QA_Vol 24_No 1_July 2007 - Australasian Quaternary Association

isotope tissue values. Differences in C 3 grass δ 13 C tissuevalues will be passed on to herbivores. Thus, in additionto differences in the distribution and abundance of C 3versus C 4 grasses across various habitats, stable carbonisotope variability within C 3 grasses introduces anadditional mechanism that will affect herbivore bonecollagen δ 13 C composition.Materials and MethodsSamples of C 3 pasture grasses (Barley grass, Hordeumleporinum) were collected at five field sites in southeasternSouth Australia with mean annual rainfallvalues ranging from 1045 mm to 238 mm. The collectionsites included Bridgewater, Mount Barker, Coonalpyn,Pinnaroo, and Morgan (Figure 1). Bridgewaterand Mount Barker are located within the Adelaide Hillsregion to the southeast of the city of Adelaide. Fivesamples of grass were collected at each site from a 25m 2 area of flat pasture ground in areas that were notirrigated. Grass blades were cut near the top of the plantto avoid contamination from the underlying soil.Samples were submitted to the CSIRO Land and Waterlaboratory, Adelaide for stable carbon isotope analysis.Samples were oven dried at 50°C, ground, and analysedby mass spectrometer using an automated EuropaScientific ANCA-SL system with on-line separation.Analytical precision was better than ± 0.1‰.ResultsStable carbon isotope values of C 3 grasses become lessnegative with decreasing mean annual rainfall. Meanδ 13 C values vary from -31.5‰ at Bridgewater (1045 mmrainfall) to -27.7‰ at Morgan (238 mm rainfall), a 3.8‰difference correlated with a change of mean annualrainfall of 807 mm (Table 1). The greatest magnitude ofgrass tissue δ 13 C change (2.5‰) occurs between thesemi-arid (Pinnaroo, 345 mm rainfall) and arid(Morgan, 238 mm rainfall) zones, whereas there is nosignificant difference (0.3‰) between mean values atthe Pinnaroo and Coonalpyn (453 mm rainfall)collection sites.Differences in δ 13 C values for grasses between temperatecoastal and arid interior habitats are reflected inthe bone collagen δ 13 C values of herbivore consumers(Table 2; Figure 1). For example, the difference in meanδ 13 C values for grasses at Mount Barker (767 mm rainfall)versus Morgan (238 mm rainfall) is 3.2‰, while thedifference between grey kangaroo (Macropus fuliginosus)bone collagen values at Mount Gambier (775mm rainfall) versus Morgan is 3.4‰ (Pate and Noble,2000; Pate and Schoeninger, in review). Mean δ 13 Cvalues in C 3 grasses from a majority of the temperateand semi-arid regions in South Australia that areoccupied by kangaroos differ by only 0.3 to 1.0‰.Table 1.Collection Site Location Mean Annual Mean Grass Range nRainfall (mm) 13 C (‰) ± SDBridgewater 35 00’ S, 138 45’ E 1045 -31.5 ± 1.1 -33.4, -30.5 5Mount Barker 35 04’ S, 138 52’ E 767 -30.9 ± 1.0 -32.2, -29.6 5Coonalpyn 35 42’ S, 139 50’ E 453 -29.9 ± 1.2 -31.5, -28.7 5Pinnaroo 35 16’ S, 140 54’ E 345 -30.2 ± 0.7 -31.3, -29.4 5Morgan 34 01’ S, 139 39’ E 238 -27.7 ± 0.7 -28.4, -26.6 5Stable carbon isotope variability inC3 grasses (Barley grass, Hordeumleporinum) at five South Australiancollection sites along a rainfallgradient from temperate coastal toarid interior.Table 2.Collection Site Location Mean Annual Percentage a Kangaroo b nRainfall (mm) C 4 Grasses 13 C (‰)Mount Gambier 37 56’ S, 140 47’ E 775 23 -24.8 6Karte 35 04’ S, 140 42’ E 350 47 -21.6 7Morgan 34 01’ S, 139 39’ E 238 47 -21.4 6Plumbago 32 04’ S, 139 53’ E 200 69 -17.6 13Innamincka 27 56’ S, 140 47’ E 176 78 -15.4 12Mean bone collagen stable carbonisotope results for South Australiankangaroos collected along a southnorthtransect from temperate coastto arid interior (after Pate and Noble,2000; Pate, unpublished data forMorgan site).a: After Hattersley (1983)b: Grey kangaroos (Macropus fuliginosus) for Mount Gambier, Karte, and Morgan;Red kangaroos (Macropus rufus) for Innamincka; Red and grey kangaroos for Plumbago31 | Quaternary AUSTRALASIA 24 (2)