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.