Scientists Should Focus on Changes in Species to Recognize and Avoid a Mass Extinction

科学家们应关注物种的变化以识别和避免大灭绝

When fossils disappear, the world changes. Today’s mass rarity of marine and terrestrial species may already have a mass extinction-like fossil record. Acting to save the fossil record of today by restoring species abundance and range could ensure the stability of the biosphere.

当化石消失时世界在变化。今天海洋和陆地大量的稀有物种可能已经经历过像化石记录那样的大灭绝。恢复物种的丰富和多样性来保存好今天的化石记录，这样的行动可以保证生物圈的稳定性。

New research from Yale University urges scientists to move their focus from species extinction to species rarity in order to recognize, and avoid, a mass extinction in the modern world.

耶鲁大学新的研究正在敦促科学家们将其关注点从物种的消失转向物种的稀有，以便识别并避免现代世界的大灭绝。

Writing in the journal Nature the week of December 16, Yale’s Pincelli Hull and colleagues from the Smithsonian Institution argue that modern extinction rates may be a poor measure of whether we’re in the midst of a mass extinction event today — something many scientists suspect may be happening. Instead, Hull and her co-authors contend, the best way to see a mass extinction in real time is by studying changes in species and ecosystems.

耶鲁大学的宾塞利.赫尔于12月16日在自然杂志上撰稿，她与来自国立博物馆机构的同行们都认为：近代的灭绝速度对于衡量我们今天是否处于大灭绝的过程之中可能不是太靠谱，因为会有许多科学家会对此产生怀疑。相反，赫尔和她的合著者却主张现实中观察大灭绝的最好方法是研究物种和生态的变化。

Earth has experienced more than a dozen mass extinction events, when the great diversity of life on Earth disappeared and was replaced by a flora or fauna often entirely unlike what had come before. The largest of these events (the most recent, which wiped out the dinosaurs, was 66 million years ago) have collectively become known as the “Five Mass Extinctions.” In recent years, Hull says, some have argued that Earth is entering a sixth mass extinction event. It also was the topic of Elizabeth Kolbert’s Pulitzer Prize-winning book, “The Sixth Extinction.”

地球已经历经10多次大灭绝的事件了，当地球上生命的巨大多样性消失，取而代之的是一个植物群或动物群，往往完全不像从前那样。最大的灭绝事件（最近的一次是发生在6600万年前恐龙的灭绝）已被统称为“五大灭绝事件”。赫尔指出，最近几年有些人认为地球正在走入第六次大灭绝。这也是伊丽莎白.科尔伯特---普利策奖得主书的主题，“第六次大灭绝”。

“I am an extinction scientist. In my research I dissect past extinctions to work out what occurred and why. The idea of being able to pin down whether we are in a sixth mass extinction, based on extinction rates measured today, was absolutely astounding to me,” said Hull, who is lead author of the study and an assistant professor of geology and geophysics. “It implied a deep mechanistic and predictive understanding of how mass extinctions unfold that I wasn’t sure we actually had.”

该项研究的带头人并兼地质与地球物理的助教赫尔说，“我是一名研究灭绝的科学家。在研究工作中我分析了过去的灭绝以搞清楚发生过什么以及发生的原因。根据今天估计的灭绝速度，来关注我们是否面临第六次大灭绝，这一想法对我来说绝对是令人震惊的。”“这意味着深刻的机理，仅凭预测来理解大灭绝如何展开，我不确定我们真的理解。”

Hull and her co-authors, Simon Darroch and Douglas Erwin, contend that long before species become extinct, their rarity may cause far-reaching changes in global ecosystems. In fact, the researchers explain, the rarity of previously abundant species and ecosystems alone may be enough to drive permanent shifts in the biosphere. A review of the fossil record, they said, shows that rarity of previously abundant organisms is the only factor tied with certainty to the widespread ecological change observed across extinction boundaries, and because of this, the magnitude and extent of rarity may provide the best comparison of the current biotic crisis to those of the past.

