The population was dominated by a single cohort, with the life span for N. yvonneae being approximately 14 months.

Post-fire ephemerals and spinifex-fuelled fires: a decision model for bilby habitat management in the Tanami Desert, Australia

Seed from post-fire ephemeral plants like Yakirra australiense can form an important component of the diet of the bilby, a threatened arid-dwelling bandicoot. An investigation was conducted to determine the factors affecting the production of Yakirra and fire reoccurrence in the Tanami Desert. A simple decision model was produced to assist managers decide where and when to burn and what to expect regarding Yakirra australiense growth following fire and rainfall. The information used in the model may be derived from existing spatial databases that document rainfall and fire history and could be used to map broad-scale temporal change in total vegetation cover and components of habitat suitability for the bilby. The season and magnitude of rainfall and time-since-fire were the most important variables in the production of Yakirra seed. Rainfall >300 mm within a 2-month period of intense-complete burns could result in >5% Yakirra cover, and >100 mm was required for >1% cover. Negligible Yakirra cover occurred in adjacent long-unburnt plots. Total ground cover and spinifex cover varied substantially in relation to mean annual rainfall, but not in relation to substrate type. Long-unburnt spinifex cover was mostly too sparse to carry a fire in the southern part of the Tanami and the growth of non-spinifex vegetation would be necessary to boost fuel loads sufficiently to carry a fire. Generally, more than 41% cover was required to carry a fire but this was also dependent on weather conditions. Managers should aim to burn in late spring or early summer to improve Yakirra production. Fire management to enhance habitat suitability for the bilby would be of most benefit in the northern part of the Tanami Desert where growth rate of vegetation is greater and there is little existing fire age heterogeneity.

Phylogeography of the Australian sugar glider (Petaurus breviceps): evidence for a new divergent lineage in eastern Australia

The sugar glider (Petaurus breviceps) shows considerable variation in external morphology and mitochondrial DNA (mtDNA) diversity across its distribution in New Guinea and Australia. Here we investigate the phylogeography of P. breviceps in Australia using data from two mitochondrial genes (ND2 and ND4) and a nuclear gene (ω-globin). Phylogenetic analyses revealed the existence of two divergent mtDNA clades that are distributed over distinct geographical regions, one from coastal New South Wales and south-eastern Queensland and a second over the remaining distributional range of the species in Australia. The two groups generally had distinct ω-globin haplotypes that differed by one or two mutational steps. Analyses of Molecular Variation further supported the presence of at least two populations, accounting for 84.8% of the total mtDNA variation and 44% of the ω-globin variation. The general concordance of phylogeographic and population analyses suggests that population subdivision, possibly resulting from the combined influences of aridification after the Pliocene and uplift of the Great Dividing Range has impacted the evolution of P. breviceps. Our results also show that the geographical distribution of the two evolutionary lineages does not correspond with the distribution of the current morphological subspecies and we further propose that they be considered as separate Evolutionarily Significant Units for the purposes of conservation management.

Microhabitat and vegetation structure preference: an example using southern brown bandicoots (Isoodon obesulus obesulus)

Abstract Improving our understanding of resources required by threatened small mammals is directly relevant to the success of habitat restoration and species reintroduction programs. In a case study based on southern brown bandicoots (Isoodon obesulus obesulus; Mammalia: Peramelidae) occupying a remnant of open forest with a sclerophyllous shrub understory, we investigated microhabitat composition using multivariate analysis, and disproportional use of these habitats using a variety of techniques, including principal canonical correlation vectors, chi-square test, compositional analysis (CA), and nonparametric multiplicative regression. Spool-and-line tracking of bandicoots enabled floristic and structural parameters to be recorded from sites of activity and compared with sites randomly located within 5-ha grids centered over each trapping transect. Each of the 4 methods applied contributed useful interrogation of the potential resources required by I. o. obesulus, with most disproportional use of microhabitats across activities detected using CA. Analyses supported fine-scale preference for Xanthorrhoea semiplana–dominated microhabitat across all activities, nesting in Banksia ornata–dominated microhabitat, moving and foraging in Allocasuarina muelleriana subsp. muelleriana microhabitat, impartial use of and increased reliance on burrows for shelter in Eucalyptus cosmophylla open forest with Melaleuca decussata understory microhabitats, and avoidance of Cyperaceae-dominated microhabitat and mixed heath. These results show that within broadly suitable vegetation communities, I. o. obesulus differentially utilizes a mosaic of microhabitats for a range of activities associated with shelter and foraging. Hence, the success of reintroduction and habitat restoration programs may be improved by considering the availability of preferred microhabitats (or alternative structures in suboptimal habitats, e.g., burrows), and protecting or revegetating indicator and associated species of known preferred microhabitats, respectively.

Roadside vegetation can provide valuable habitat for small, terrestrial fauna in South Australia

In some regions, extensive habitat clearance and fragmentation have largely restricted remnant vegetation to linear strips, often bordering roads and railway lines. Such areas may be important for the persistence of native wildlife but there is a paucity of research on their biodiversity value. This study in south-eastern South Australia compared the diversity and abundance of small, terrestrial animals in remnant vegetation, roadsides and farmland. Pitfall and Elliott trapping at 30 sites resulted in a total of 1,024 captures of 28 amphibian, reptile and mammal species, with 819 captures of six mammal species. Overall species diversity was highest in remnant sites and lowest in farm sites. Although low capture rates for reptiles and amphibians precluded statistical testing of individual species, many were caught in both remnant and roadside sites, but rarely at farm sites. Mammal captures consisted of four native (Cercartetus concinnus and C. lepidus, Pseudomys apodemoides and Rattus fuscipes) and two introduced (Mus musculus and Rattus rattus) species. Mus musculus was the most commonly caught species and was significantly more abundant in roadside than remnant vegetation. Abundance was negatively correlated with habitat quality and, at a finer scale, positively associated with percentage cover of exotic grasses. C. concinnus was also commonly captured; however, the absence of a difference in capture rates between remnant and roadside sites suggests that roadside vegetation provides important habitat. The abundance of C. concinnus was positively associated with percentage canopy cover. The current results highlight the conservation value of roadside vegetation and suggest that such areas should be both retained and appropriately managed.