地景動態決定了地球生物多樣性的演變過程

 原文網址：https://www.sydney.edu.au/news-opinion/news/2023/11/30/landscape-dynamics-determine-evolution-biodiversity-nature-salles.html

今日發表在《自然》(Nature)的新研究顯示從地質時間尺度來看，河川、高山、海洋與沉積物養分的移動過程，是地球生物多樣性演變的主要動力來源。

過去5億4千萬年沉積物進到海洋的通量(粉紅線)vs海洋動物多樣性(黑線)。兩者之間有顯著的相關性(線上標註的為滅絕事件)。圖片來源：《自然》

巨獸消失，野火遍起

 原文網址：https://news.yale.edu/2021/11/25/loss-ancient-grazers-triggered-global-rise-fires

By Bill Hathaway

距今50000年至6000年前，全世界許多體型龐大的動物都滅亡了，包括生活在草原、極為代表性的食草者(grazer)：長毛象、巨型野牛、古馬……等。由耶魯大學主持，發表在期刊《科學》(Science)的新研究指出，這些食草動物消失引發了全世界草原的野火活動劇烈增加。

這幅Rudolph F. Zallinger的壁畫描繪了猛瑪象生活的年代。(圖片來源：耶魯大學皮博迪自然史博物館，2016)

恐龍在滅亡之前已邁入衰敗

 原文網址：http://www.bristol.ac.uk/news/2021/june/dinosaurs-in-decline-.html

恐龍在6600萬年滅亡的原因是一顆巨大的小行星撞擊地球。然而，古生物學家之間仍持續爭論著恐龍在撞擊之前是否就已經逐漸衰亡。

圖表顯示在恐龍活著的最後一千萬年，種化速率(藍線)有所下降，滅絕速率(紅線)則快速上升。兩者結合之後可以得出物種數目(黑線)，顯示在6600萬年前的小行星撞擊事件不久之前，恐龍的種類就已經快速減少。圖片來源：Fabien L. Condamine

科學家在非洲最新發現的「蹺蹺板型氣候」驅動了人類演化

 原文網址：https://www.shh.mpg.de/2005624/kaboth-bahr-scerri-african-climate-seesaw?c=1935799

科學家在非洲最新發現的「蹺蹺板型氣候」驅動了人類演化

德國波茨坦大學的Stefanie Kaboth-Bahr博士領導的科學團隊，發現過去有種類似聖嬰現象的氣候模式，主導了撒哈拉以南的非洲過去62萬年的環境變化，這段期間也是人類演化史上的重要時期。之前科學家較常認為人類演化與冰期―間冰期循環有一定的關聯，但團隊發現這個氣候模式對古代撒哈拉以南的非洲造成的影響要來得更大。

研究人員主張低緯度的氣候作用掌管了非洲西部和東部動植物的演化與擴散過程，方法是透過增加資源豐富的環境與穩定的生態過度帶，一般認為這些環境條件對於早期人類來說也很重要。圖片來源：Hans Sell

地球植被的變化速度是最近18000年以來的新高

 原文網址：https://news.wisc.edu/earths-vegetation-is-changing-faster-today-than-it-has-over-the-last-18000-years/

By Eric Hamilton

10000年前左右，冰層最近一次大量消融時地球的植被發生了快速的變化。對於全球花粉化石的調查結果發現地球植被目前的變化速度至少和當時一樣快。

為了研究過去的植物生態系與它們的變化過程，研究人員前往湖泊或者其他適合的環境來鑽取岩芯，這些層層堆疊的沉積物裡通常含有數千年來不斷堆積下來的花粉顆粒。接下來，透過鑑定並計算裡面不同種類的花粉顆粒有多少，研究人員可以重建當地的植被組成。最後，利用花粉豐度隨著時間的變化，就能估計出植被的變化速率。圖片繪自Milan Teunissen Van Manen

過去有多少隻暴龍？數十億吧

 原文網址：https://news.berkeley.edu/2021/04/15/how-many-t-rexes-were-there-billions/

By Robert Sanders

白堊紀時有多少隻暴龍漫步在北美洲？

根據加州大學柏克萊分校的研究，北美洲在250萬年當中總共出現了25億隻暴龍，只有非常小的一部分被古生物學家挖掘出來並加以研究。(圖片來源：Julius Csotonyi/Science magazine)

