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气候变化:哪些地球上的物种能逃过劫难

更新时间:2019/9/6 19:12:41 来源:纽约时报中文网 作者:佚名

The animals that will survive climate change
气候变化:哪些地球上的物种能逃过劫难

“I don’t think it will be the humans. I think we’ll go quite early on,” says Julie Gray with a laugh. I’ve just asked Gray, a plant molecular biologist at the University of Sheffield, which species she thinks would be the last ones standing if we don’t take transformative action on climate change. Even with our extraordinary capacity for innovation and adaptability, humans, it turns out, probably won’t be among the survivors.

我询问谢菲尔德大学的植物分子生物学家朱丽·格雷,如果人类不对气候变化危机采取彻底行动,她认为地球上哪些物种将有可能逃脱气候灾难而存活下来。她大笑着回答我,“我认为不会有人类在内。我们人类会一早灭亡。”即使人类有巧夺天工的非凡创造力和适应力,但可能也无法成为幸存者。

This is partly because humans reproduce agonisingly slowly and generally just one or two at a time – as do some other favourite animals, like pandas. Organisms that can produce many offspring quickly may have a better shot at avoiding extinction.

部分原因是人类繁殖后代的速度实在太慢,通常人一生只能养育繁殖一两个后代,类似一些特别受人类青睐的动物,比如熊猫。具备快速生殖大量后代能力的生物逃过灭绝的几率较高。

It may seem like just a thought experiment. But discussing which species are more, or less, able to survive climate change is disturbingly concrete. As a blockbuster biodiversity report stated recently, one in every four species currently faces extinction. Much of this vulnerability is linked to climate change, which is bringing about higher temperatures, sea level rise, more variable conditions and more extreme weather, among other impacts.

这看来只是一个臆想实验。但有关地球各物种逃过气候变化而生存下来几率大小的讨论,却是令人不安的。最近一份引起各方重视的的生物多样性报告声称,目前地球上每四个物种中就有一个面临灭绝之灾。地球生物今天如此之脆弱,很大程度与当今的气候变化有关。气候巨变造成气温升高、海平面上升,而且出现更多极端反常的天气。

Some caveats are in order. While the seriousness of climate change is undeniable, it’s impossible to know exactly how those effects will play out for species vulnerability, especially far into the future. Methods of forecasting vulnerability are ever evolving, while limited and inconsistent data, plus the complex interactions of policies, land-use changes, and ecological effects, mean that projections aren’t set in stone. Climate change vulnerability assessments have had biases and blind spots (just as humans do more generally). Moreover, the indirect effects that are responsible for many climate change impacts on populations, such as in the food chain, are more complex to model than direct effects.

必须发出一些警告。虽然无人否认气候变化会带来严重后果,但也无人能精确认识气候变化将如何影响物种的脆弱性,尤其是在遥远的未来。预测哪些物种难以经受气候变化冲击的方法在不断进展,不过预测获得的数据却很有限,而且有矛盾之处。加上政策、土地使用变更和生态影响之间复杂的交互作用,意味着预测并非很准确,并非不需修改。就像人类通常的行为一样,人类对易受气候变化冲击物种的评估也存在偏见和盲点。此外,还有一些引起不少气候变化的间接因素,也对物种数量产生影响,例如生物食物链方面的影响,这比气候的直接影响更难以建立预测模式。

Another source of uncertainty has to do with life forms’ capacity to adapt. Take ectotherms (cold-blooded animals like reptiles and amphibians), which have historically been slower to adapt to climatic change than endotherms. For one thing, they are less able to adjust their body temperatures. But there are exceptions, like the American bullfrog, which may actually find more habitable environments as a consequence of warming.

