Diverse responses of vegetation and fire after pleistocene megaherbivore extinction across the eastern US
Diverse responses of vegetation and fire after pleistocene megaherbivore extinction across the eastern US
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DOI：
10.1016/j.quascirev.2022.107696
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发表时间：
2022-10
影响因子：
4
通讯作者：
Angelina G. Perrotti;Christopher A. Kiahtipes;J. Russell;S. T. Jackson;J. Gill;G. Robinson;Teresa R. Krause;John W. Williams
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文献类型：
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作者：
Angelina G. Perrotti;Christopher A. Kiahtipes;J. Russell;S. T. Jackson;J. Gill;G. Robinson;Teresa R. Krause;John W. Williams
大型食草动物是关键物种，其从景观中的去除可能导致级联生态系统的变化，但晚第四纪大型食草动物的灭绝的后果仍然不确定。本文检验了巨型食草动物释放假说（MRH），该假说认为，在北美东部末次冰消期，巨型食草动物（体型>1000 kg）的减少和灭绝导致了更可口的硬木树类群的扩张，没有现代类似物的植被组合的发展，以及燃料负荷和火灾活动的增加。粪真菌孢子在湖泊沉积物记录被用来作为代理megaherbivore丰富和必不可少的测试MRH通过分析植被组成，megaherbivore丰富，火灾和气候之间的铅/滞后关系。虽然先前对个别地点粪生真菌孢子的分析支持MRH，但这些解释因以下因素而变得复杂：1）粪生孢子减少的时间与基于过时脊椎动物遗骸的大型草食动物灭绝时间的差异，2）依赖于单一真菌分类群（Sporormiella），而不是一套完整的粪生真菌类群，和3）在影响真菌孢子丰度的埋藏过程中的不确定性。为了研究巨型草食动物，植被和火灾之间的时空关系，我们开发了五个新的多类群粪生真菌孢子记录与现有的花粉，孢子和木炭记录在北美东部的14个地点进行比较。MRH在美国东北部和中部得到了很好的支持，大多数地点显示粪生孢子减少了14.6 ka，其次是硬木类群的增加（14.4 ka）。然而，在火制度的变化有很大的不同东北部和美国中部的网站，并可能之前孢子下降。在美国东南部，MRH没有得到很好的支持，在那里，硬木类群（16.1-13.1 ka）的小幅上升通常先于粪生孢子在个别地点（15.8-12.7 ka）的下降。这些站点水平和区域差异表明晚第四纪megaherbivorescences，植被组成和结构，以及火灾制度之间的耦合强度的空间变化。对美国北方和东南部之间差异的可能解释包括：（1）冠层开放度和适口性的景观异质性差异，（2）净初级生产力和对自上而下营养效应的敏感性，（3）巨型草食动物密度，（4）从轨道到千年时间尺度的气候趋势和季节性。
Megaherbivores are keystone species whose removal from landscapes can cause cascading ecosystem changes, yet the consequences of Late Quaternary megaherbivore extinctions remain uncertain. This paper tests the Megaherbivory Release Hypothesis (MRH), which posits that the decline and extinction of megaherbivores (body size >1000 kg) during the last deglaciation in eastern North America contributed to the expansion of more palatable hardwood tree taxa, the development of vegetation assemblages with no modern analogue, and increased fuel load and fire activity. Coprophilous fungal spores in lake sediment records are used as proxies for megaherbivore abundance and are essential to testing the MRH through analyses of lead/lag relationships among vegetation composition, megaherbivore abundance, fire, and climate. Although some prior analyses of coprophilous fungal spores from individual sites have supported the MRH, these interpretations have been complicated by 1) discrepancies in the timing of coprophilous spore declines versus megaherbivore extinction timing based on dated vertebrate remains, 2) reliance on a single fungal taxon (Sporormiella) rather than a full suite of coprophilous fungi taxa, and 3) uncertainties in the taphonomic processes that influence fungal spore abundances. To examine the spatiotemporal relationships among megaherbivory, vegetation, and fire, we developed five new multi-taxon coprophilous fungal spore records for comparison with existing pollen, spore, and charcoal records from 14 sites across eastern North America. The MRH was well supported in the northeast and central US, with most sites showing a coprophilous spore decline by ∼14.6 ka followed by a rise of hardwood taxa (∼14.4 ka). However, changes in fire regime varied widely among northeast and central US sites and may have preceded spore declines. The MRH was not well supported in the southeastern US, where a smaller rise in hardwood taxa (∼16.1–13.1 ka) generally preceded the decline in coprophilous spores at individual sites (∼15.8–12.7 ka). These site-level and regional differences suggest spatial variations in the strength of couplings among late-Quaternary megaherbivore extinctions, vegetation composition and structure, and fire regime. Possible explanations for the differences between the northern and southeastern US include (1) differences in landscape heterogeneity of canopy openness and palatability, (2) net primary productivity and sensitivity to top-down trophic effects, (3) megaherbivore density, and (4) climate trends and seasonality at orbital to millennial timescales.