Density of the burrowing scorpion Urodacus armatus (Scorpiones; Scorpionidae) in relation to vegetation types: implications for population decline following agricultural clearing

Abstract

The density of the burrowing scorpion Urodacus armatus in relation to vegetation type was assessed by counting the number of burrows, both the annual cohort of dispersing second instar and all older scorpions. The counts were made in 18 two metre wide transects across a 730 ha portion of Durokoppin Nature Reserve in the central wheatbelt of Western Australia. Densities were highest in woodlands (593/ha to 1950/ha), whereas in shrub and mallee associations densities were considerable lower (47/ha to 382/ha). Productivity, as measured by the ratio of second to older instar scorpions, ranged from 0.42 in low, open heath to 2.68 in Wandoo/Salmon Gum Eucalyptus capillosa/E. salmonophloia woodland. However, the correlation between productivity and the density of older scorpions in the vegetation associations was not significant. Total population in the study area was 254 954, of which 165 934 were second instar scorpions. Biomass estimates for second instar and older scorpions were 12 kg and 156 kg respectively. Observations throughout the wheatbelt indicated that the relationship between density and vegetation was comparable to that found in the study area. Using the data on the areas of the vegetation associations in the Avon Botanical District, before and after agricultural clearing (Beard and Sprenger 1984), and the densities in the present study, the abundance and biomass, pre- and post-clearing were calculated. The standing population (excluding the annual cohort) would have been of the order of 1.2 billion, with an annual influx of 2.6 billion. The biomasses would have been 690 tonnes and 210 tonnes respectively. Clearing reduced the area of habitat by 86% and the standing population by 92% and in woodland by 97%. The implications of these results for other species are discussed.