希克蘇魯伯撞擊事件創造出現代的雨林

 原文網址：https://stri.si.edu/story/flowers

6600萬年前，一顆巨大的小行星撞上今日的猶加敦半島，造成地球陷入一片黑暗當中。但是這場撞擊事件也改變了熱帶雨林，促使花朵得以稱王。

青少年的「霸王龍」是否淘汰了其他恐龍？

 原文網址：http://news.unm.edu/news/did-teenage-tyrants-outcompete-other-dinosaurs

研究人員探討肉食性恐龍的後代如何減少物種多樣性

新墨西哥大學和內布拉斯加大學林肯分校的古生態學家，證明霸王龍這類巨型肉食性恐龍的後代可能會淘汰其他與之競爭的較小型物種，因此徹底重新改造了牠們所處的群集。

恐龍體型分布出現的空缺v.s.現代的肉食性哺乳類。圖片來源：UNM Newsroom

造成恐龍難以在地球生存的原因是小行星撞擊，而非火山爆發

原文網址：https://www.imperial.ac.uk/news/198595/asteroid-impact-volcanoes-made-earth-uninhabitable/

造成恐龍難以在地球生存的原因是小行星撞擊，而非火山爆發

by Hayley Dunning

模擬6600萬年前的希克蘇魯伯小行星撞擊事件之後，結果顯示地球大部分地方因此變得不適合恐龍生存。

在小行星撞擊而滅絕之前，恐龍仍然相當繁榮

原文網址：https://www.imperial.ac.uk/news/190446/dinosaurs-were-thriving-before-asteroid-strike/

在小行星撞擊而滅絕之前，恐龍仍然相當繁榮

By Hayley Dunning

在小行星撞擊而突然消失之前，恐龍仍然相當繁榮，並未受到長期氣候變遷的影響。

重建麥斯特里希特期(6600萬年前)北美大陸的古環境。生活這片氾濫平原上的恐龍有暴龍、埃德蒙頓龍、三角龍等。圖片來源：Davide Bonadonna

人類祖先並非古代非洲哺乳類滅絕的元兇

原文網址：https://unews.utah.edu/human-ancestors-not-to-blame-for-ancient-mammal-extinctions-in-africa/

人類祖先並非古代非洲哺乳類滅絕的元兇

新研究發現最近460萬年以來草原擴張造成大型哺乳類逐漸減少

有個歷時已久的說法認為最近數百萬年來非洲大型哺乳類逐漸滅絕，是由我們最早會使用工具的祖先造成。不過一項新的研究對此提出質疑；反之，他們主張長期的環境變遷，主要是草原的擴張才是哺乳類滅絕的元兇。而環境變遷可能是由大氣二氧化碳濃度下降所造成。

肯亞西部挖出的河馬(Hippopotamus amphibius，左)和白犀牛(Ceratotherium simum，右)牙齒化石，年代為更新世晚期。這兩種動物是現存為數不多的巨型草食動物(megaherbivore)。來源：J. Tyler Faith

地球最古老的動物組成了複雜的生態群集

原文網址：https://news.vanderbilt.edu/2018/09/17/earths-oldest-animals-formed-complex-ecological-communities/

地球最古老的動物組成了複雜的生態群集

Heidi Hall

謎樣的埃迪卡拉生物群(Ediacara biota)生活在5.7億至5.4億年前，是地球第一批肉眼可見的動物。一項新的分析結果使我們對牠們有了更深的理解。

Darroch最近於納米比亞進行研究時發現了這些埃迪卡拉生物群的化石。圖片來源：Simon A.F. Darroch

地球上的生物體型首次變大的原因為何？

原文網址：http://www.cam.ac.uk/research/news/why-life-on-earth-first-got-big

地球上的生物體型首次變大的原因為何？

地球上某些最早期的複雜生物――同時可能也是最早出現的動物――體型增加的原因並非是為了競爭食物，而是想要盡可能地把後代散佈到遠方。

古代的全球冷化事件造就了當代生態系

原文網址：www.sciencedaily.com/releases/2016/09/160930144424.htm

古代的全球冷化事件造就了當代生態系

大約7百萬年前，全球各處的地貌及生態系統開始發生了劇烈變化。非洲的副熱帶地區越趨乾燥，導致撒哈拉沙漠形成。雨林在南北美、非洲和亞洲的面積減少，直到今日仍被廣大的莽原和草原取代。

