Strontium isotope analyses of large herbivore habitat use in the Cape Fynbos region of South Africa

Abstract

The Cape Fynbos region of South Africa, a global biodiversity hotspot, hosted a diverse large mammal fauna till shortly after permanent European settlement (1652). How these animals survived in this exceptionally nutrient-poor environment is puzzling and it is generally believed that they restricted their movements to the more fertile shale areas. We tested the hypothesis that large herbivores avoid nutrient-poor limestone and sandstone fynbos shrublands in favour of shale-derived renosterveld vegetation using strontium (Sr) isotope analysis. If this technique could reconstruct the preferred feeding habitats of the contemporary fauna, it might also be useful for reconstructing the preferred feeding grounds of an extinct fauna. Using the assumption that small rodents have spatially restricted foraging activities, we determined the (87)Sr/(86)Sr isotope ratios of rodent teeth to establish the isotopic signal characteristic of the different geological substrates in the area. We then analysed (87)Sr/(86)Sr isotope ratios in the bones of a number of different large herbivores found in De Hoop Nature Reserve using laser ablation multi-collector inductively coupled plasma mass spectrometry. These values were compared to the bioavailable (rodent) values on the respective geological substrates. The technique identified differences in feeding substrate selection between different species and groups of the same species. The results also showed that shale renosterveld shrubland is not the exclusive source of nutrition for the large herbivores. Strikingly different isotope ratios among individuals in some populations pointed to significant dispersal events from distant sources. However, we were unable to pinpoint the exact feeding areas using Sr isotope analysis probably because some animals use a combination of substrates for feeding and because the geology of the study area is complex with graded isotope signals. We suggest that this technique is a valuable additional tool for exploring large mammal foraging behaviour on habitats associated with contrasting and less complex geology.

Strontium isotope analysis of curved tooth enamel surfaces by laser-ablation multi-collector ICP-MS

“…Depending on the study, the solution 87 Sr/ 86 Sr compositions for these in-house standards are either the same teeth dissolved after laser ablation sampling (e.g. Copeland et al, 2008;Radloff et al, 2010;Copeland et al, 2011) or in some current studies the contralateral. The complete tooth is dissolved, enamel plus dentine, for conventional solution MC-ICP-MS analysis to ensure the resulting 87 Sr/ 86 Sr value is representative of all possible variability present.…”

“…86 Sr/ 88 Sr and 179 Hf/ 177 Hf) which are routinely used to monitor and correct for instrumental isotopic mass fractionation during solution or LA-MC-ICP-MS isotopic analysis (as in e.g. Radloff et al, 2010;Copeland et al, 2011). Such continuous, internal correction for instrumental isotopic mass fractionation during LA-MC-ICP-MS analysis can effectively correct for all laser or plasma-source isotope fractionation and yields accurate isotope ratio results as noted in Jackson and Günther (2003).…”

“…Richards et al, 2008;Radloff et al, 2010;Copeland et al, 2011;Balter et al, 2012;Moffat et al, 2012). This method can yield a relatively large number of strontium isotope values for tooth enamel within a relatively short timescale, with sufficient resolution for many bioecological studies.…”

Strontium isotope variation and carbonate versus silicate weathering in rivers from across Alaska: Implications for provenance studies

“…In the last two decades strontium (Sr) isotope ( 87 Sr/ 86 Sr) ratios of mineralized tissues of animals, such as tooth enamel, bone apatite, and otolith aragonite (auditory structure of teleost fish) have been used to elucidate the modern and paleoecology of organisms, both in the terrestrial (Hoppe et al, 1999;Beard and Johnson, 2000;Hodell et al, 2004;Hoppe and Koch, 2007;Britton et al, 2009;Sellick et al, 2009;Radloff et al, 2010;Britton et al, 2011) and aquatic realms (Koch et al, 1992;Kennedy et al, 1997;Kennedy et al, 2000;Kennedy et al, 2002;Outridge et al, 2002;Barnett-Johnson et al, 2008;Walther et al, 2008;Miller and Kent, 2009;Barnett-Johnson et al, 2010;Miller, 2011;Muhlfeld et al, 2012). 87 Sr/ 86 Sr ratios are particularly well suited for provenance studies because: i) 87 Sr/ 86 Sr ratios of biogenic tissues directly reflect source materials Bentley, 2006;Barnett-Johnson et al, 2008;Muhlfeld et al, 2012); ii) Sr is relatively abundant in Ca-bearing minerals and tissues (e.g.…”

Bioavailable 87Sr/86Sr in different environmental samples — Effects of anthropogenic contamination and implications for isoscapes in past migration studies

“…Over the past decade, strontium (Sr) isotope analysis has become an increasingly powerful tool in present-day and past animal ecology, for determining habitat use and mobility/migration (Blum et al, 2001;Britton et al, 2011;Feranec et al, 2007;Hoppe et al, 1999;Hoppe and Koch, 2007;Radloff et al, 2010;Tütken et al, 2011), in tracing food provenance (Almeida and Vasconcelos, 2001;Barbaste et al, 2002;Fortunato et al, 2004;Montgomery et al, 2006;Swoboda et al, 2008;Techer et al, 2011;Voerkelius et al, 2010), in hydrological and forest ecosystem investigations (Böhlke and Horan, 2000;Dijkstra et al, 2003;Drouet et al, 2005bDrouet et al, , 2007Poszwa et al, 2004;Shand et al, 2009), as well as in forensic sciences (Beard and Johnson, 2000;Juarez, 2008).…”