Ecological consequences of Pleistocene megafaunal declines in the Neotropics

项目背景更新世末期的特征是世界范围内大型哺乳动物的灭绝。这些大型哺乳动物也被称为巨型动物，它们的灭绝可能是由气候变化和人类压力共同驱动的（Barnosky et al. 2004）。在世界范围内，巨型动物灭绝的时间在5万到1万年前之间，各大洲之间存在一些差异。大型动物在更新世生态系统中发挥着重要的生态作用，包括种子传播、控制植被结构、调节燃料积累和火灾活动（Gill et al. 2012, Raczka et al. 2018, Hyvarinen et al. 2021）。因此，巨型动物的灭绝被认为对现存的生态系统产生了重大的生态后果（Doughty et al. 2013, Faith et al. 2011）。在南美洲热带地区，尽管估计有85%的巨型动物物种灭绝，但关于这些灭绝的信息仍然有限。当前的全球环境变化正在导致生物多样性丧失，物种面临灭绝的威胁。了解更新世巨型动物灭绝的生态后果对于估计当代灭绝的潜在影响至关重要。由于迄今为止发现的巨型动物化石遗址数量有限，对热带南美洲巨型动物灭绝的研究受到了阻碍。在食草动物粪便上发芽的孢子可以作为估计巨型动物存在和减少的替代方法（Davis & Shafer 2006, Perroti & van Asperen 2019）。粪便孢子很容易与花粉化石和木炭颗粒一起沉积和保存在沉积物中。花粉和木炭可以用来重建植被组成和火灾活动（Urrego et al 2016）。沉积物中常量营养素（C、N、P、K、Ca、Mg和S）浓度的性质、空间分布和分子形态可用于了解环境中养分转移的时间变化（Adediran等人，2021）。总之，这些综合数据集可以提供有关南美热带地区巨型动物灭绝的生态后果和巨型动物减少时间的宝贵信息。项目目标和方法本博士项目将结合来自南美洲热带沉积档案的微化石和空间宏量营养素分析来解决以下问题：1)巨型动物灭绝前的环境环境是什么？2)南美洲热带巨型动物灭绝的时间是什么时候？iii)由于巨型动物的灭绝，植被组成和火灾活动是否发生了变化？iv)过去和现在的土壤宏量养分浓度和物种形成是巨型动物灭绝的结果吗？博士项目还将在南美热带地区的几个地点制作一份巨型动物灭绝及其生态后果的区域综合报告。

Project BackgroundThe 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 MethodsThis 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.