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Assessing indicators of population size and causes of extinction in late Quaternary megafauna

  • Author(s): Spano, Nicholas George
  • Advisor(s): Barnosky, Anthony D
  • et al.
Abstract

Megafauna are ecologically important. They are ecosystem engineers that substantially modify modern ecosystems, and likely did so for prehistoric ecosystems prior to the Late Quaternary extinction (LQE) event as well. The LQE resulted in the loss of ~65% of all large mammals during an age of global climate change and human population expansion. This means that understanding the causes and ecological impacts of megafauna preceding, during, and following the LQE is important for better understanding megafauna ecology and conservation today.

To further this understanding, here I 1) explore the developing body of indicators used for inferring historic and prehistoric megafauna abundances; 2) investigate the environmental conditions surrounding human arrival and megafauna extirpation in Brazil, and; 3) test how sensitive the Sporormiella megafauna indicator is to temperature and humidity, as these factors could confound megafaunal population-size estimates based on Sporormiella abundances.

The first chapter reviews the many different population-size indicators used in megafauna paleoecology. and finds all have their pros and cons regarding their applicabilities towards reconstructing megafauna populations depending on the depositional environment and other taphonomic factors. A widely used indicator of relative megafauna population size is the abundance of the dung fungus Sporormiella in sediment records, despite the need for more taphonomic work necessary to more robustly relate spore abundance to megafauna abundance.

The second chapter untangles the relationship between climate, vegetation changes, human population growth, and megafauna decline surrounding the LQE in Brazil as a case study. I found that combinations of anthropogenic, climatic, and vegetational changes are likely implicated as causal factors, but the tree factors vary in their importance for different regions of Brazil. However, human population growth prior to the megafauna extirpation stands out as most notable.

The third chapter reports results of an experiment that tested the effects of temperature and relative humidity on Sporormiella growth. I found that humidity above 89% does not notably affect Sporormiella growth but temperature in the range of 10-40 o C is important.

In sum, this means that there is room for development of megafauna indicators, nuances between how different LQE causes can be distinguished at finer spatial scales, and reason to suggest that past climate change may bias Sporormiella -based reconstructions of megafauna populations.

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