TIMING AND CONSEQUENCES OF PLEISTOCENE MEGAFAUNAL POPULATION COLLAPSE IN SOUTH AMERICA

Abstract

A key question for ecologists and paleontologists studying the extinction of the Pleistocene megafauna is: what caused the extinction of these animals? Was the extinction of megafauna caused solely by human-hunting pressure, or was it a consequence of climate change? Could these extinctions be caused by a combination of both factors? Was this wave of extinction temporally uniform across South America? Despite the recent surge of research on this subject, these questions remain largely unanswered. Spores of Sporormiella, a genus of obligate coprophilous fungi, are now widely used to detect mega-herbivore presence and even estimate their abundance in paleoecological reconstructions. However, this proxy has never been tested in neotropical systems. Mud-water interface samples from nine lakes in Southeastern Brazil were collected to validate the accuracy of Sporormiella for detecting the presence of megaherbivores in a tropical context. The sites were chosen based on lake size and basin morphometry. To investigate the paleoecology of megafaunal population collapse, Sporormiella was analyzed in four sites. Two lakes spanning the last ~22 kcal BP were selected in Southeastern Brazil, a region considered to be important for archaeological and paleontological investigations. Two other sites were in the high Andes: Lake Huiñaimarca, in the Altiplano region on the Peru/Bolivia border, with a record that spanned the last ~30 kcal BP, and Lake Llaviucu, in Ecuador, where the critical interval between 14.9 and 9 kcal was investigated. The analysis of the mud-water interface of nine neotropical lakes indicated that spores of Sporormiella are a very sensitive proxy for large herbivore presence, proving to be an important paleoecological proxy measure for identifying the presence, and with appropriate metadata, the abundance of mega-herbivores. The pollen, charcoal, and Sporormiella analysis from the fossil records of the two lakes in Southeastern Brazil depicted a decline of Sporormiella abundance at c. 14.4 kcal BP, with the final extinction occurring between c. 12 and 11.5 kcal BP. No evidence was found of major ecological or climatic events coincident with the loss of megafauna. The data from Southeastern Brazil indicated that the collapse of megafaunal populations were consistent with humans playing a major role in the megafaunal extinction of the region. In the Andes, however, megafauna populations were responding to episodes of climate upheaval. Climatic events, such as the Tauca highstand (between 18 and 14 kcal BP), coincided with a marked decrease in the abundance of Sporormiella spores at Lake Huiñaimarca. However, at Lake Llaviucu the signal of Sporormiella was found to have occurred much later than at Huiñaimarca. At Lake Llaviucu, where fire was a regular component of the landscape from the inception of the lake at 14.6 kcal BP, which indicated early human occupation. Megafaunal populations survived longer that at Lake Huiñaimarca, collapsing only at c. 12.6 kcal BP. Overall, the data revealed that the extinction of the Pleistocene megafauna was very heterogeneous, with some locations responding more to climatic changes than others. Nonetheless, final extinction of the megafauna probably did not occur until c. 12 -10 kcal BP, with strong evidence of co-existence with humans for several millennia.