That the brushtail possum was once common and widespread in the arid zone is confirmed by a collation of historical information. Although possums were widespread, detailed records from the Northern Territory and South Australia show that they were most abundant in rocky ranges and outcrops and along watercourses. Possums are now rare in the arid zone. In considering the reasons for the decline of this apparently robust species we have further developed Morton's (1990) model for mammal decline in the arid zone. Our hypothesis is based on the premise that disturbance of refuge habitat patches critical for the survival of the species was occurring at the same time as the country was subjected to a below average water balance. During the period between 1920 and 1970 rainfall was either average or markedly below average with no exceptional rainfalls recorded. Analysis of the rainfall data using a cumulative residual mass curve suggests that sub-surface waters were probably not fully recharged, placing a natural stress on the refuge habitats. At the same time, possum populations were being affected by many disturbing factors introduced by European settlement. Once the populations were reduced, they fell into a 'predator- pit' through depredation by dingoes and introduced predators and were unable to increase in numbers even with the advent of improved conditions. In this paper we identify the need to accurately determine the refuge habitats of a species and then utilise tools such as the cumulative mass residual curve to predict when these habitats will be under most stress. Specific protection measures can then be developed in association with land managers in order to reduce disturbance at the most critical times.
The population ecology of Trichosurus vulpecula has been studied extensively in temperate Australia and in New Zealand. This paper provides the results of a trapping study of a population of the northern brushtail possum (T. vulpecula arnhemensis Collett 1897) in the wet–dry tropics of Australia’s Northern Territory. Possums were readily trapped and the population had a comparatively high density for Australian brushtails of around 3 per hectare. The core home-range size and range length for males was 1.12 ha and 165 m; this was a little larger than for females (0.89 ha and 155 m). The possums were not very agressive when handled and were apparently quite socially tolerant. The ready availability of nutritious food sources throughout the year enables them to breed continuously, producing 1.7 young per year per adult female. If environmental conditions become unfavourable with a series of poor wet seasons or frequent fires, the habitat will resemble the less-productive eucalypt forest not occupied by possums. Mortality of pouch young and immatures will increase under these conditions but with a potential reproductive rate of nearly two per year, populations of the northern brushtail can readily recover from short periods of unfavourable conditions.
The taxonomic status of distinctive populations of the widespread and morphologically variable possum Trichosurus vulpecula was examined. For the analysis, morphological characters (body size, fur colour and skull dimensions), karyotypes, electrophoretic allozyme, and ecological data were compared for as many Trichosurus populations as possible. There are insufficient differences between populations of T. vulpecula to reject a null hypothesis that they comprise a single species. Tasmanian, northern and south-western Australian populations could be retained as subspecies, but insufficient data exist to resolve the specific status of Atheton Tabeland and north-eastern Australian populations. One enigmatic result is that the skull morphometrics and allozymes of T. caninus were not distinguishable from those of sympatric T. vulpecula. However, other morphological characteristics and ecological data provide adequate evidence the T. caninus is a distinct species.
On the Pancontinental Jabiluka exploration lease, between July 1979 and September 1981, mammals of 30 native and five introduced species were recorded, with an overall trap success rate of 5% and an average of 1.9 sightings per spotlight-hour. Three major groups of mammal species corresponded to the primary groupings of vegetation in the study area: riparian woodland, dryland woodland and open forest, and sandstone. This last group was subdivided into three on site preferences. Two ungrouped species were found in a variety of habitats. The distribution of mammals was very patchy, and their abundance varied seasonally. This may result from rainfall patterns, fire occurrence and fire history, as well as from landform and edaphic factors. The species responded to the variation in environment and the consequent mosaic of habitats by three strategies: by rapid response to changes in microhabitat through increased dispersion or moving to more favourable habitats, by restriction to stable habitats, or by adaptation to a variety of habitats.
The breeding biology of Trichosurus vulpecula has been studied in some detail for temperate populations but not for the northern brushtail possum (T. v. arnhemensis), the tropical form of this species. Data for the distribution of births and sex ratio of the young, growth and development of the young and reproductive cycles of both males and females were obtained. Most data were collected from a captive breeding colony of northern brushtails and supplemented with data from wild populations. The reproduction, growth and development of T. v. arnhemensis are very similar to those already described for other populations of T vulpecula. The observed differences can be explained by variation in the size of the animals and the absence of a restricted breeding season. Neither males nor females showed any periodicity in their reproductive strategy. This continuous breeding cycle can be attributed directly to their tropical environment. These tropical possums occupy a stable habitat, mature early and have a higher reproductive effort than populations in more seasonal and unpredictable environments. This suggests that the northern brushtail has a stochastic or 'bet-hedging' reproductive strategy.
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