另一个不确定性因素与物种的生命适应能力有关。以爬行动物和两栖动物所属的变温动物或冷血动物为例,这些变温动物在演化历史上不如恒温动物那样能很快适应气候的变化。原因之一是,变温动物无法调整自己的体温。不过也有例外,比如美洲牛蛙,可能更适应气候变暖的栖息地。

And, of course, there is an alternative: we humans could get our acts together and stop the climate crisis from continuing to snowball by adopting policies and lifestyles that reduce greenhouse gases. But for the purposes of these projections, we’re assuming that’s not going to happen.

当然,地球物种的命运也有另一种选择,但这要取决于人类。如果我们人类万众一心,采取措施,改变生活方式,减少温室气体的排放,就可以阻止气候危机像滚雪球一样地急速下滑加剧。但我们在预测不同物种受气候暖化冲击的回应和结局时,是假设这没有发生。

Tenacious trends

强不可阻的趋势

Even with the uncertainties, we can make some educated guesses about broad patterns.

即或有上述的不确定性因素,我们也可以对大致的模式做出一些有根据的猜测。

Heat tolerant and drought resistant plants, like those found in deserts rather than rainforests, are more likely to survive. So are plants whose seeds can be dispersed over long distances, for instance by wind or ocean currents (like coconuts), rather than by ants (like some acacias). Plants that can adjust their flowering times may also be better able to deal with higher temperatures. Jen Lau, a biologist at Indiana University Bloomington, suggests that this may give non-native plants the advantage when it comes to responding to climate change.

耐高温耐干旱的植物,比如生长在沙漠而不是雨林中的植物,存活的可能性就会比较高。存活率较高的还有种子可以远距离传播的植物,比如靠风或洋流传播种子,如椰子,而靠蚂蚁传播种子的相思树就不会那么幸运。此外,能够调整开花周期的植物也能更好地应对气温的升高。印第安纳大学布鲁明顿分校的生物学家Jen Lau认为,这可能会让非原生地的植物具有适应气候变化的优势。

We also can look to history as a guide. The fossil record contains signs of how species have coped with previous climatic shifts. There are genetic clues to long-term survival too, such as in the hardy green microalgae that adapted to saltier environments over millions of years – a finding only made in September 2018 by Fatima Foflonker of Rutgers and colleagues.

我们也可以在地质史中找寻向导。生物化石藏有物种如何应对地球以前气候变化的踪迹。化石中也能找到生存历时久远的遗传线索,比如改变自身去适应盐度更高的环境而生存了数百万年的耐寒绿色微藻。这是美国新泽西罗格斯大学的科学家法蒂玛‧佛隆格(Fatima Foflonker)和她的同事刚在2018年9月的新发现。

Importantly, though, the uniquely devastating nature of the current human-made climate crisis means that we can’t fully rely on benchmarks from the past.

然则,重要的是,当前人类造成的气候危机独有的毁灭性,意味着我们不能完全依照远古地质时代物种的气候适应变化为基准。

“The climate change that we see in the future will differ in many ways from the climate change that we’ve seen in the past”, notes Jamie Carr, an outreach officer for the Climate Change Specialist Group of the IUCN Species Survival Commission.

国际自然保护联盟(IUCN)物种存续委员会气候变化专家小组的外联官员吉米‧卡尔(Jamie Carr)指出:"我们在未来看到的气候变化将在很多方面都有别于过去的气候变化。"

The historical record does point to the tenacity of cockroaches. These largely unloved critters “have survived every mass extinction event in history so far”, says Asmeret Asefaw Berhe, a soil biogeochemist at the University of California, Merced. For instance, cockroaches adapted to an increasingly arid Australia, tens of millions of years ago, by starting to burrow into soil.

化石确切记录了蟑螂生命适应力之坚韧顽强。加州大学默塞德分校的土壤生物地球化学家艾斯莫雷提‧贝赫(Asmeret Asefaw Berhe)说,这种很不受人喜爱的小动物"经历了地球史上每一次物种灭绝事件都存活了下来"。例如,蟑螂在数千万年前开始向土壤深处挖洞来适应日益干旱的澳大利亚大地。

This shows two characteristics, says Robert Nasi, the director general of the Center for International Forestry Research (CIFOR): an “ability to hide and protect in buffered conditions (e.g. underground)” and a long evolutionary history, as in general “ancient species appear more resilient than younger ones”. These are among the traits that, Nasi says, are linked to surviving large catastrophic events which triggered major changes in climate.

