Guanaco (Lama guanicoe) isotopic ecology in southern South America: spatial and temporal tendencies, and archaeological implications

We synthesize and discuss available isotopic data on Holocene guanaco samples from southern South America, extending from Tierra del Fuego Island to northern Patagonia and the Pampean region. We evaluate temporal and spatial tendencies on the basis of 91 samples (mainly based on δ¹³C_collagen values), presenting implications for paleodietary research in archaeology. We conclude that there are no strong correlations with latitude in the macro-spatial scale, while there is a set of interesting patterns at smaller regional scales. These patterns lead us to evaluate the role of ecologic and topographic variables (e.g. canopy effect, variations in altitude, ecotones) in structuring isotopic variability. Finally, on the basis of the present analysis we suggest a number of hypotheses and perspectives for the use of stable isotopes as geographic tracers of guanaco distribution in the past, and specific implications for the paleodietary study of human samples.     

Intrataxonomic variability in metapodial and femur bone density related to age in guanaco (Lama guanicoe). Zooarchaeological and taphonomical implications

The aim of this paper is to present new information about bone mineral density (BMD) variability in guanaco (Lama guanicoe), a South American wild camelid; while taking into account its ontogenic development. The importance of considering intrataxonomic variability in bone density related to age for constructing zooarchaeological indices and applying them to archaeological assemblages is also discussed. The results presented here were developed from a large sample of 46 metacarpals and 45 femurs of modern guanacos, ranging in age from ca. 6 months of gestation to 12 years. Bone structural densities were measured using a biphotonic X-ray densitometer, DEXA method, Norland EXCELL and the bone mineral content (BMC) of each scanned portion or complete element was divided by its volume, which was obtained independently by water displacement. Our results indicate that the bone density of each anatomical unit is highly variable, even among individuals of the same species. According to metacarpals data, age is an important factor affecting BMD. Moreover, our study shows that the density ranges of different skeletal elements can overlap, suggesting that it is not possible to predict that a certain element is always denser than another one. Finally, we present new evidence about the potential age-related taphonomic bias in faunal assemblages, indicating that meanwhile some skeletal elements show clear differences in their density between their fused and unfused state (metacarpal) other do not (femur).     

Patterns of Resource Use and Isotopic Niche Overlap Among Guanaco (Lama guanicoe), Pampas Deer (Ozotoceros bezoarticus) and Marsh Deer (Blastocerus dichotomus) in the Pampas. Ecological,Paleoenvironmental and Archaeological Implications

ABSTRACT

In this paper, we analyze the isotopic niche and resource use of the guanaco (Lama guanicoe), pampas deer (Ozotoceros bezoarticus) and marsh deer (Blastocerus dichotomus) on the temperate plain of the northern Pampa region in the southeast of South America. The measured stable isotope compositions in bone tissue are δ¹³C, δ¹⁵N and δ¹⁸O. All the analyzed samples were recovered from different archaeological sites from the late Holocene. According to the results, the guanaco was strictly confined to the Pampa plain environment, developing a broad niche based on C₃ plants and a variable contribution of C₄ grasses within a grazing trend. The pampas deer preferentially used the Pampa plain, but also the prairies on the borders of the wetland, showing eurioic characteristics and a narrower niche based on C₃ plants. In turn, the marsh deer was strictly confined to wetland environments, developing a C₃ diet–base, within a narrow isotopic niche and stenoic characteristics. The three mammals showed a wide range of intraspecific variability, which was a key factor in their adaptability to spatial and temporal changes in the vegetation coverage. In fact, the temporal trends of their isotopic values were concurrent with the major climatic variations of the Holocene. Differences in the correlations between the values of both carbon sources in both deer species compared with the guanaco suggest a distinct chemical composition of their diet and/or differences in the allocation of nutrients. The isotopic values of nitrogen and spacing of the carbon sources in guanaco (pseudoruminant) and both deer species (ruminants) show no significant differences between them, thus establishing the values for local large herbivores. Significant correlations between δ¹³C and δ¹⁵N were found in the guanaco and marsh deer. The regional and extra–regional variability in the guanaco's δ¹³C_collagen and δ¹⁵N probably reflect the clinal variations in the vegetation coverage and the amount of rainfall. The collagen isotope values in the guanaco throughout the entire Holocene show that the humid Pampa would have shifted between being a more recurrent mesic and temperate plain with minor phases of dry–mesic conditions like during the Little Ice Age, and a humid and warm one at the peaks of the Holocene Thermal Maximum and the Medieval Climatic Anomaly. The guanaco and the pampas deer adapted to all the climatic changes that happened on the humid Pampa until the biological invasions of large European mammals changed the herbivores’ guild composition of this vast plain, pushing them into peripheral habitats due to competition. The within–species variability in isotopic signals through time and space make it necessary to carry out adequate sampling before reconstructing the diets of local past populations.