Oxygen and carbon isotope variations in a modern rodent community - implications for palaeoenvironmental reconstructions.

Background: The oxygen (δ(18)O) and carbon (δ(13)C) isotope compositions of bioapatite from skeletal remains of fossil mammals are well-established proxies for the reconstruction of palaeoenvironmental and palaeoclimatic conditions. Stable isotope studies of modern analogues are an important prerequisite for such reconstructions from fossil mammal remains. While numerous studies have investigated modern large- and medium-sized mammals, comparable studies are rare for small mammals. Due to their high abundance in terrestrial ecosystems, short life spans and small habitat size, small mammals are good recorders of local environments.

Methodology/findings: The δ(18)O and δ(13)C values of teeth and bones of seven sympatric modern rodent species collected from owl pellets at a single locality were measured, and the inter-specific, intra-specific and intra-individual variations were evaluated. Minimum sample sizes to obtain reproducible population δ(18)O means within one standard deviation were determined. These parameters are comparable to existing data from large mammals. Additionally, the fractionation between coexisting carbonate (δ(18)O(CO3)) and phosphate (δ(18)O(PO4)) in rodent bioapatite was determined, and δ(18)O values were compared to existing calibration equations between the δ(18)O of rodent bioapatite and local surface water (δ(18)O(LW)). Specific calibration equations between δ(18)O(PO4) and δ(18)O(LW) may be applicable on a taxonomic level higher than the species. However, a significant bias can occur when bone-based equations are applied to tooth-data and vice versa, which is due to differences in skeletal tissue formation times. δ(13)C values reflect the rodents' diet and agree well with field observations of their nutritional behaviour.

Conclusions/significance: Rodents have a high potential for the reconstruction of palaeoenvironmental conditions by means of bioapatite δ(18)O and δ(13)C analysis. No significant disadvantages compared to larger mammals were observed. However, for refined palaeoenvironmental reconstructions a better understanding of stable isotope signatures in modern analogous communities and potential biases due to seasonality effects, population dynamics and tissue formation rates is necessary.