国际林业研究中心(CIFOR)主任罗伯特‧纳西(Robert Nasi)说,蟑螂显示了物种适应变化的两个特性,一是"善于找到缓冲环境,如地下,而自我隐藏和保护的能力",二是其漫长的进化史,因为一般来说,"古老物种似乎比年轻物种更有适者生存的能力"。纳西说,这类特性使得这类物种能够熬过引发气候巨变的大型灾难性事件而继续生存下来。

Cockroaches also tend to not be picky eaters. Having broad diets means that climate change will be less of a threat to the food sources of species that are not too fussy about their food, such as rats, opportunistic birds, and urban raccoons.

此外蟑螂也不挑食。什么东西都可以用来饱腹。这意味,对食物不太挑剔的物种,如老鼠、机会主义的鸟类和适应人类城市生活的浣熊,气候变化对它们的食物源威胁不大。

As a comparison, take an animal like the koala. Koalas eat primarily eucalyptus leaves, which are becoming less nutritious due to increasing CO2 levels in the atmosphere. As a result, climate change is increasing their risk of starvation.

相比之下,挑食的动物就难以适应气候的变化。比如澳大利亚的树熊,或曰无尾熊,仅以桉树叶为食。但由于大气中二氧化碳含量的增加,桉树叶所含的营养也越来越少。结果,气候变化增加了树熊挨饿的风险。

As well as having a specialised diet, koalas have low genetic diversity – one reason that chlamydia has ravaged wild koala populations. These are worrying traits in terms of extinction risk. “In many cases, specialised species are those that we expect to see disappear first,” says Carr. This extends to species in microhabitats like high elevation montane forests, or those in narrow ranges, like some tropical birds or small-island plants. Also vulnerable are species that depend on pristine environments.

澳洲树熊除了食物的单一化,其遗传多样性也很低,这也是致病微生物衣原体为何能蹂躏野生树熊的原因之一。这些都是令人担忧的可导致物种灭绝的特性。卡尔说:“在很多个案中,我们特别关注的物种是那些我们预料会首先消失的物种。”这些脆弱物种包括生活在微小生态中的物种,如高海拔山地森林,或栖息在狭小区域的生物,如一些热带鸟类或仅出现在某些小岛的植物。依赖原始环境的物种也很易受到气候变化而绝种。

That’s compared to the “early successional” species that succeed in disturbed habitats, such as grasslands and young forest. These species “might do well under climate change because they thrive in states of change and transition”, says Jessica Hellmann, who leads the Institute on the Environment at the University of Minnesota. “For example, deer (in the US) are common in suburban areas and thrive where forests have been removed or are regularly disturbed.”

这可用来与在生态受破坏的栖息地,如草原和新生林等地,能成功生长繁育的“早期演替”物种做比较。明尼苏达大学 (University of Minnesota) 的环境研究所所长杰茜卡•赫尔曼 (Jessica Hellmann )说,这些早期演替物种"在气候变化中可能适应较好,因为这类物种就是在环境变化和过度的状态下茁壮生长。比如在美国,经常在城市郊外出没的鹿,在森林被砍伐或经常受到破坏的地方鹿也能繁衍后代。"

Species that Carr calls “mobile generalists”, which can move and adapt to different environments, are likely to be more durable in the face of climate change. While this adaptability is generally positive, it might come at a cost to other parts of an ecosystem. Invasive species like cane toads, which are poisonous, have led to local extinctions of other species like quolls (carnivorous marsupials) and monitors (large lizards) in Australia. And Hellmann says that the versatility of invasive plant species “leads to the worry that, in addition to losing vulnerable species, a warmer world will be a weedier world”. The weeds typically found along roadsides may be especially long-lasting in comparison with other plants.

