Human ecological niches and ranges during the LGM in Europe derived from an application of eco-cultural niche modeling
Introduction
The idea of modeling past human–environment interactions is by no means new. Researchers have used archaeological and environmental data sets, and diverse methods, to interpret prehistoric hunter-gatherer behavior in ecological contexts. Well-known European examples concern prehistoric population distributions during Oxygen Isotope Stages 2 and 3 (Gamble et al., 2004, Van Andel and Davies, 2003), as well as the resettlement of regions following severe climatic episodes (Gamble et al., 2005, Straus et al., 2000). These studies were based on spatial distributions of radiometrically dated sites and generalized climatic reconstructions. Others have used a similar approach to estimate population size and kinetics (Bocquet-Appel and Demars, 2000, Bocquet-Appel et al., 2005). More detailed attempts to examine population distributions and human tolerances with respect to environmental variability also exist (Binford, 1999, Binford, 2001, Davies et al., 2003, d'Errico and Sánchez-Goñi, 2003, d'Errico et al., 2006, Sepulchre et al., 2007). However, no agreement yet exists on how best to evaluate influences of environmental factors on prehistoric human populations and their responses to climatic variability.
One common limitation is the use of coarse-scale climatic data (i.e., simulations with resolutions of 3–5° in latitude and longitude) and imprecise chronological data (i.e., reliance on old conventional ages with large sigmas) that make evaluation of human responses to rapid-scale climatic variability, with adequate resolution, difficult. Another shortfall of previous studies is that they have incorporated environmental data into analyses only passively, such that these data are used as backdrops against which the archaeological record is interpreted. While these studies have obvious value, they are limited in their ability to evaluate prehistoric hunter-gatherer responses to the abrupt climatic and environmental changes of the last glacial period. The need for robust methods with which to evaluate more precisely how past human and animal populations responded to these changes is critical.
An important recent advance in the study of biological diversity has been the development of biocomputational architectures for predictive modeling of complex biodiversity phenomena (Guisan and Zimmermann, 2000, Soberón and Peterson, 2005). Such tools can be used to predict species' range (i.e., ecological niche) expansion or contraction in response to real or simulated climatic changes (Peterson et al., 2002). The ecological niche of a species can be defined as the range of environmental conditions within which it can persist without immigrational subsidy (Grinnell, 1924, Hutchinson, 1957). Such methods have considerable potential for reconstructing niches of past human populations and for illuminating the complex mechanisms that regulated the interactions between past hunter-gatherer populations and their environments, which in turn helped shape cultural, genetic, and linguistic geographies. These methods, and related concepts, recently have been termed eco-cultural niche modeling (ECNM) (Banks et al., 2006) when applied to prehistoric human populations. Our application of ECNM interactively integrates climatic, geographic, and archaeological data via a machine-learning genetic algorithm, described below. Comparable work is being pursued by others to analyze North American Paleoindian (Anderson and Gillam in Banks et al., 2006) and Far Eastern Paleolithic (Gillam and Tabarev, 2006) data and have shown promising results. We argue that ECNM is a powerful approach and, when paired with high-resolution climatic simulations, allows one to overcome many limitations of previous studies and evaluate prehistoric human–environment interactions at regional scales.
Here, we apply ECNM to human populations at the Last Glacial Maximum (LGM) in Europe, a well-studied and dated climatic phase known to have had profound impacts on human populations, with three primary objectives: (1) to determine the limits of the potential human range during the LGM, (2) to define the eco-cultural niches of the two main archeological cultures present in Europe at that time (the Solutrean and Epigravettian technocomplexes), and (3) to identify environmental and cultural factors that shaped their geographic ranges.
