Directly modelling population change in the South American Arid Diagonal using 14C dates

ADRIAN TIMPSON; RAMIRO BARBERENA; MARK G. THOMAS; CÉSAR MÉNDEZ; KATIE MANNING

PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES

ROYAL SOC

Lugar: Londres; Año: 2021 p. 1 - 12

0962-8436

Large anthropogenic 14C datasets are widely used to generate summed probability distributions (SPD) as a proxy for past human population levels. However, SPDs are a poor proxy when datasets are small,bearing little relationship to true population dynamics. Instead, more robust inferences can be achieved by directly modelling the population and assessing the model likelihood given the data. We introduce a continuous piecewise linear (CPL) model of population change, calculate the model likelihood for a given 14C dataset, estimate credible intervals using MCMC, and apply a Goodness of Fit test. We utilise the Bayesian Information Criterion (BIC) to compare CPL models and prevent overfitting. We demonstrate the efficacy of this method using toy data to show that spurious dynamics are avoided when sample sizes are small, and true population dynamics are recovered as sample sizes increase. Finally, we use an improved 14C dataset for the South American Arid Diagonal to compare CPL modelling to current simulation methods and identify three Holocene phases when trajectories changed from rapid initial growth of 4.93% per generation to a decline of 0.05% per generation between 10,812 and 7,044 yr BP, then gently grew at 0.58% per generation until 2,500 yr BP.