目前為止，通常以互不相關的構造運動，像是山脈隆起或海盆變化，各自造成局部地區的氣候變化來解釋上述事件。但在一項新研究中，研究人員發現這些環境變遷跟一起先前無文獻紀載的全球冷化事件正好同期。它的成因可能是因大氣二氧化碳含量銳減而造成。

由布朗大學的地質學家領導，發表在期刊《自然―地質科學》(Nature Geoscience)的研究，主要立論於一段新建立起來的全球海溫紀錄，其區間橫跨了過去1200萬年。紀錄顯示在700萬至540萬年前的中新世(Miocene)末，有段時期海洋表面溫度特別的低。中新世全球氣候據信是比現在還要溫暖許多，但在這篇研究中發現的寒冷時期，海洋表面溫度卻驟降到近似於現在的數值。

「這是第一次有全球海洋表層溫度記錄將中新世晚期納入其中，而我們從中發現的溫度下降幅度連我們自己也感到相當驚訝。」領導此研究的布朗大學地球、環境與行星科學系的教授Timothy Herbert表示。「有了這段溫度變化，於此時開始發生的古生物學現象便開始顯得合理許多。」

這項新的海洋表面溫度紀錄源自於從世界各地17個不同地點採集的海洋沉積物樣品。當中含有一種浮游生物的遺骸，其細胞化學物質會依據溫度高低而產生變化。科學家測量這種對溫度敏感的分子含量多寡，便能重新建構溫度如何隨時間改變。

從南北半球各個海盆採取的樣品中都能偵測到在中新世晚期有段寒冷時期。冷化幅度越往兩極就越強烈，而往赤道則較緩和。Herbert說這種模式代表氣溫下降是由全球大氣發生變化所導致，最有可能的嫌疑犯便是二氧化碳(CO₂)。

「這起冷化事件具有兩半球對稱且在高緯度較為劇烈的特性―這些都是跟二氧化碳相關的溫度變化會留下的特徵。」Herbert說。「由於我們無法直接測量二氧化碳，因此不能證明其濃度有下降，但我們的確找到了二氧化碳濃度降低造成的間接證據。」

研究人員說氣溫降低在中新世末發生的副熱帶越趨乾燥現象中可能具有重大影響。「當地球變得較冷，尤其是海洋溫度降低，會造成大氣中的水氣減少。」Herbert表示，「隨著地球冷化，水循環的速率基本上也會減慢。」

如果大氣二氧化碳含量降低確實驅使了冷化現象發生，那麼這就能解釋為何在中新世晚期全球植被組成產生了劇烈改變，也就是南北美、亞洲和非洲副熱帶地區的森林轉變成草原或莽原。時至今日這些地區仍以此種生態系為主。在非洲，草原和莽原棲地出現可能跟早期人類祖先的演化有所關聯。

在這段時期開始佔據主流地位的草本植物為「四碳」植物(C4 plant)。它們行光合作用的路徑跟樹木和其他植物有些微不同，造成四碳路徑在低二氧化碳的環境條件中可以行使得更有效率。「如果當時二氧化碳濃度變得較低，就比較利於這些四碳植物生存。」Herbert說，「因此我們可以將植被轉變的原因和造成中新世末期冷化事件的可能成因連結至同一現象。」

Herbert表示現在還不清楚是什麼導致了二氧化碳濃度降低。有可能是當時發生了大規模地質現象而對碳循環產生重大影響。Herbert的實驗室目前正在深入探討這種可能性。

但可以確定的是在中新世末期全球氣溫發生了重大變化。

「現行觀點認為當時的全球氣候並無特別可看之處。」Herbert說，「但從研究結果看來，它其實比人們以往認為的還要有趣許多。」

Ancient global cooling gave rise to modern ecosystems

Around 7 million years ago, landscapes and ecosystems across the world began changing dramatically. Subtropical regions dried out and the Sahara Desert formed in Africa. Rain forests receded and were replaced by the vast savannas and grasslands that persist today in North and South America, Africa and Asia.

