Exploring the relationship between sampling efficiency and short-range endemism for groundwater fauna in the Pilbara region, Western Australia

1. Identifying the existence of short or narrow range endemic species is an important issue when planning for conservation of groundwater fauna in the face of threats to groundwater quantity and quality. 2. Fourteen bores were sampled six times over 3 or 4 years to assess the reliability of net-hauling sampling in broad-scale survey to collect the groundwater fauna present at a site and to identify short-range endemic (SRE) species. 3. Species accumulation curves suggested that one sample from a bore collected 23% and 46% of species occurring in low and high abundance, respectively, and two samples collected 38% and 65% of such species. False-negative rates provided a slightly higher estimate of the collection probability of species with low abundances. 4. The frequent failure to collect species present at a site means that some apparent short-range endemism was probably an artefact of low sampling effort. Nevertheless, as is typical for subterranean fauna, a high proportion of the known species in the Pilbara region appeared to be SREs. About 55% had probable ranges <10 000 km², the criterion proposed by Harvey (2002) for short-range endemism. 5. Consideration of species occurrence patterns, natural barriers and the scale of most disturbances suggest that 1000 km² is a more satisfactory threshold for short-range endemism than 10 000 km² but, as the threshold is reduced, more intensive sampling is required to determine whether a species qualifies as an SRE. 6. Extrapolation of the results of regional sampling suggested the Pilbara contains about 500-550 species of groundwater fauna, with the density of species being relatively uniform across the region. Attempts to use a T-S curve approach (sensu Ugland & Gray, 2004 ) highlighted the lack of information about within-population dispersal of these species and the area of an aquifer that is effectively sampled by a bore.