Isotopic Investigations of Pastoralism in Prehistory

Alicia Ventresca Miller, Cheryl Makarewicz, Alicia R. Ventresca Miller, Cheryl A. Makarewicz

• Editorial: Routledge
• Año: 2017
• ISBN:
  9781351389914
• Edición: 1
• Categoría: Sciences sociales
• Categoría: Archéologie

Pastoralists were a vital economic and social force in ancient societies around the globe, transforming landscapes poorly suited for agriculture into spaces of vast productive potential while simultaneously connecting mobile and sedentary communities alike across considerable distances.

Drawing from the rich archaeological records of Asia, Africa, and Europe, Isotopic Investigations of Pastoralism in Prehistory brings together the latest studies employing heavy and light stable isotopic analyses of humans and animals to investigate pastoralist diets, movement, and animal management strategies. The contributions presented in this volume highlight new methodological developments while simultaneously drawing attention to the diverse environmental factors that contribute to isotopic variation in human, plant, and animal tissues. Particular attention is paid to how pastoralist decisions regarding animal pasturing and mobility can be teased out of complex isotopic datasets, and also to the challenges in extracting information on the scales of human mobility in pastoralist landscapes.

This volume will appeal to scholars in archaeology, anthropology, and ecology, as well as those with interests in animal management.

Chapter 1
Isotopic approaches to pastoralism in prehistory

Diet, mobility, and isotopic reference sets

ALICIA R. VENTRESCA MILLER AND CHERYL A. MAKAREWICZ

INTRODUCTION

Pastoralism involves the exploitation of domesticated livestock and has been a vital component of human subsistence and surplus economies for thousands of years. By supplying their human caretakers with ready and renewable sources of milk, meat, fat, fiber, skins, and dung, livestock serve as an important source of subsistence and wealth in pastoralist communities. Despite the pivotal role of livestock and animal products in defining pastoralist production, surprisingly little is known about the relationship between pastoralist dietary intake, mobility, the husbandry management strategies used by pastoralists to extract resources from their animals, and how these elements structure ancient sedentary and mobile communities engaged in livestock herding. Identifying and explaining the rich diversity in pastoralist subsistence strategies and mobility are key to understanding broader processes associated with the emergence and evolution of pastoralist social organization, ideological systems, and political formations (Makarewicz 2011; Honeychurch and Makarewicz 2016).

Stable isotope analysis (SIA) of human and animal skeletal tissues measure dietary intake and geospatially sensitive environmental inputs that capture the scalar dynamism of pastoralist movement and subsistence strategies that together inform pastoralist social networks and political organizations. So far, archaeo-logical approaches to documenting pastoralist dietary intake and livestock exploitation have relied on a sparse zooarchaeological and paleobotanical record, while reconstruction of pastoralist mobility has been based on largely indirect measures that draw from the spatial relationships of ancient campsites, monuments, settlements, and resources. While these approaches have provided important insights into pastoralist subsistence and landscape use in various environmental and social contexts, the stable isotopic record documents directly and at high resolutions the movement and dietary behaviors of pastoralists and their animals.

This volume explores the ways in which stable isotopic analyses of both human and animal skeletal remains are providing new information on pastoralist dietary intake, mobility, and animal management strategies in a variety of settings, from sedentary and semisedentary agro-pastoralist communities largely focused on plant agriculture accompanied by low-level animal husbandry to more mobile pastoralist groups heavily dependent on their livestock for subsistence. The chapters presented here tackle these issues from a variety of perspectives that consider, to varying degrees, variation in environmental isotopes, animal behavior, and pastoralist decision making and how these influence the isotopic composition of archaeological human and animal skeletal materials obtained from pastoralist contexts. In doing so, these emphasize the complexity of establishing pastoralist dietary intake, movement, and livestock management strategies using a stable isotopic approach. Rather than advocating a ‘one-size-fitsall’ approach, this volume emphasizes that undertaking stable isotopic analyses on human and animal skeletal remains recovered from pastoralist contexts requires careful consideration of the local environmental conditions that influence the distribution of isotopes on a landscape, animal physiology, and the temporal resolution of skeletal material sampled for isotopic analyses.

