I<<'(ord, of th( W<'.,lall /\/1,111//11111 Ivl 11,<'11 III 5uPl11el11('nt No. 67: 109-137 (2004). Biogeographic patterns in small ground-dwelling vertebrates of the Western Australian wheatbelt J J J 2 Allan H. Burbidge , J.K. Rolfe , N.t. McKenzie and J.D. Roberts I Department of Conservation and I.and Management, Science Division PO Box) I Wanneroo, Western Australia 6946, Australia School of Animal Biology M092, Universitv of Western Australia, 35 Stirling Highway, Crawley, Wl'stern Australia 6009, Australia Abstract - Cround-dwelling frogs, reptiles and small mammals were sampled at 252 quadrats chosen to represent the geographical extent and diversity of uncleared terrestrial environments across the WestE'rn Australian wheatbelt. These sitE's were not overtlv affected by secondarv salinisation, but did include sites that were 'natu~ally' saline. We recorde~i a total of 144 species from 74 genera and 15 families. There was an average of 10.4 species per quadrat with a range from one to 19. Vertebrate species richness was highest on dissection valley floors and sandy depositional surfaces of the 'old plateau' but lowest on saltflats. Total species richness was positively correlated with high levels of sand, with low levels of soil nutrients and with good soil drainage. When frogs, reptiles and mammals were considered separately, temperature and rainfall attributes were also shown to exhibit correlations with species richness. Patterns in species composition could be explained in terms of climatic and substrate variables, including salinity. Two distinct faunas were identified - one concentrated in the semi-arid northern and inland parts of the study area, and one concentrated in the more mesic south and south-east. Further patterning could be discerned within this dichotomy, including the existence of a small group of species that arc associated with saline areas. Correlations between climatic and substrate variables could be discerned even at very low levels in the classification analysis, suggesting strong deterministic patterns in vertebrate species composition across the study area. Integrated management programs over entire catchments will be necessary in order to maintain conservation values, but there is doubt that the impacts ~)f salinisation and fragmentation can be mitigated quickly enough to allow the small, ground-dwelling vertebrate fauna to withstand the effects of these processes in the Western Australian wheatbelt. INTRODUCTION rainfall and dry fallout, and consisting mainly of Much of the native vegetation in south-western sodium chloride (Hingston and Gailitis, 1976). As a Australia has been removed in the pursuit of result of this, together with the subdued agricultural enterprises, just as in many other parts topography and hot climate, there are parts of the of temperate Australia. In parts of the Western landscape that are 'naturally' saline (Salama, 1994). Australian wheatbelt more than 95% of native In a terrestrial context, salinisation is a pedogenic vegetation has been replaced by annual cereals or process that concentrates salts at or near the soil herbaceous pasture plants. Removal of native surface when evapo-transpiration greatly exceeds vegetation in this area began before 1900 (Sau nders water inputs from precipitation. This can occur as a 1'/ 17/., 191'\5) and has contimlL'd to the present time. result of natural physical or chemical processes or Unfortunately, this has occurred in an area that is as a result of human activities, such as clearance of susceptible to salinisation. Not surprisingly, there native vegetation, in whid1 case it is termed has also been preferential clearing of the soils more salinisation (Chasserni cl 17/., 1995). In suited for agriculture, which are primarilv on the sou th western Australia, as in some other vallev floors and lower Such areas arc less agricultural areas in Australia and elsewhere in the well repn'sl'nted in the reserve system than, for world, replacement of native woody perennial example, areas around rock outcrops or plants with short lived herbaceous plants has breakawavs. n'sulled in major alterations to the hydrological In south-wesll'rn Australia the regolith, because cvcle, with rising water tables bringing d significant of its antiquity, contains a store of sdlt derived trum salt load near the land surface. This secondarv 110 A. H. Burbidge,]. K. Rolfe, N. L. McKenzie,]. D. Roberts salinisation has obvious deleterious consequences, structure and quality. However, even though not only for agricultural production, water quality awareness of the 'salinity crisis' is now widespread and infrastructure maintenance, but also for (Beresford et al., 2001; Sexton, 2003) little is known conservation of native plant and animal about the effects of salinisation on the native communities in the remaining remnants of the terrestrial biota, particularly on native animals original vegetation (George et al., 1995; ANZECC, (Cramer and Hobbs, 2002; Briggs and Taws, 2003). 