卡尔称之为"移动的多能者"之物种,能够迁徙和适应于不同的生态环境,因此遭遇气候变化时其存续的时期也会较长。虽然这类物种的适应性通常是正面的,但也可能让一个生态系统的其他部分付出代价。像美洲巨蟾蜍这种有毒的物种入侵澳大利亚,导致了澳大利亚一些原生物种的灭绝,比如一种食肉有袋动物袋鼬和一种大型蜥蜴。赫尔曼说,入侵植物的本事是多样性,这"不由得让人担心,气候暖化不仅会让一些脆弱的物种消失,还会让这个世界只有杂草才能繁茂生长"。在路边小道上常见的杂草,野火烧不尽,春分吹又生,生命力远远超过其他植物。

Of course, many organisms are intrinsically less mobile. Most plants will be unable to move quickly enough to keep pace with rapid heating, although they’ve done so in response to the slower climatic changes of the past.

当然,许多生物体本质就不具迁徙性或迁徙性甚低。地球上大多数植物虽然已能适应过去比较缓慢的气候变化,但将无法跟上气候的急剧暖化步伐而做出快速的回应。

Buffer zones

缓冲区

The good news is that some specialised species might have a buffer known as climate change refugia: areas that are relatively protected from climate change’s consequences, such as deep sea canyons. Although deep sea zones are heating up and declining in oxygen concentrations, Jonathon Stillman, a marine environmental physiologist at San Francisco State University, suggests that deep sea hydrothermal vent ecosystems, specifically, might be one bright spot in an otherwise mostly bleak situation.

利好的消息是,一些特殊物种可能拥有称之为气候变化避难所的缓冲区,即相对而言不受气候变化影响的地区,比如深海海谷。尽管深海区域的海水升温,氧气浓度下降,但旧金山州立大学的海洋环境生理学家乔纳森‧斯蒂尔曼 (Jonathon Stillman)认为,深海热泉生态系统在基本上是一片黑暗无光的世界中可能是一个亮点。

“They are pretty much uncoupled from the surface of our planet and I doubt that climate change will impact them in the least,” he says. “Humanity didn’t even know they existed until 1977. Their energy comes from the core of our Earth rather than from the Sun, and their already extreme habitat is unlikely to be altered by changes happening at the ocean surface.”

他说,这个深海中的生态系统“与地球表面几乎没有关联,我怀疑气候变化会对它们有任何影响。人类是到了1977年,才知道海洋深处有这样的生态系统存在。深海热泉生态系的能量来自地球的核心,而不是太阳,因此其本来就极端的生命栖息地不太可能被海洋表面的生态变化所影响。”

Similarly, Douglas Sheil, a tropical forest ecologist at the Norwegian University of Life Sciences, suggests that “at some point in the future the only vertebrate species surviving in Africa might be a blind cave fish deep underground”. As in the deep sea hydrothermal vents, “many species remain undiscovered and thus unknown – Europe’s first cave fish was only found in Germany in 2015.”

挪威生命科学大学热带森林生态学家道格拉斯•希尔 (Douglas Sheil) 也提到类似的独立于地表生态系统而免受气候变化所影响的物种。他说,“在未来的某个时候,非洲唯一能幸存的脊椎动物有可能是生活在地底深处的盲穴鱼”。与深海热泉系统一样,生活在地底洞穴的“许多物种仍未被人发现,自然也不为人所知。欧洲的第一条洞穴鱼直到2015年才在德国被发现。”

Thermophiles (heat-adapted organisms) living in extreme environments like volcanic springs are also likely to be less affected by surface temperature changes. Indeed, the organisms best able to live in severe circumstances are microbes, as noted by many of the scientists I’ve surveyed. Computer modelling suggests that only microbes would be able to survive increasing solar intensity. Soil biogeochemist Berhe says of archaea, one of the major types of microbes, “these critters have figured out how to live in the most extreme of environments”.

