The occurrence, relative abundance and environmental associations of small terrestrial mammals in the Northern Kimberley, Western Australia

Abstract

This study examines the distribution and abundance of the small terrestrial mammal fauna (non-volant, <2kg) in the Northern Kimberley bioregion, Western Australia. This region is considered ‘pristine’ as there have been no known recent mammal extinctions, and cane toads have not yet extensively invaded the region. This study was undertaken on two pastoral stations, Doongan and Theda Stations, which cover a combined area of over 6,650 km² . These stations have never previously been surveyed for the occurrence of small mammals. The investigation describes the presence, abundance and environmental relationships of the small mammal species on these stations. The records obtained in this study fill a significant gap in knowledge of the distribution and relative abundance of the small mammal species in the Northern Kimberley region. The results are compared to the small mammal fauna on three adjacent national parks, as well as to those of the broader region of northern Australia. Extensive trapping surveys of small mammals were undertaken on the two properties. However, only 15 of the 27 small mammal species known to occur in the Northern Kimberley were detected. Four species were commonly found (Pseudomys nanus, Rattus tunneyi, Zyzomys argurus and Sminthopsis virginiae). Six other species were detected, but less frequently (Leggadina lakedownensis, Pseudomys delicatulus, Pseudantechinus ningbing, Dasyurus hallucatus, Isoodon macrourus and Petropseudes dahli). The other five species were only detected occasionally (Melomys burtoni, Pseudomys johnsoni, Hydromys chrysogaster, Planigale maculata and Petaurus breviceps). The trapping success rate was found to be generally low, suggesting that populations were at low density. This indicates that the abundance and distribution of the small mammal fauna may be reduced from what would have occurred in the recent past. Environmental assessments identified 14 broad habitat types that were surveyed for small mammals across the two stations. The abundance and occurrence of small mammals in these habitats was determined. Temporal changes in trap success were evident across the nine year study period. The influence of broad-scale environmental variables on the composition of the small mammal community was examined using a relatively new modelling tool, the mvabund package. The environmental variables partially explained the variation seen across the annual survey efforts. The influence of fire and rainfall variation may have created changes in landscape productivity which, in turn, influenced the small mammal community’s composition. Land systems, which describe patterns of vegetation, topography and soils, were also associated with community composition. These systems may indicate the likelihood of species being present within the small mammal community, whilst environmental variables, such as fire and rainfall, influence the species’ ability to persist, or vary, in relative abundance.