The last glacial period was marked by dramatic and rapid climatic variability (Dansgaard et al., 1993, Johnsen et al., 1992), with the LGM representing a unique suite of climatic conditions (Ditlevsen et al., 1996, Peyron et al., 1998). This period, centered on 21 kyr cal BP, is characterized by the maximum volume of the ice sheet over Scandinavia and northern Europe, along with cold and generally arid conditions in northern and Western Europe. The LGM archaeological record is characterized by a relatively small number of sites and large gaps in the archaeological record for many regions (cf. Soffer and Gamble, 1990, Straus, 2005, Street and Terberger, 1999). Such a pattern has been interpreted to be the result of the human abandonment of northern Europe and a contraction of the human range to southern regions that served as refugia. Such contraction and consequent demographic reduction is known to have produced a bottleneck in human genetic diversity (Barbujani et al., 1998: p. 490; Torroni et al., 2001, Torroni et al., 1998).
In Western Europe, between ca. 22 kyr and 20 kyr cal BP, human groups responded to LGM environmental conditions by developing a suite of new technologies characterized by a variety of diagnostic projectile points and knives produced by bifacial retouch (Fig. 1A), which define the Solutrean (Mortillet, 1873, Smith, 1966). Straus (2005) proposed that Solutrean populations employed more specialized subsistence systems, relative to earlier Upper Paleolithic technocomplexes, to exploit regions rich in game but under harsh climatic conditions.
In the regions of southeastern Europe, hunter-gatherers of the LGM produced a different lithic technology, termed the early Epigravettian (Laplace, 1964, Mussi, 2001), characterized by shouldered and backed projectile points produced by unifacial retouch (Fig. 1B). Leaf-shaped points are rare and have been recovered from only a few sites in northern Italy (Palma di Cesnola, 1990). Contrary to the Solutrean, which appears as a novel technology, the Epigravettian toolkit is interpreted as being derived from the preceding Gravettian technocomplex (Otte, 1990, Palma di Cesnola, 2001).
Section snippets
Materials and methods
For ECNM, we employed a machine-learning genetic algorithm originally developed for determining the ecological niches of plant and animal species (Stockwell, 1999, Stockwell and Peters, 1999). This software application, termed the Genetic Algorithm for Rule-Set Prediction (GARP), has been applied to topics as diverse as habitat conservation, effects of climate change on species' distributions, the geographic potential of species' invasions, and anticipation of emerging disease transmission risk
Results
The model produced using both Solutrean and Epigravettian sites identifies a clear northern boundary for potential human range during the LGM (Fig. 4), which is also reproduced in the models for each separate technocomplex (Fig. 5). This boundary follows the Loire valley in France, excludes the Massif Central, includes the Mediterranean regions of France, follows the southern limit of the Alps, and the northern limits of the Carpathian range (Fig. 4).
The territories predicted for the Solutrean
Discussion
The northern limits of the human range predicted by ECNM for the LGM (Fig. 4) are arguably accurate. These limits are consistent with the known distribution of archaeological sites for this period (Bocquet-Appel et al., 2005, Demars, 1996, Soffer and Gamble, 1990). The only radiometrically dated site for our temporal range that seemingly contradicts our results is that of Wiesbaden-Igstadt (Street and Terberger, 1999), which has yielded seven AMS ages from a single occupation level ranging from
Conclusions
ECNM is an effective approach by which to characterize and quantify eco-cultural niches associated with specific technocomplexes, and better understand how environmental factors influenced distributions of prehistoric human populations. Future research must focus on methods that can be used to evaluate more precisely the roles of competition and cultural cohesiveness in producing discords between predicted and actual ranges. The role of geography in constraining niches and creating cultural
Acknowledgements
We thank María Fernanda Sánchez Goñi, Marco Peresani, and Paolo Biagi for helpful discussions, and Françoise LaGarde for making Fig. 7. We especially thank Barbara Wohlfarth for her support as leader of RESOLuTION, a project with the European Science Foundation's EuroCores on EuroCLIMATE program, which made this research possible. We also thank the two anonymous reviewers whose comments improved the manuscript. This research was also funded by the OMLL program of the European Science
References (78)
- et al.
