El Niño frequency threshold controls coastal biotic communities.

El Niño has profound influences on ecosystem dynamics. However, we know little about how it shapes vertebrate faunal community composition over centennial time scales, and this limits our ability to forecast change under projections of future El Niño events. On the basis of correlations between geological records of past El Niño frequency and the species composition of bird and fish remains from a Baja California bone deposit that spans the past 12,000 years, we documented marked faunal restructuring when major El Niño events occurred more than five times per century. This tipping point has implications for the past and future ecology of eastern Pacific coastal environments.

Climate and demography drive 7000 years of dietary change in the Central Andes.

Explaining the factors that influence past dietary variation is critically important for understanding changes in subsistence, health, and status in past societies; yet systematic studies comparing possible driving factors remain scarce. Here we compile the largest dataset of past diet derived from stable isotope δ13C‰ and δ15N‰ values in the Americas to quantitatively evaluate the impact of 7000 years of climatic and demographic change on dietary variation in the Central Andes. Specifically, we couple paleoclimatic data from a general circulation model with estimates of relative past population inferred from archaeologically derived radiocarbon dates to assess the influence of climate and population on spatiotemporal dietary variation using an ensemble machine learning model capable of accounting for interactions among predictors. Results reveal that climate and population strongly predict diet (80% of δ15N‰ and 66% of Î´13C‰) and that Central Andean diets correlate much more strongly with local climatic conditions than regional population size, indicating that the past 7000 years of dietary change was influenced more by climatic than socio-demographic processes. Visually, the temporal pattern suggests decreasing dietary variation across elevation zones during the Late Horizon, raising the possibility that sociopolitical factors overrode the influence of local climatic conditions on diet during that time. The overall findings and approach establish a general framework for understanding the influence of local climate and demography on dietary change across human history.