Nonequilibrium dynamics in models of human palaeoecology

Palaeoecological modelling has become significantly more accessible to archaeologists in recent years. New open datasets—high resolution global climate and environmental surfaces (e.g. WorldClim2, MERRAClim, CHELSA, SoilGrids), downscaled palaeoclimate reconstructions from global circulation models (e.g. PaleoView, PaleoClim), and global biodiversity catalogues (e.g. GBIF)—provide both more precise training data and wider spatial and temporal coverage than previously available. At the same time, the increasing availability of R packages for complex modelling tasks allows us to integrate models of discrete elements of the ecological system (climate, plants, animals, humans) within a single framework.

Yet these palaeoenvironmental datasets are relatively static, representing time-averaged reconstructions at a coarse spatial resolution, or “snapshots” of contemporary conditions with a shallow time depth. In reality, many ecosystems are characterised as much by variability and unpredictability as they are by their average trend. In drylands in particular, plants and animals must adapt to this unpredictability, introducing an element of instability to their ecological dynamics that contradicts the ‘equilibrium assumption’ of temperate ecosystems, and which is often overlooked in models of prehistoric human ecology. By contrast, ecologists increasingly recognise the importance of nonequilibrium dynamics in contemporary socioecological systems, where human settlement is conditional on strategies that are resilient to unpredictable environmental conditions (Briske et al. 2017).

In this paper, I will sketch some strategies for incorporating nonequilibrium dynamics into models of human palaeoecology, using as a case study Terminal Pleistocene/Early Holocene foraging societies in the Azraq basin, in the arid margin of the eastern Levant. Based on a combined model of palaeoclimate, vegetation, fauna, and human subsistence, I argue that nonequilibrium dynamics are key to understanding how foragers survived and thrived in this landscape, where resources were scarce and unpredictable. Environmental instability, manifested at multiple scales, shaped the plant and animal resources available to region’s prehistoric societies, and in turn must have necessitated human subsistence strategies adapted to variability and risk. The results indicate that, although they add a layer of computational complexity, nonequilibrium dynamics may be important in understanding human ecological choices in other environments characterised by high variability.