STABLE ISOTOPIC FOUNDATIONS OF PASTORALIST DIET AND MOBILITY

The contributions presented in this volume each explore different ways that stable isotopic analyses can be used to successfully document ancient pastoralist diet, mobility, and husbandry strategies. They all share, either explicitly or implicitly, a common concern with spatial variation in environmental isotopes and how best to establish the range of variation in the ancient landscapes under study. As part of this introduction, we draw this theme out further and critically examine how so-called baselines are constructed and inform, for better or for worse, the interpretation of stable isotope values obtained from human and animal skeletal material. We explore the promises and limitations of baselines in isotopic studies conducted in pastoralist contexts and examine alternatives, in particular isoscapes, that may be better suited for isotopic studies focused on understanding pastoralist lifeways.

The use of stable isotope analysis to trace the dietary intake and mobility of humans and livestock depends heavily on the adequate characterization of the spatial distribution of different isotopic species on the landscapes through which people and animals move, the discrimination factors for the tissue under study, and tissue turnover rates (Peterson and Fry 1987; Boutton et al. 1988; Michner and Schell 1994; West et al. 2006; Hobson et al. 2010). If one of the primary aims in the study of archaeological materials is to connect the isotopic ratio measured from ancient tissues to the ancient biochemical environment within which people and animals lived (Bentley 2006), then establishing appropriate frames of isotopic reference should be a central focus of archaeological isotope research designs.

We briefly review here environmental carbon, nitrogen, oxygen, and strontium isotope dynamics in vegetation, hydrological, and geological systems with particular attention to the dynamic geological and environmental variables that influence the distribution of these isotopes at local and regional scales. Achieving adequate isotopic reference sets and establishing the mechanisms driving isotopic variation is challenging in modern environments where environmental inputs are known, and even more so in ancient environments where climate conditions, seasonality, and landscape formations are either poorly defined or defined at regional scales that may not identify environmental variation at the local scales in which human activities take place (Contreras 2016). Although there is no one single method that best characterizes the range of natural isotopic variation in environments and food-webs accessed by ancient pastoralists, creative isotopic research that constrains for environmental inputs in order to extract a more detailed record of ancient pastoralist behaviors can provide new insights into pastoralist diet, mobility, and animal management strategies in various (pre)historic contexts in around the world.

STRONTIUM ISOTOPES, BIOAVAILABILITY, AND DYNAMIC LANDFORM PROCESSES

The movement of pastoralists and their livestock herds is impacted by a complex intersect of environmental conditions, social relationships, and political terrains (Wright and Makarewicz 2014; Honeychurch and Makarewicz 2016). Recent work has relied heavily on the use of strontium isotopes for the purposes of establishing the mobility of pastoralists and their animals largely because radiogenic strontium isotopes (⁸⁷Sr/⁸⁶Sr) are sensitive to geospatially defined geological variation in the landscape (e.g. Tafuri et al. 2006; Gerling et al. 2012; Giblin et al. 2013; Gerling 2015). Strontium isotopes do not fractionate when passed along the food chain, making strontium isotope analysis an attractive method for the purposes of establishing mobility in human and animals in ancient environments (Ericson 1985; Ericson 1989; Bentley 2006). The ⁸⁷Sr/⁸⁶Sr ratio of soil and precipitation are reflected in plants, which are consumed by, and reflected in, herbivores and humans (Beard and Johnson 2000). The three main components of strontium in plants are soil (source of nutrients for plants), precipitation, and atmospheric dust, with soil being the major contributor as it has the greatest Sr concentration (Ǻberg 1995). Strontium composition of soils can change through time due to climatic effects and anthropogenic inputs (Ǻberg 1995). Bioavailable Sr ratios are variously influenced by precipitation, sea spray, environmental pollution, and the application of fertilizer (Price et al. 2002; Bentley 2006; Evans et al. 2010; Maurer et al. 2012).

