Discovery Magazine

Last Ice Age Large Mammal Extinction

The Pleistocene megafauna occupied all habitats in the Americas and would have been important in determining flammability, seed dispersal, and plant community composition. One possibility is that the well-documented novel plant communities at the Pleistocene-Holocene boundary were a product of either the activity of megafauna or their sudden loss from the system. A detailed comparison of vegetation types, fire regimes and megafaunal abundance is needed, and is possible through paleoecological proxies. Bush and his research team will investigate five South and Central American regions (a total of 13 lakes) using fossil pollen, charcoal, diatoms and Sporormiella fungal spores, as a proxy for megafaunal abundance, to address research questions concerning the timing and consequences of megafaunal population collapses. The fossil pollen and other proxies will allow Bush to reconstruct the past vegetation surrounding the lake. The team will resolve whether megafaunal population changes occurred before or within the period of human occupation.

Fossil pollen will be used to answer a particular question: What effect did the loss of megafauna have on tropical landscapes? It is possible that through grazing, the megafauna controlled fire frequency. If that is the case, both charcoal and fossil pollen will show significant changes as the megafaunal populations declined.

Although most megafaunal research to date has centered on North America, there are compelling reasons to conduct an investigation of the timing and ecological impact of the equally profound megafaunal extinctions in the Neotropics. A key advantage of pursuing this research in Neotropical settings is that episodes of abrupt climate change and human arrival, which overlap with the timing of the megafaunal extinctions in North America, are temporally discrete in South America - climate changes starts about 9,000 -11,000 years before major human occupations, while the timing of megafaunal population collapse is unresolved.

If climate did play a role in the extinction, precipitation rather than temperature was the probable cause. There were no large thermal reversals between 19,000 and 11,000 cal. yr BP, but there were profound, abrupt changes in precipitation. By selecting sites north and south of the equator, Bush's team will test hypotheses relating abrupt precipitation events to megafaunal loss and changes in fossil pollen signatures as Central America became wet when the southern Neotropics became dry (and vice versa).