Environmental scenarios for hominin habitats in East Africa during the Plio-Pleistocene (4-1 Ma)

Climate strongly constrains vegetation structure and the availability of surface water, thereby shaping the distribution, quality, and accessibility of resources for mammals, including hominins, over long timescales. Unfortunately, fossil and archaeological archives are discontinuous and biased by preservation and sampling, which limits the use of deterministic or fully probabilistic approaches that typically rely on continuous time series, homogeneous observations, and well-constrained parameters.

To address these constraints, we formalized current knowledge and competing hypotheses on climate–ecosystem linkages into a qualitative, possibilistic dynamic model. This approach was designed to (i) accommodate incomplete and heterogeneous evidence, (ii) make causal assumptions explicit, and (iii) systematically explore the range of environmental trajectories compatible with those assumptions. We implemented this knowledge base within the EDEN (Ecological Discrete Event Network) framework as a set of formal rules « if-then » describing interactions among climate-related variables, vegetation states, and surface-water availability.

It then reconstructed the resulting transition graph linking successive states through admissible event sequences. The resulting scenario ensemble provided a structured view of which combinations of climate, vegetation, and surface-water availability corresponded to feasible system states, which transitions were enabled or disabled by the rule base and its causal constraints, and where key uncertainties in rule definition and variable discretization most strongly affected the inferred habitat dynamics.