Up to now, these events have generally been explained by separate tectonic events -- the uplift of mountain ranges or the alteration of ocean basins -- causing discrete and local changes in climate. But in a new study, a team of researchers has shown that these environmental changes coincided with a previously undocumented period of global cooling, which was likely driven by a sharp reduction in atmospheric carbon dioxide.

The research, led by a Brown University geologist and published in Nature Geoscience, is based on a newly developed record of global sea surface temperatures spanning the past 12 million years. The record reveals a distinct period of cooler sea surface temperatures spanning 7 million to 5.4 million years ago, the end of the Miocene epoch. The global climate during the Miocene is known to have been much warmer than the present. During the cool period detected in this study, sea surface temperatures dropped to near modern levels.

"This is the first time the late Miocene has been put in a context of global sea surface temperatures, and we were surprised to see the amount of cooling we found," said Timothy Herbert, professor in the Department of Earth, Environmental and Planetary Sciences at Brown, who led the study. "In light of this temperature change, the paleobiological observations from this period start to make a lot more sense."

The new record of sea surface temperatures was derived from ocean sediment sampled at 17 different sites around the world. The sediment preserves the remains of a plankton species that varies cellular chemistry with temperature. By measuring amounts of those temperature-sensitive molecules, scientists can recreate temperature through time.

The late Miocene cool period was detected at every site sampled, in both hemispheres and in every ocean basin on the planet. The cooling was strongest toward the poles and more moderate toward the equator. That pattern, Herbert says, suggests a global atmospheric cause for the temperature decline. The most likely suspect is carbon dioxide (CO₂).

"The hemispheric symmetry and the fact that cooling is much greater at the high latitudes -- these are the fingerprints of CO₂-related temperature change," Herbert said. "We haven't proven that it was a decline in CO₂ because we're not measuring it directly, but we're making a circumstantial case for a reduction in CO₂."

The cooler temperatures would likely have played a role in the drying of the subtropics in the late Miocene, the researchers say. "A cooler world -- particularly a cooler ocean -- would have decreased moisture in the atmosphere," Herbert said. "The hydrological cycle basically slows down with cooling."

And if the cooling was indeed driven by a reduction in atmospheric CO₂, it could explain a critical shift in global vegetation that occurred during the late Miocene: the transition from forests to grassland and savanna in the subtropical regions of North and South America, Asia and Africa. These ecosystems are still present today. In Africa, these are the habitats associated with the evolution of our early human ancestors.

Many of the grassy plant species that began thriving during this period are "C4" plants. These species use a slightly different photosynthetic pathway than trees and other plants. The C4 pathway is more efficient in low CO₂ environments. "It could be that that if CO₂ declined, these C4 species were favored," Herbert said. "So we can associate that shift in vegetation with the same thing that we suspect was driving the late Miocene cooling."

It isn't clear at this point what might have driven a reduction in CO₂ during this period, Herbert says. It could be that there were large-scale geological changes occurring at this time that affected the carbon cycle. Herbert's lab is looking into that possibility now.

But what is clear is that there was a significant global shift in global temperatures during the late Miocene.

"The prevailing view was that this wasn't a particularly exciting time in terms of global climate," Herbert said. "It turns out to be more interesting than people thought."

原始論文：Timothy D. Herbert, Kira T. Lawrence, Alexandrina Tzanova, Laura Cleaveland Peterson, Rocio Caballero-Gill, Christopher S. Kelly. Late Miocene global cooling and the rise of modern ecosystems. Nature Geoscience, 2016; DOI:10.1038/ngeo2813

引用自：Brown University. "Ancient global cooling gave rise to modern ecosystems." ScienceDaily. ScienceDaily, 30 September 2016. 

沒有人類，整個世界也許看起來就像塞倫蓋蒂(Serengeti)般的生機盎然

原網址：www.sciencedaily.com/releases/2015/08/150820212652.htm

Without humans, the whole world could look like Serengeti

沒有人類，整個世界也許看起來就像塞倫蓋蒂(Serengeti)般的生機盎然

New study shows what the natural worldwide diversity patterns of mammals would be like in the absence of past and present human impacts

新的研究顯示出若沒有過去與現在的人類影響，自然世界中哺乳類的多樣性應該如何分佈

The fact that the greatest diversity of large mammals is found in Africa reflects past human activities -- and not climatic or other environmental constraints. This is determined in a new study, which presents what the world map of mammals would look like if modern man (Homo sapiens) had never existed.