生活在火山热泉等极端环境中的嗜热生物,或曰耐热有机体,也可能较少受到地表温度变化的影响。正如我访问过的许多科学家所言,最能适应恶劣环境而生存的生物是微生物。电脑模拟说明,只有微生物才能承受不断增加的太阳热力而生存下来。土壤生物地球化学家比尔赫(Berhe)提到一种主要的微生物类型古生菌,说"这类微生物已经学会如何在最极端的环境中生存"。

Not quite as tiny but also nearly indestructible are tardigrades, commonly known as water bears. Environmental physiologist Stillman enthuses: “They can survive the vacuum of outer space, extreme dehydration, and very high temperatures. If you are a Star Trek fan, you have learned about them in a sci-fi setting, but they are real creatures that live across most habitats on Earth.”

虽然细小,但也并非微细如微生物,也一样大难临头不会死的是一种俗称为水熊虫的缓步动物。环境生理学家斯蒂尔曼(Stillman)兴奋说道,这种小动物"能在外太空的真空状态,以及极度脱水和高温下存活。如果你是《星际迷航》(Star Trek)的粉丝,你应该会在片子的科幻场景中见识到这一物种,但它们不是科幻,是生活在地球上大多数栖息地的真实生物。"

The future will have not only more extreme environments, but also more urban, human-altered spaces. So “resistant species would likely be the ones that are well attuned to living in human-modified habitats such as urban parks and gardens, agricultural areas, farms, tree plantations, and so on”, says Arvin C Diesmos, a herpetology curator at the Philippine National Museum of Natural History.

未来的地球不仅会有更多的极端自然环境,而且会有更多的城市和人为改造的空间。因此,菲律宾国家自然历史博物馆的爬虫学展厅的总管阿尔文·迪莫斯 (Arvin C Diesmos)说,“能抗极端环境的物种很可能是这样的物种,能安居于人类改造过的栖息地,比如城市公园和花园、农业地区、农场、人工林等等。”

CIFOR’s Nasi sums it up. “The winners will be very small, preferably endotherms if vertebrates, highly adaptable, omnivorous or able to live in extreme conditions.”

国际林业研究中心的纳西作了这样的总结,“如果脊椎动物适应力强,能够杂食,或能在极端条件下生存,其中的赢家将是非常小的动物,希望是恒温动物。”

In the words of the IUCN’s Carr, “It doesn’t sound like a very pretty world.”

用国际自然保护联盟的卡尔的话来说,“这样的地球听起来不像是一个美丽多彩的世界。”

Of course, to some extent we already know what’s needed to limit the bleakness of the future natural world. This includes reducing greenhouse gases; protecting biodiversity; restoring connectivity between habitats (rather than building endless dams, roads and walls); and reducing interrelated threats like pollution and land harvesting. Even species that are close to extinction, like Saiga antelopes, can be brought back from the brink with enough conservation effort. To reflect the power of sustained conservation, scientists are developing a Green List of species on the road to recovery and full health, to complement the IUCN’s Red List of threatened species.

当然,人类已经或多或少知道需要有什么样的行动来减缓未来自然世界的黯淡前景。这些行动包括减少温室气体排放,保护生物多样性,恢复各栖息地之间的连通性,停止无止境地建造水坝、道路和围墙,减少污染和土地开采等会伤及其他领域的生态破坏。只要人类能尽到环境保育的责任,即使是濒临灭绝的物种,比如大鼻羚羊,也能从灭绝的边缘被挽救回来。为了向世人宣示生态可持续保护的力量,科学家们正在制定一份正在起死回生恢复全面健康的物种绿色名单,以补充国际自然保护联盟的濒危物种红色名单。

The political barriers are daunting. But scaling them, it seems, would beat surrendering the planet to the microbes.

阻难行动的政治障碍望之令人生畏。但是,在地球将会被拱手让给微生物之际,看来只要我们能排除掉这些障碍,就能力挽狂澜,救回我们的地球。

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