2001; Cramer and Hobbs, 2002). In such an environment, an important first step in The link between removal of woody plants and conservation management is to document the increasing salinity levels in groundwater has been geographic distribution of plants and animals in the recognised in south-western Australia since the region and elucidate diversity patterns (e.g. Cody, early 1900s (Mann, 1907; Wood, 1924) and is now 1986). The present study was commenced as part of relatively well understood (e.g. Clarke et al., 2002). a broader study to identify biogeographic patterns Clearing of native vegetation has continued, amongst a range of plant and animal groups in the however, and nearly two million hectares (about south-western Australian wheatbelt, and to identify 10% of the wheatbelt) are now affected by regions of high conservation value. Elsewhere salinisation, with a high likelihood that the extent (McKenzie et al., 2003) we investigated the effects of could double within the next 20 years (Ferdowsian salinisation on small ground-dwelling animals in et al., 1996). The process of secondary salinisation is the Western Australian wheatbelt. In the present likely to pose a significant threat to many native paper, we explore geographic patterns in the plants and animals, through its impact on habitat communities of small ground-dwelling vertebrates 11 116 118 KAL8ARRI 120 2!1 18RA Regions o Gel'3ldton Sandplains 2 Be 3 o Pwon \fl.Iheatbelt 1 Be 2 o JarT3h Forest 1 Be 2 o Mallee 1 &2 o Espel'3nce Plains 1 Be 2 o 100 Kilometres 118 120 Figure 1 Wheatbelt study area, showing the 304 qlladrats, and relevant biogeographical region boundaries (Thackway and Cresswell1995). The different symbols indicate the 12 or 13 qlladrats in each of the 24 survey areas. Small ground-dwelling vertebrates 111 (frogs, reptiles and small marnrn,lls) at sites not sites not overtly affected by secondary salinisation. overtly affected by secondarv salinisation. Landform units were numbered from 1 to 12 Specifically, we examine patterns of species according to their position in the landscape profile richness, explore compositional variation among (Figure 2). In cases where a unit was particularly sample sites (quadrats), provide an overview of the extensive within a survey area, two quadrats were composition and distribution of specIes sampled. As well, most quadrats were pseudo­ assemblages and document relationships between replicated in the other survey areas to allow for the assemblage composition and characteristics of the internal heterogeneity of the stratification units physical environment. (hypothesised scalars) and to minimise any analytical circularity introduced by stratification (Taylor and Friend, 1984; McKenzie et aI., 1989). STUDY AREA AND METHODS Further details concerning quadrat selection are The study area extended from near Northampton provided in McKenzie et al. (2003). Locations of (latitude 28° S) to near the south coast, and from quadrats are given in Appendix 1. near the west coast east to just beyond Esperance Reptiles, frogs and mammals were pit-trapped at (longitude 123 0 E) (Figure 1). The area is each quadrat for a minimum of seven nights in both characterised by a Mediterranean climate with hot spring and autumn. The minimum of seven nights dry summers and most rainfall in winter. Annual was chosen to encompass a full weather cycle, with rainfall ranges from 300 mm in the north-east to 800 sampling in two seasons to optimise return for mm in the south-west, annual average maximum trapping effort (Moseby and Read, 2001; Read and temperature is between 24 and 37 QC and annual Moseby, 2001). Quadrats in the first third of survey average minimum temperature between 4 and 9 QC areas (central wheatbelt) were sampled from (Bureau of Meteorology, 2001). October 1997 to September 1998, while the northern The landscape is an ancient one, dating from the quadrats were sampled from September 1998 to Palaeozoic (McArthur, 1993). It is mantled with October 1999, and the southern ones, plus the sand over lateritic gravel, with dissection and Dandaragan Plateau, were sampled from October differential erosion of the old lateritic plateau 1999 to October 2000. surface resulting in a catenary of landforms and For the first 101 quadrats surveyed, the minimum soils of colluvial, alluvial, lacustrine and aeolian effort was 168 pit trap nights, using two lines of six origin and including sands, sandy loams and loams pits, 10 m apart, at each quadrat. For the remaining (sometimes over clay) low in the landscape.