在這篇新研究中，研究人員呈現出若現代人(Homo sapiens)從未出現，哺乳類在這個世界上應是如何分佈。他們的結果顯示非洲擁有最高的大型哺乳類多樣性，反映出來的是過往人類活動的影響，而非氣候或其他環境限制導致。

In a world without humans, most of northern Europe would probably now be home to not only wolves, Eurasian elk (moose) and bears, but also animals such as elephants and rhinoceroses.

在沒有人類的世界，現今北歐大部分的地區可能不只是狼、歐亞駝鹿(麋鹿)與熊的家園，也會有其它動物生活於此，像是大象與犀牛。

This is demonstrated in a new study conducted by researchers from Aarhus University, Denmark. In a previous analysis, they have shown that the mass extinction of large mammals during the Last Ice Age and in subsequent millennia (the late-Quaternary megafauna extinction) is largely explainable from the expansion of modern man (Homo sapiens) across the world. In this follow-up study, they investigate what the natural worldwide diversity patterns of mammals would be like in the absence of past and present human impacts, based on estimates of the natural distribution of each species according to its ecology, biogeography and the current natural environmental template. They provide the first estimate of how the mammal diversity world map would have appeared without the impact of modern man.

此幅景象呈現於丹麥奧胡斯大學(Aarhus University)的研究人員新進行的研究結果之中。在先前的分析當中，他們已經顯示在上次冰河期以及之後數千年間，發生的大型哺乳類滅絕事件(晚第四紀巨型動物群滅絕事件，the late-Quaternary megafauna extinction)絕大部分要歸咎於現代人(Homo sapiens)往世界各地遷徙。在這篇後續研究當中，他們根據不同種哺乳類各自的生態、生物地理分佈以及在自然條件下，各地環境應有的樣貌為何，來預測牠們的自然分佈模式，並總和所有結果得出若沒有過去及現今的人類影響，在自然情形下哺乳類多樣性在全世界的分佈模式。他們的結果呈現了首幅在沒有現代人的影響下，哺乳類多樣性會如何分佈的世界地圖。

"Northern Europe is far from the only place in which humans have reduced the diversity of mammals -- it's a worldwide phenomenon. And, in most places, there's a very large deficit in mammal diversity relative to what it would naturally have been," says Professor Jens-Christian Svenning, Department of Bioscience, Aarhus University, who is one of the researchers behind the study.

「北歐絕不是唯一人類導致哺乳類多樣性下降的地區─這是一個在全世界都相當普及的現象。而且在多數地區，哺乳類多樣性跟在自然背景下應有的相比，都下降了非常多。」此篇研究的作者之一，奧胡斯大學生命科學系的教授Jens-Christian Svenning說。

Africa is the last refuge

非洲─最後的淨土

The current world map of mammal diversity shows that Africa is virtually the only place with a high diversity of large mammals. However, the world map constructed by the researchers of the natural diversity of large mammals shows far greater distribution of high large-mammal diversity across most of the world, with particularly high levels in North and South America, areas that are currently relatively poor in large mammals.

現今的哺乳類多樣性世界地圖顯示出非洲為僅存大型哺乳類仍具有高度多樣性的地區。然而，由研究人員建立的世界地圖卻顯示在自然情況下，具有高度大型哺乳類多樣性的地區廣泛分佈於世界各地。其中又以南北美洲為特別高的地區，儘管目前這些地方的大型哺乳類相對來說相當罕見。

"Most safaris today take place in Africa, but under natural circumstances, as many or even more large animals would no doubt have existed in other places, e.g., notably parts of the New World such as Texas and neighboring areas and the region around northern Argentina-Southern Brazil. The reason that many safaris target Africa is not because the continent is naturally abnormally rich in species of mammals. Instead it reflects that it's one of the only places where human activities have not yet wiped out most of the large animals," says Postdoctoral Fellow Soren Faurby, Department of Bioscience, Aarhus University, who is the lead author on the study.

