Master of Science (Research)
School of Biological Sciences - Faculty of Science
Norton, Melinda A, Habitat associations of the long-nosed potoroo (potoroos tridactylus) at multiple spatial scales, MSc thesis, School of Biological Sciences, University of Wollongong, 2009. http://ro.uow.edu.au/theses/832
The long-nosed potoroo (Potorous tridactylus) is a threatened, ground-dwelling marsupial known to have been highly disadvantaged by changes brought about since European settlement in Australia. Key threats to the species are believed to be fox predation and habitat loss and/or fragmentation. In order to conserve the species, the important habitat elements for the species at both the coarse and fine scale need to be identified and managed appropriately. The aims of this study were to examine the coarse- and fine-scale habitat preferences of the long-nosed potoroo, using a variety of techniques, in two National Park reserves (Barren Grounds Nature Reserve and Budderoo National Park) in the Southern Highlands of New South Wales in order to inform management. The ecology of the long-nosed potoroo in this region is poorly understood, making this study both timely and critical. Assessments of the morphometrics of the local long-nosed potoroo populations and their relative abundance, in addition to fox predation pressure at these localities, were also undertaken to assist in the conservation of the local potoroo population.
Live-trapping was conducted in autumn and spring, from 2004 to 2008, at 103 trap sites across the two study areas and morphometric data were collected. The local long-nosed potoroos were found to be larger in size than Victorian animals but smaller than north-eastern NSW animals supporting the concept of a cline in body size for the species with weight increasing with latitude on the mainland. Sexual dimorphism was also observed with adult males having larger body weights, head lengths and pes lengths. Between one to two thirds of all males and females at either study area were only captured in a single trapping session, indicative of high levels of transience and/or low levels of survivorship.
Of the two study areas, Barren Grounds Nature Reserve supported a larger number of individuals and appeared to have a greater degree of home range overlap between individuals, which was considered indicative of a higher quality habitat at this study area. Overall, the two study area populations appear to have increased over the course of the study. The sand plot technique, used in both study areas each Autumn and Spring from 2005 to 2008 as a second technique to monitor potoroo relative abundance, was considered less effective than trapping. This was due to its inability to decipher between individuals with overlapping home ranges in higher density populations and the species’ reduced utilisation of tracks compared to many other species.
A number of habitat attributes were examined at each trap site to allow comparison with trap success ratings as an indication of macrohabitat preferences. In Spring 2007 and Autumn 2008, microhabitat use was also examined at both study areas, using the spool-and-line technique and an assessment of forage diggings. The results indicated that while potoroos were trapped at sites with a wide range of macrohabitat attributes, the species displayed a number of macrohabitat preferences, particularly for greater levels of canopy and shrub cover, for ferns as a dominant ground cover type and for lower levels of floristic diversity in ground cover. Differences in the macrohabitats present at each study area, as well as those preferred at either study area, were also observed. Microhabitat attributes were assessed along the spool paths as well as in the available habitat to allow comparison of observed and expected usage. The spooling results revealed that while most individual potoroos had significant preferences for some microhabitat attributes, no clear trends were evident across all individuals spooled. Comparison of the presence/absence of forage diggings and associated microhabitat attributes at systematic sample points within the available habitat was also undertaken. Potoroos also displayed preferences for foraging in locations with higher shrub cover densities and more open ground cover. Between the two scales of investigation, patterns of habitat preferences differed. The species’ habitat use appears to be influenced by both macro- and micro-scale preferences, highlighting the importance of examining habitat associations at multiple scales.
The relative abundance of foxes fluctuated over the study as indicated by sand plots monitored in both Autumn and Spring from 2005 to 2008 in both study areas. Yet despite the often high fox predation risks, individual potoroos were not all preferentially utilising higher levels of ground cover or habitat complexity. Despite dense vegetative cover being a common attribute in potoroo habitat, my results support the theory that the species requires habitat patchiness, with structural and floristic preferences varying during different activities. This includes the use of relatively open, floristically-diverse patches for foraging activity, providing some level of cover from aerial but not ground predation during foraging. Analysis of fox scats at the same study sites indicated a high prevalence of potoroo remains. Consequently, it was not considered likely that the species is afforded adequate protection against fox predation by its use of habitat.
Future management should aim to perpetuate the diversity of vegetation attributes at each of the study areas while avoiding practices that simplify such habitat. The effective control of foxes in and around potoroo habitat was also considered likely to assist in the conservation of the species.
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