赫尔与她的合著者西蒙.达洛克和道格拉斯.欧文主张很久以前的物种灭绝，其稀缺性可能导致了全球生态系统的深远变化。研究人员解释说，实际上，先前充足物种的稀缺性以及独立的生态系统可能足以推动生物圈的永久性转变。他们说，回顾化石的记录表明先前充足有机体的稀缺性是唯一的因素，它与观测到的跨越灭绝界限的普遍生态变化之必然事件相联系。因此，稀有性的大小和程度可以在当前与过去的生物危机之间提供最好的比较。

“Ecology tells us that ecosystems can collapse completely on timescales ranging from 100 to 10,000 years, which is a process that typically isn’t preserved in the fossil record, so we simply don’t have a good idea of what these transitional ecosystems look like,” Darroch said. “Figuring out how mass rarity in a wide range of species in today’s oceans may scale up to a mass extinction on longer timescales is one of the great scientific challenges of our generation.”

达洛克说，“生态学告诉我们生态系统彻底崩溃的时间范围在100—10000年之间，而这一过程在一般化石的记录中并未保存；因此，这些过度生态系统是怎样的，我们根本无从知晓。”“弄清楚今天海洋中大范围的物种稀有性能如何按比例在更长久的时间表上走向大灭绝，这将是我们这一代人面临的科学大挑战。”

The researchers note, for example, that the modern ocean is full of ecological “ghosts” — species that are now so rare that they no longer fill the ecological roles they did previously, when they were more abundant. In other words, species rarity itself, rather than extinction, can lead to a cascade of changes within ecosystems, long before the species goes extinct, the scientists explain.

例如，研究人员注意到当代海洋里充满了生态的“精灵”，现在稀缺的物种不在像过去丰富的时候那样充当生态的角色了。科学家们解释说，换言之，物种稀缺本身，而不是灭绝，在物种消失之前则能引起生态系统内部的一系列变化。

“The ecological ghosts of oceans past already swim in emptied seas,” the authors said in the paper. But they also noted that today’s fossil record has yet to be written.

“There are steps to take to avoid a mass extinction-like record, even if there are signs of it,” Hull said. “This makes it all the more urgent to act early to protect ecosystems and restore once-abundant species.”

作者们在论文中指出，“过去，海洋的生态精灵已经在空荡的海洋里游荡。”不过，他们还注意到今天的化石记录并未有记载。

赫尔说，“尽管已有一些迹象，也需要采取一些步骤来避免像化石记录那样的大灭绝，”“早期行动保护生态系统并恢复其曾经的丰富物种已是迫在眉睫。”

附：历史上的五次物种大灭绝（来自百度）

第一次物种大灭绝

奥陶纪----海洋无脊椎动物的全盛时期

奥陶纪历经6500万年。第一次物种大灭绝发生在4亿4千万年前的奥陶纪末期。由于当时地球气候变冷和海平面下降，生活在水体的各种不同无脊椎动物变荡然无存。

第二次物种大灭绝

泥盆纪—鱼类的时代

泥盆纪历经约5000万年。第二次物种大灭绝发生在泥盆纪晚期，其原因也是地球气候变冷和海洋退却。

第三次物种大灭绝

二叠纪---生物圈重大变革时期

二叠纪历经4500万年。第三次物种灭绝发生在2.5亿年前的二叠纪末期，毁灭了95%的海洋物种和几乎70%的陆地动物，灾难的主要原因专家仍有争论。

第四次物种大灭绝

三叠纪---裸子植物的兴盛时期

三叠纪历经约5000万年。在三叠纪晚期，发生了第四次物种大灭绝。

第五次物种大灭绝

6千5百万年前---中生代末大灭绝

最为著名的第五次物种大灭绝发生在6千5百万年前。包括恐龙在内的90%的地球物种在这个时期被毁灭。