「現今的遊獵(safari，原本意指以狩獵大型動物為主的遠行活動，現在多已轉變成觀光性質)多半僅見於非洲，但在自然條件下，毫無疑問地會有同樣多數量，甚至更大批的大型動物生存在其他地區，譬如說目前新世界的都會區，如德州與其鄰近區域，以及阿根廷部北部至巴西南部地區。許多遊獵選在非洲並非因為當地本來就擁有特別多種的哺乳類，而是反應出非洲為人類活動尚未殲滅大部分大型哺乳類的僅存地區之一。」本篇研究的第一作者，奧胡斯大學生命科學系的博士後研究員Soren Faurby說。

The existence of Africa's many species of mammals is thus not due to an optimal climate and environment, but rather because it is the only place where they have not yet been eradicated by humans. The underlying reason includes evolutionary adaptation of large mammals to humans as well as greater pest pressure on human populations in long-inhabited Africa in the past.

因此非洲擁有許多種哺乳類的原因並非是其擁有特別宜人的氣候以及環境，而是因為它是尚未遭人類染指的最後淨土。這背後的原因包括了當地的大型哺乳類演化出對人類有較高的適應能力，以及長久以來非洲的住人地區因為寄生蟲肆虐，而大幅限制了人口增長。

Better understanding helps nature preservation

瞭解更多有助於生態保育

The study's openly accessible data set of natural range maps for all late-Quatenary mammals provides researchers with the first opportunity to analyse the natural patterns in the species diversity and composition of mammals worldwide. Hereby, it can be used to provide a better understanding of the natural factors that determine the biodiversity in a specific area.

此篇研究提供了所有晚第四紀以來的哺乳動物，在自然條件下應會如何分佈的公開地圖資料，有了這些資料，研究人員首度有機會分析世界各地的哺乳動物多樣性及組成，在僅考慮自然條件下的分佈模式。而這可以讓我們對特定地區的自然因子如何影響當地的生物多樣性有更深入的瞭解。

Today, there is a particularly large number of mammal species in mountainous areas. This is often interpreted as a consequence of environmental variation, where different species have evolved in deep valleys and high mountains. According to the new study, however, this trend is much weaker when the natural patterns are considered.

現今的山區環境有特別多樣的哺乳類。這通常被視作山區能提供各式各樣的環境而造成的結果。生物在高山與深谷中會往不同的方向演化，因而創造出特別高的多樣性。然而根據此篇新研究，在僅考慮自然因素的生物多樣性分佈模式中，這種趨勢並不特別明顯。

"The current high level of biodiversity in mountainous areas is partly due to the fact that the mountains have acted as a refuge for species in relation to hunting and habitat destruction, rather than being a purely natural pattern. An example in Europe is the brown bear, which now virtually only live in mountainous regions because it has been exterminated from the more accessible and most often more densely populated lowland areas," explains Soren Faurby.

「現今的山區擁有相當高的生物多樣性，部分原因來自於高山對生物來說，是躲避人類狩獵以及棲地破壞的避難所，而非純粹由自然因素造成。在歐洲一個很好的例子便是棕熊。棕熊現在僅生存於深山地區，這是因為牠們已難以生活在對人類而言易於抵達且人口密集的平地。」

Hereby, this new study can provide an important base-line for nature restoration and conservation.

此新研究能夠提供未來自然保育與復育的研究上重要的基準點。

The study has been published in the scientific journal Diversity and Distributions.

本研究刊登於科學期刊《生物多樣性與分佈》(Diversity and Distributions)。

The natural diversity of large mammals is shown as it would appear without the impact of modern man (Homo sapiens). The figure shows the variation in the number of large mammals (45 kg or larger) that would have occurred per 100 x 100 kilometer grid cell. The numbers on the scale indicate the number of species.

上圖為在沒有現代人類(Homo sapiens)的影響下，大型哺乳類多樣性的自然分佈模式。將地圖分成100 x 100 公里的網格後，計算每一格當中有多少種大型哺乳類(45公斤以上)而得到此圖。右方刻度代表物種數目。

Credit: Illustration: Soren Faurby

引用自：Aarhus University. "Without humans, the whole world could look like Serengeti: New study shows what the natural worldwide diversity patterns of mammals would be like in the absence of past and present human impacts." ScienceDaily. ScienceDaily, 20 August 2015.