Abstract:
Carbon and oxygen stable isotope analysis of mammalian carbonate bioapatite is, nowadays, a well-established and widely used approach for past ecological investigations and paleoenvironmental reconstructions. Carbon is incorporated into mammalian tissues through their dietary intake. In this regard, the ratios of stable carbon isotopes in the tissues of primary consumers—hereafter expressed using the delta (δ) notation, wherein δ13C=[(13C/12C)sample/(13C/12C)standard – 1] × 1000— reflect the isotopic composition of the ingested plant matter (DeNiro and Epstein, 1978), enriched by ~14.1 ± 0.5‰ in tooth enamel carbonate of large herbivores (Cerling and Harris, 1999; Passey et al., 2005), due to physiological and metabolic processes. In terrestrial ecosystems, variation in the isotopic signature of plant carbon permits a distinction between the two main photosynthetic pathways, i.e., C4 and C3 (Ehleringer and Monson, 1993), with the former group consisting of warm growth season grasses and forbs, which demonstrate higher average δ13C value (~13‰), and the latter incorporating trees, shrubs, and cool growth season grasses and sedges with a modern average δ13C value of ~27‰ (Bender, 1971; Kohn, 2010). Within plant communities utilizing the C3 photosynthetic pathway, additional environmentally controlled fractionation occurs, which is governed by multiple factors, such as degree of canopy closure, water availability, temperature, irradiance, or atmospheric CO2 diffusion (van der Merwe and Medina, 1991; Heaton, 1999; Hofman-Kamińska et al., 2018). The interplay of these factors enables further habitat distinctions within the wide range of δ13C values documented in C3-dominated ecosystems, since carbon isotopic ratios of herbivores feeding under closed canopy conditions, i.e., dense forests, tend to be lower than for herbivores foraging in open woodlands, open parklands and grasslands, or at the top of the canopy (Drucker et al., 2008; Bocherens and Drucker, 2013).
Stable isotopes