External impacts on internal dynamics: Effects of paleoclimatic and demographic variability on acorn exploitation along the Central California coast

Research into human-environment interaction in California prehistory often focuses on either the internal dynamics of adaptive decisions or the external impacts of environmental change. While both processes were surely driving prehistoric variability, integrating these approaches is not altogether straightforward. Here we outline an inclusive approach examining the exploitation of acorn habitats in Central California. Acorns were critically important to many ethnographic groups in Native California, but the intensive use of acorns appears to be a Late Holocene phenomenon. Most research approaches the increased reliance on acorns as a process governed by internal dynamics linked to demographically-driven resource intensification, but there are strong reasons to believe that climatic variability also structured acorn use. Here we link internal and external human-environmental dynamics through a formal behavioral ecological model. This model provides clear predictions that can be used to identify departures from expected internal dynamics linked to external factors driven by paleoenvironmental change. Results show that prehistoric occupation along the central California coast shifts into interior oak-dominated regions with increasing population densities, consistent with model expectations of internally-driven resource intensification. However, acorn use is also affected by climate: foragers are less likely to live in productive acorn habitats during periods of drought. These findings show that neither internal nor external patterns can completely account for variability in prehistoric decisions, but that integrating these through formal ecological models can provide insights into the external impacts on internal dynamics that structure broad patterns in prehistory.