Monday, July 5, 2010

Anasazi on the run

In the latest edition of Ecology and Society I published a paper on an agent-based model that aims to understand the resilience of ancient societies in the American South-west. Many of those societies have dissappeared before Europeans colonized America, and the question is why? One of the most popular hypothesis is that a drought caused the abandonement of build settlements. However, this does not explain why other societies persisted during the same period.
During the last 5 years we had a project at ASU where archaeologists, working together with scholars of other disciplines, try to unravel this puzzle. The upcoming special issue in Ecology and Society is a report from that project.
The paper I published is a very stylized model based on my condensation of the discussions I had with archaeologists on the motivations of people to produce food, share, store, exchange, stay or not in their settlement, etc. As a result we have a simple population model for which we can explore the consequences of disturbances. Although the environment is artificial we used rainfall data of the ancient southwest as input time series. The model results suggest that climate variability leads to abandonment of small settlements but increase the long term resilience of the larger area. People are kicked out of settlements by climate shocks, and prevent the soils to erode severely. The soils can recover after abandonment and be occupied later. As such climate variability is not the sole explanation for the abandonement of the large areas in the American southwest. Future work may extent the institutional arrangements to maintain resources. We now had included sharing, exchange, and storage of families, but we did not include group decision making and strategic behavior.