Strontium isotope analyses of large herbivore habitat use in the Cape Fynbos region of South Africa |
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Authors: | F G T Radloff L Mucina W J Bond P J le Roux |
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Institution: | (1) Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa;(2) Present address: Department of Environment and Agriculture, School of Science, Curtin University of Technology, GPO Box U1987, Perth, WA, 6845, Australia;(3) Botany Department, University of Cape Town, 7700 Rondebosch, Cape Town, South Africa;(4) AEON EarthLAB/Department of Geological Sciences, University of Cape Town, 7700 Rondebosch, Cape Town, South Africa |
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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 87Sr/86Sr isotope ratios of rodent teeth to establish the isotopic signal characteristic of the different geological substrates in
the area. We then analysed 87Sr/86Sr 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. |
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