Evaluating predictive models of species' distributions: criteria for selecting optimal models
Ecological Modelling
(2003) - et al.
Evidence for Paleolithic and Neolithic gene flow in Europe
American Journal of Human Genetics
(1998) Long-term variations of caloric solar radiation resulting from the earth's orbital elements
Quaternary Research
(1978)- et al.
Population kinetics in the Upper Paleolithic of Western Europe
Journal of Archaeological Science
(2000) - et al.
Estimates of Upper Paleolithic meta-population size in Europe from archaeological data
Journal of Archaeological Science
(2005) - et al.
Neanderthal extinction and the millennial scale climatic variability of the OIS 3
Quaternary Science Reviews
(2003) - et al.
Predictive habitat distribution models in ecology
Ecological Modelling
(2000) - et al.
Sea-level change along the Italian coast for the past 10,000 yr
Quaternary Science Reviews
(2004) Explaining global patterns of language diversity
Journal of Anthropological Archaeology
(1998)- et al.
Climatic reconstruction in Europe for 18,000 yr BP from pollen data
Quaternary Research
(1998)
H4 abrupt event and late Neanderthal presence in Iberia
Earth and Planetary Science Letters
Absolute calibration of the Greenland time scale: Implications for Antarctic time scales and for Δ14C
Quaternary Science Reviews
Effects of sample size on accuracy of species distribution models
Ecological Modelling
A signal, from human mtDNA, of postglacial recolonization in Europe
American Journal of Human Genetics
mtDNA analysis reveals a major late Paleolithic population expansion from southwestern to northeastern Europe
American Journal of Human Genetics
Distinguishing between tectonic and periglacial deformations of quaternary continental deposits in Europe
Global and Planetary Change
Analysis of Genetic Algorithm for Rule-Set Production (GARP) modeling approach for predicting distributions of fleas implicated as vectors of plague, Yersinia pestis, in California
Journal of Medical Entomology
Geographical distributions of spiny pocket mice in South America: insights from predictive models
Global Ecology and Biogeography
Sea level at 8 and 22 ka cal BP along the Italian coastline
Eco-cultural niche modeling: new tools for reconstructing the geography and ecology of past human populations
PaleoAnthropology
Time as a clue to cause?
Proceedings of the British Academy
Constructing Frames of Reference: An Analytical Method for Archaeological Theory Building Using Hunter-Gatherer and Environmental Data Sets
Seasonal Reconstructions of the Earth's Surface at the Last Glacial Maximum. Map Chart Series MC-36
Latitudinal patterns and environmental determinants of recent human cultural diversity: do humans follow biogeographical rules?
Evolutionary Ecology Research
Evidence for general instability of past climate from a 250 kyr ice-core record
Nature
The human presence in Europe during the last glacial period III: site clusters, regional climates, and resource attractions
Démographie et occupation de l'espace au Paléolithique supérieur et au Mésolithique en France
Préhistoire Européene
Contrasting atmospheric and climate dynamics of the last-glacial and holocene periods
Nature
L'impact de la variabilité climatique rapide des OIS3–2 sur le peuplement de l'Europe
Climate change and evolving human diversity in Europe during the last glacial
Philosophical Transactions of the Royal Society of London B: Biological Sciences
The archaeological and genetic foundations of the European population during the late glacial: implications for ‘agricultural thinking’
Cambridge Archaeological Journal
Geography and evolution
Ecology
Fourth international workshop of the Palaeoclimate Modelling Intercomparison Project (PMIP): launching PMIP phase II
EOS
Climate reconstruction of the Weichselian Pleniglacial in northwestern and central Europe
Journal of Quaternary Science
Concluding remarks
Cold Spring Harbor Symposium on Quantitative Biology
An Introduction to Population Ecology
Irregular glacial interstadials recorded in a new Greenland ice core
Nature
High-resolution simulations of the last glacial maximum climate over Europe: a solution to discrepancies with continental palaeoclimatic reconstructions?
Climate Dynamics
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