The distribution, habitat preference and population dynamics of the pale field-rat (

Sally O'Neill,Jeff Short,Mike Calver

doi:10.1071/wr20005

Abstract

Abstract Context The pale field-rat (Rattus tunneyi) is a small native rat that formerly had a wide distribution throughout Australia. It has suffered substantial range contraction since European settlement and is now largely absent from arid and semiarid Australia. In this biome, it was known to persist only at two Western Australian locations: Edel Land, on the south-western shore of Shark Bay, and islands off the Pilbara coast. Aims We aimed to establish the extent of the species range at Edel Land, its habitat preference, the temporal stability of its populations with respect to rainfall, and threats to its persistence. Methods We trapped at 54 sites to establish distribution and habitat preference, and re-trapped four of these sites at which R. tunneyi was present in each season for 2.5 years to establish trends in abundance. Key results Trapping resulted in the capture of 45 R. tunneyi individuals across 17 of 54 sites (4104 trap-nights; 1.1% capture success). Rattus tunneyi typically occupied localised areas of dense shrubland, often in habitats with free water or near-surface moisture from drainage from high dunes allowing denser and taller vegetation and, at some sites, year-round growth of grasses or rushes. Regular re-trapping of four sites in each season (2002 – 2004) suggested a declining population, probably owing to a sequence of dry years. Key conclusions Rattus tunneyi at Shark Bay occurred only in localised mesic refuges, apparently dependent on seepage from high dunes generated by major inputs of rainfall from infrequent cyclones or sequences of high-rainfall years. Implications This isolated population is likely to be threatened by browsing by feral goats, opening up otherwise densely vegetated habitats of refuge areas, and their trampling of R. tunneyi burrows; by the depletion of grasses from herbivory by European rabbits; and by the long-term impact of a drying climate. It is unlikely to persist without effective on-going management, particularly of the goat population.

Highlights

The identification and understanding of refugia for biodiversity have become a key conservation goal, given projected anthropogenic climate change (Keppel et al 2012; Reside et al 2014)
An early attempt to identify refugia for biodiversity within Australia’s semiarid and arid zone was that of Morton et al (1995)
Braithwaite and Griffiths (1996) identified the paradox of R. tunneyi, namely, why a species that can be a pest in some areas can show signs of vulnerability to local extinction in others

Summary

Introduction

The identification and understanding of refugia for biodiversity have become a key conservation goal, given projected anthropogenic climate change (Keppel et al 2012; Reside et al 2014). An early attempt to identify refugia for biodiversity within Australia’s semiarid and arid zone was that of Morton et al (1995). These authors used the presence of relictual populations of native species as one of Journal compilation Ó CSIRO 2021 Open Access CC BY several factors to identify refugia. Relictual populations of the native rat Rattus tunneyi, isolated from the contemporary core range of the species in the north and northeast of Australia, were used to identify clusters of islands in the Pilbara and mainland peninsulas at Shark Bay that formed refugia of value to a range of other species (Morton et al 1995). The pale field-rat or djini (R. tunneyi) persists on the peninsulas of Shark Bay, being far removed from www.publish.csiro.au/journals/wr

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Conclusion