Thesis
The ecology of the Hastings River mouse Pseudomys oralis (Rodentia: Muridae) in Northeastern New South Wales and Southeastern Queensland
Southern Cross University, School of Environmental Science and Management
Doctor of Philosophy (PhD), Southern Cross University
2000
Metrics
124 File views/ downloads
311 Record Views
Abstract
Fossil and subfossil records of Hastings River Mouse Pseudomys oralis are distributed through eastern Victoria and much of eastern New South Wales. Some of the subfossils appear to be relatively recent in age, even to the point of co-occurring with introduced species. Pseudomys oralis is plentiful in several deposits and has survived climatic fluctuations through the Pleistocene and Holocene. As a modern species, P. oralis is much more limited in distribution and there are few records of individuals or populations. Accordingly, it is listed on Commonwealth and State (NSW) legislation as an endangered species.
In order to determine the range of management options needed to conserve the species, an understanding of the species' ecology and social organisation is essential. Prior to the present study, very little was known of the field biology of the species, as most capture sites have yielded single animals or very small groups, and there had been no temporal studies. The aim of this project was to undertake a long-term field study of aspects of P. oralis biology, specifically breeding biology, social organisation and diet. A secondary aim was to examine the evolutionary history of the Pseudomys to elucidate the historical status of the genus as well as the species. A further aim was to review and collate information from all other Pseudomys as a basis for broad predictions concerning aspects of P. oralis biology which could not be studied in the field. Information on the life history, social organisation and diet of contemporary P. oralis populations is presented, and the broad historical and evolutionary niche of the species is described.
Pseudomys oralis belongs to an aggregate of species of which about half have undergone demonstrable range reduction. The species which have suffered a similar geographical pattern of reduction to P. oralis also share certain habitat characteristics as well as large body form and other ecological similarities.
Two populations were studied in the field; one in northeastern New South Wales and one in southeastern Queensland. Most of the data come from these two sites. Additionally several other areas were surveyed by trapping. The populations at the two main sites revealed differences in demography. The Queensland site, Gambubal, was characterised by an abundant, relatively high-density population where population turnover was relatively high. Juvenile mortality was low and recruitment of subadults was high. Survival rates of adults declined over winter, with few surviving to breed a second season. The New South Wales site, Billilimbra, was more typical of previously reported abundance levels in that it was very low. However, animals had high survival rates and tended to remain on the grid for long periods (up to two years). Adult mortality was low and a high proportion survived to breed in a second season. Changes in the demography of both populations appeared to be strongly influenced by any changes in the number of adult females present.
Breeding patterns were broadly similar at the two sites, although timing of reproductive season varied between sites and between years. Pseudomys oralis commenced breeding between August and October. Last matings were thought to occur in February, with latest born young weaned by April. Females were thought to be capable of producing between one and three litters per season. Older females are likely to have more and larger litters than younger females. Litter size is between one and four, with an average between two and three. Animals of either sex did not breed until they were approximately one year old. At the transition from subadult to breeding adult status, animals had attained approximately 90% of mean adult weight and head-body length.
Growth was thought to be multi-phasic, with rapid initial growth from juvenile to subadult state. Growth slowed from subadult to adulthood, then slowed again as animals continued to gain weight into their second year as adults. Pseudomys oralis lived up to three years, with females possibly surviving longer than males.
The differences in life history and demography between the two populations were examined in relation to life history theory. Some traits were variable between sites, for example abundance and density, adult:juvenile mortality rates, survival and residency times. Other traits were similar for both populations, i.e. growth, litter size. Gambubal appeared to have a greater carrying capacity than Billilimbra and a higher turnover rate allowed for new individuals to constantly enter the population. Billilimbra had a lower carrying capacity, but high survival rates and long persistence times of individuals. Thus, the Billilimbra population remained very stable between years and seasons.
Social organisation and movement patterns were investigated by radiotracking. Males had significantly larger home ranges than females at both sites, and home range sizes were similar between sites. Core areas of both sexes were similar, although variable. Animals at Gambubal overlapped with more conspecifics than animals at Billilimbra, and males overlapped with more conspecifics than females at both sites. Many adults showed strong site fidelity. Males moved further than females, both as a total of intra-night inter-fix distance and as the distance between successive trapping points. No clumping was detected in the dispersion of animals at either site.
The mechanisms of dispersal appeared to be multiple, with some evidence of philopatry, some evidence of dispersal of young animals of both sexes (probably juvenile-male dominated) and some evidence of adult females "bequeathing" territory to offspring. Juveniles which disperse were thought to do so at around four to five months. The factors which influence the types of dispersal are unknown. The social organisation seems to consist of a dispersed group of animals living singly, apart from brief periods connected with mating, and cohabitation of mother and offspring groups. Each adult maintains a core area and peripheral territory, although nothing is known of the behavioural mechanisms which enforce them. In a high-density population, there may be more overlap of range than in a low density population.
The diet of P. oralis was studied by means of faecal analysis using scats from three sites. Distinct seasonal differences were found within populations. In general, mice ate a higher proportion of leaf material in winter and increased seed consumption in spring and summer. Monocotyledonous material was used more by Gambubal animals and dicotyledenous material was more prevalent at Billilimbra. In addition, mice ate fruit, moss, fungi and insects. Although the pattern of seasonal variation was broadly similar, there were differences in proportions of each food group consumed. However, many of the plant species eaten, including some grass species and leguminous herbs, were common to all sites and may constitute an important aspect of habitat selection and suitability. Pseudomys oralis appears to be a generalist herbivore/omnivore able to exploit a variety of different food sources. This finding agrees with prior studies of P. oralis diet and is not dissimilar to results of dietary studies of other Pseudomys species.
Habitat at the study sites was described in terms of structural and floristic measures taken at each trap site. There was correlation between the amount of shelter sites, the amount of food plants and structural complexity and trap success. Floristic assemblages at all sites were broadly similar. Potential shelter sites were more abundant at Gambubal and some food plants were also more abundant. It is hypothesised that the abundant shelter availability at Gambubal allows a higher population to exist.
The small mammal fauna which co-existed with P. oralis was diverse and in some cases, abundant. Factors which are important for P. oralis habitat such as site productivity, shelter availability and low predation rates may also be important for other small mammals species. Community structure and habitat preferences of small mammals in this bioregion appear to be more complex than previously thought.
Pseudomys oralis occupies a narrow band of habitat within the region of overlap between the tropical and temperate zones. The habitat is defined by precipitation level and seasonality, soil type, aspect, elevation vegetation and fire history. The habitat is fairly stable, with periodic fires. The stability of the populations, low rates of reproduction high site-fidelity of individuals and limited dispersal ability suggest that P. oralis is adapted to a stable environment. The perennial nature of the major food source also suggests stability of habitat.
The findings of this study have implications for conservation and management of the species, and have been incorporated into a Recovery Plan.
Details
- Title
- The ecology of the Hastings River mouse Pseudomys oralis (Rodentia: Muridae) in Northeastern New South Wales and Southeastern Queensland
- Creators
- Sally Jane Townley
- Contributors
- Peter Baverstock (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University, School of Environmental Science and Management
- Number of pages
- xviii, 287
- Identifiers
- 991012957298902368
- Copyright
- © Sally J. Townley 2000
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis