Ecological consequences of Pleistocene megafaunal declines in the Neotropics

项目背景更新世末期的特点是全世界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于气候变化和人类压力的共同作用(Barnosky等人)。2004年)。全球巨型动物灭绝的时间介于5万到10000年前，各大洲之间存在一定的差异。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等人)。2012年，raczka等人。2018年，Hyvarinen等人。2021年)。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等人。2013年，Faith等人。2011年)。在热带的南美洲，关于这些物种灭绝的信息有限，尽管据估计85%的大型动物物种已经灭绝。当前的全球环境变化正在推动生物多样性的丧失，并威胁到物种的灭绝。了解更新世大型动物灭绝的生态后果，对于估计当代物种灭绝的潜在影响至关重要。到目前为止，发现的大型动物化石遗址数量有限，阻碍了对热带南美洲大型动物灭绝的研究。在食草动物粪便上萌发的孢子可用于估计大型动物的存在和减少(Davis&Shafer 2006，Perroti&van Asperen 2019)。粪便孢子很容易与化石花粉和木炭颗粒一起沉积并保存在沉积物中。花粉和木炭可用于重建植被组成和火灾活动(Urrego等人，2016)。沉积物中常量营养素(C、N、P、K、Ca、Mg和S)的浓度、空间分布和分子形态的性质可以用来理解环境中养分转移的时间变化(Adediran等人，2021年)。综合起来，这些综合数据集可以提供有关南美洲热带地区大型动物灭绝的生态后果和大型动物数量减少的时间的宝贵信息。项目目标和方法本博士项目将结合南美洲热带沉积档案中的微化石和空间常量营养素分析，以解决以下问题：i)大型动物灭绝之前的环境背景是什么？ii)热带南美洲大型动物灭绝的时间是什么？iii)大型动物灭绝是否会改变植被组成和火灾活动？四)过去和现在的土壤常量营养素浓度和物种形成会不会是大型动物灭绝的结果？博士项目还将对南美洲热带地区的几个地点的巨型动物灭绝及其生态后果进行地区性综合。

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.