Teasing apart the role of late Pleistocene human arrival and megafauna extinction on Amazonian tree composition

At the end of the Pleistocene, tropical forests in South America underwent three drastic changes that are analogous to today: the climate warmed, people populated the region and started to use and domesticate of part of the native forest plants, and the abundance of seed-dispersing megafauna collapsed. Here, we evaluate the impact of these three changes on tree populations in South America, using pollen time series of >80 tree and palm genera across 10 sites collected over a 100,000 yr period spanning the end of the Pleistocene and Holocene, and linking this to genus-specific traits that are indicators of climate responses, usefulness to humans, and dispersal by megafauna. We find no support for consistent effects of climate warming, and find that megafauna-dispersed tree genera increased – instead of decreased – in abundance after megafauna decline, indicating that climate warming and megafauna decline were no major drivers of changes in tree populations. However, we find that edible tree and palm species increased in abundance. These results are consistent with the idea that people favoured tree taxa that were useful for consumption of their large seeds and fruits, and in this way took over the role of lost seed dispersers and artificially increased the abundance of previously megafauna-dispersed tree taxa.