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Global hunter-gatherer population densities constrained by influence of seasonality on diet composition

Nature Ecology & Evolution volume 5, pages 1536–1545 (2021)Cite this article

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Abstract

The dependence of hunter-gatherers on local net primary production (NPP) to provide food played a major role in shaping long-term human population dynamics. Observations of contemporary hunter-gatherers have shown an overall correlation between population density and annual NPP but with a 1,000-fold variation in population density per unit NPP that remains unexplained. Here, we build a process-based hunter-gatherer population model embedded within a global terrestrial biosphere model, which explicitly addresses the extraction of NPP through dynamically allocated hunting and gathering activities. The emergent results reveal a strong, previously unrecognized effect of seasonality on population density via diet composition, whereby hunter-gatherers consume high fractions of meat in regions where growing seasons are short, leading to greatly reduced population density due to trophic inefficiency. This seasonal carnivory bottleneck largely explains the wide variation in population density per unit NPP and questions the prevailing usage of annual NPP as the proxy of carrying capacity for ancient humans. Our process-based approach has the potential to greatly refine our understanding of dynamical responses of ancient human populations to past environmental changes.

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Fig. 1: Contemporary hunter-gatherer population density versus net primary production.
Fig. 2: Schematic of FORGE, coupled to the ORCHIDEE global terrestrial biosphere model.
Fig. 3: Modelled population density and time allocation.
Fig. 4: Meat fraction of the diet controls ΦNPP.
Fig. 5: Seasonality, diet composition and carbon flows.

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Data availability

The contemporary hunter-gatherer data and environmental variables used in the analysis are available in the Supplementary Data.

Code availability

Source code (in Python) of the FORGE model and its output files (in NetCDF format) for this study, including the three sets of global simulations (S0, S1, S2), are provided in Supplementary Software. The corresponding input files for the FORGE model are available at https://doi.org/10.6084/m9.figshare.14995320.v2.

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Acknowledgements

D.Z. and E.D.G. acknowledge the financial support from the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (agreement no. 682602, to E.D.G.). D.Z. also acknowledges support from the National Natural Science Foundation of China (grant no. 41988101). V.R.-G. acknowledges support from the European Research Council under agreement no. 771056.

Author information

Authors and Affiliations

  1. Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, China

    Dan Zhu

  2. Institut de Ciència i Tecnologia Ambientals (ICTA-UAB), Universitat Autònoma de Barcelona, Barcelona, Spain

    Dan Zhu, Eric D. Galbraith & Victoria Reyes-García

  3. Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec, Canada

    Eric D. Galbraith

  4. ICREA (Catalan Institution for Research and Advanced Studies), Barcelona, Spain

    Eric D. Galbraith & Victoria Reyes-García

  5. Laboratoire des Sciences du Climat et de l’Environnement, IPSL-LSCE, CEA-CNRS-UVSQ-UPSACLAY, Gif sur Yvette, France

    Philippe Ciais

  6. Climate and Atmosphere Research Center (CARE-C), The Cyprus Institute, Nicosia, Cyprus

    Philippe Ciais

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Contributions

D.Z. and E.D.G. conceived the study and model design. D.Z. built the model, performed the analyses and wrote the first draft. E.D.G. provided discussion and suggestions throughout the process. V.R.-G. and P.C. contributed to the interpretation of the results and writing of the manuscript.

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Correspondence to Dan Zhu.

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Peer review information Nature Ecology & Evolution thanks Trevor Fristoe and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–23, Discussion 1–3 and Tables 1–4.

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Supplementary Data

The contemporary hunter-gatherer data and environmental variables used in the analysis.

Supplementary Software

Source code (in Python) of the FORGE model and its output files (in NetCDF format) including the three sets of global simulations (S0, S1, S2).

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Zhu, D., Galbraith, E.D., Reyes-García, V. et al. Global hunter-gatherer population densities constrained by influence of seasonality on diet composition. Nat Ecol Evol 5, 1536–1545 (2021). https://doi.org/10.1038/s41559-021-01548-3

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