Several approaches have been employed in archaeological studies in an effort to characterize ‘local’ strontium isotope signatures. These include strontium measurements of bedrock, soils, plants, and water that are collected from present-day landscapes local to the archaeological site of interest, as well as measurement of archaeological skeletal tissues from wild or domesticated animal taxa with small home ranges (Hoppe et al. 1999; Price et al. 2002; Montgomery et al. 2007; Hodell et al. 2012; Giblin et al. 2013). Each method has strengths and weaknesses for the purposes of establishing ‘local’ strontium isotopic variation in archaeological contexts. The direct measurement of soil or bedrock was previously common practice (Sillen et al., among others), however the strontium isotopic composition of bedrock is not a consistent predictor of bioavailable strontium, and its isotopic composition can differ substantially from soils, water, and organisms (Capo et al. 1998; Bataille and Bowen 2012; Hartman and Richards 2014). Moreover, soil strontium is not wholly available to plants, which uptake only labile strontium from the soil (Capo et al. 1998). Most archaeological stable isotopic studies now measure bioavailable strontium in modern plants, water, and animals in order to establish the strontium isotopic composition in locales of archaeological interest (Schwarcz et al. 2010).

The composition of bioavailable strontium isotopes is frequently established through the isotopic analysis of local vegetation or animals with a limited range of mobility, in particular microfauna such as snails and mice (Beard and Johnson 2000; Price et al. 2002; Giblin 2009). The strontium isotopic composition of vegetation reflects the sources of cations available to plants (for discussion, see Capo et al. 1998) and plants are only able to uptake strontium that is easily exchangeable (Beard and Johnson 2000). However, caution must be exercised when using plants as a means to define local bioavailable strontium. Modern vegetation can be affected by the introduction of isotopically distinct industrial fertilizers, sometimes to great effect (e.g. Szpak et al. 2013).

Microfauna, including snails and mice, with limited mobility, also reflect environmentally bioavailable strontium (Sillen et al. 1998; Blum et al. 2000; Maurer et al. 2012). As was the case for plants, however, modern microfauna may ingest food characterized by strontium isotope composition that is very different from local environmental strontium isotopes, either directly through introduced foods or indirectly through ingestion of foods isotopically modified by modern fertilizers (Bentley 2006). However, microfauna identified within archaeological contexts along with the skeletal materials of interest, offer a good approximation of the bioavailable Sr from the local ancient environment. Archaeological microfauna may provide a good comparative reference set as they are temporally analogous to the individuals under study and are not affected by shifting Sr values over time.

Perhaps most problematic, particularly for regions of the world characterized by dynamic landscape formation processes, ⁸⁷Sr/⁸⁶Sr values obtained from modern plants and water samples may not reflect those of the ancient environment of interest (Sillen et al. 1998; Stewart et al. 1998; Bataille and Bowen 2012). However, the comparison of Sr values derived from modern small mammals with ancient micromammal strontium isotope values may be useful in determining the stability of bioavailable Sr signals in a given location over time. Analysis of archaeological wild fauna characterized by wide home ranges or herded domesticates are not necessarily appropriate for establishing a ‘local’ strontium isotope signal, but offer additional information about the variation in Sr ratios over broader landscapes.

GEOSPATIAL SENSITIVITY OF OXYGEN ISOTOPES IN HYDROLOGICAL SYSTEMS

Pastoral societies are often characterized as mobile, partially in relation to the movement of herds across the landscape. While strontium has been the most commonly used isotope to identify residential origins, oxygen isotopes derived from mineralized tooth enamel have been increasingly used to further delineate movement in pastoralists and their livestock (Balasse et al. 2012; Gerling et al. 2012). Approaches that utilize δ¹⁸O to examine movement take advantage of geospatial variation in the distribution of oxygen isotopes in meteoric waters. However, the use of oxygen isotopes to explore mobility of humans and animals from the same location is complicated, as different species vary – in patterns of landscape use, ingestion of sources of environmental water (leaf/surface), drinking rates, and respiration (Longinelli 1984; Luz et al. 1984; Luz and Kolodny 1985; Levinson et al. 1987; Daux et al. 2008). In addition, oxygen isotopes are influenced by temperature, aridity levels, rainfall amount, ...