Controversy exists over the role of humans and climate in the extinction of South American Pleistocene megafauna. In the Andes, archaeological evidence suggests incursions of hunters and establishment of settlements at high elevations (>4000 m asl) at 12,800 years before present. However, the establishment of human settlements in the High Andes was clearly preceded by climatic instability during the deglaciation observed in tropical South America between 21,000 and 12,800 years. The late human establishment relative to the decline in Sporormiella, a proxy for megafauna, offers the opportunity to potentially differentiate the effects of climate change from human hunting on megafaunal extinction.
Here we present a paleocological reconstruction spanning the last 25,000 years from Lake Pacucha-Peru (3100 m asl) that aims to determine the role of humans and climate in the functional extinction of Pleistocene megafauna in the Peruvian Andes.
We analyzed pollen, charcoal and the dung fungus Sporormiella using Bayesian change point analysis (BCP) and Spearman rank correlation matrices in an attempt to establish the time, causes, and ecological consequences of the megafaunal extinction in the Andes
Results/Conclusions
Results from the BCP analysis showed that the decline in Sporormiella, coincided with the decrease in forbs pollen taxa and the increase in montane arboreal taxa at 16, 900 years ago (posterior probability = 0.92). The second largest posterior probability (0.85) at 12,600 years ago was driven by the decrease of Polylepis, Acalypha and Podocarpus. Additionally, some of the most palatable species (i.e. Lactuceae, Plantago, Lysipomia, Caryophyllaceae and Geraniaceae) were significantly positively correlated with Sporormiella abundance. Conversely, species sensitive to mechanical damage (i.e. Melastomataceae, and Ericaceae) were negatively correlated with Sporormiella abundance. The decline in Sporormiella abundance was followed by increase fire frequency (p=< 0.001, rho= -067).
Our results chronicled a two-stage megafaunal population collapse that coincided with warm and wet events in the Andes. The sudden decrease in Sporormiella abundance at 16,900 years ago indicated that megafaunal populations became functionally extinct in the area at least 4000 years prior human incursion in the high Andes. The decline of megafaunal populations came amid warm, drought-prone intervals, triggering an ecological cascade that resulted in novel floral assemblages, and increases in woody species, fire frequency, and species sensitive to trampling.