DOES VEGETATION REMOVAL INFLUENCE BIOAVAILABLE STRONTIUM ISOTOPE RATIOS (87SR/86SR)?

Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in biological materials can distinguish sedentary and highly mobile individuals, as well as identify mobility shifts in a population over time. It is usually assumed that ⁸⁷Sr/⁸⁶Sr in biological material, such as animal bone, is not impacted by anthropogenic activities like forest clearance. This assumption has not been adequately tested. Biologically available (bioavailable) strontium primarily reflects the underlying geology of the locality where an organism resides. However, factors such as soil cover, atmospheric deposition, and variable weathering rates may cause bioavailable Sr to isotopically differ from underlying bedrock. Vegetation removal may further impact bioavailable Sr if it decreases soil cover and increases physical or chemical weathering. Small mammals are ideal for assessing the impact of vegetation clearance on bioavailable ⁸⁷Sr/⁸⁶Sr because they have small home ranges and their bones integrate Sr from multiple vegetation sources resulting in less “noisy” data than that typically obtained from plants or soils. We measured ⁸⁷Sr/⁸⁶Sr in caudal vertebrae from 28 house mice (Mus musculus), black rats (Rattus rattus), and endemic tufted-tailed rats (Eliurus majori) from a minimally disturbed forest interior and an adjacent deforested site in eastern Madagascar. This region is characterized by ca. 1800 mm annual precipitation and underlain by Paleoproterozoic orthogneiss. Our results provide a first step towards validating common assumptions and determining the degree to which anthropogenic land use impacts bioavailable Sr. These findings have important implications for archeologists and paleoecologists who rely on data obtained from modern organisms to establish local or regional Sr isotopic variability.