Ecological consequences of Pleistocene megafaunal declines in the Neotropics

Project Background

The end of the Pleistocene period was characterised by the extinction of large mammals worldwide. These large mammals are also known as Megafauna and their extinction was likely driven by a combination of climate change and human pressure (Barnosky et al. 2004). The timing of Megafauna extinctions falls between 50,000 and 10,000 years ago worldwide, with some variability between continents. Megafauna played important ecological roles in Pleistocene ecosystems including seed dispersal, controlling vegetation structure, and regulating fuel build-up and fire activity (Gill et al. 2012, Raczka et al. 2018, Hyvarinen et al. 2021). Megafauna extinctions are therefore thought to have had significant ecological consequences for the ecosystems that remained (Doughty et al. 2013, Faith et al. 2011). In tropical South America, information on these extinctions is limited even though it is estimated that 85% of Megafauna species went extinct. Current global environmental change is driving biodiversity loss and threatening species with extinction. Understanding the ecological consequences of Pleistocene Megafauna extinctions is crucial to estimate the potential repercussions of contemporary extinctions.

The study of megafauna extinctions in tropical South America is hindered by the limited number of Megafauna fossil sites discovered to date. Spores that germinate on herbivore dung can be used as an alternative to estimate Megafauna presence and declines (Davis & Shafer 2006, Perroti & van Asperen 2019). Dung spores are readily deposited and preserved in sediments along with fossil pollen and charcoal particles. Pollen and charcoal can be used to reconstruct vegetation composition and fire activity (Urrego et al 2016). The nature of macronutrient (C, N, P, K, Ca, Mg, and S) concentrations, spatial distributions and molecular speciations in sediments can be used to understand temporal changes in nutrient transfer in the environment (Adediran et al., 2021). Together, these integrated datasets can provide valuable information on the ecological consequences of Megafauna extinctions and the timing of Megafauna declines in tropical South America.

Project Aims and Methods

This PhD project will combine microfossils and spatial macronutrient analysis from sedimentary archives in tropical South America to address the following questions: i) what is the environmental setting prior to Megafauna extinctions?, ii) what is the timing of Megafauna extinctions in tropical South America?, iii) have vegetation composition and fire activity changed as a consequence of Megafauna extinctions? iv) can past and present soil macronutrient concentration and speciation be a consequence of Megafauna extinctions? The PhD project will also produce a regional synthesis of Megafauna extinctions and their ecological consequences across several sites in tropical South America.