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在新墨西哥州沙漠中對(duì)幾十只蜥蜴的最新研究表明，目前，在全球變暖背景下，用于預(yù)測(cè)物種生存的模型可能偏離了目標(biāo)。

由于地球變暖的速度比這些種群適應(yīng)的速度要快，因此，世界上40%的蜥蜴種群預(yù)計(jì)會(huì)在2080年滅絕。

但是，發(fā)表在美國(guó)國(guó)家科學(xué)院會(huì)議上的最新研究表明，想要做出準(zhǔn)確的預(yù)測(cè)，這些模型必須包括更多的數(shù)據(jù)，遮陽(yáng)地在動(dòng)物的棲息地是如何分布的。

根據(jù)華盛頓大學(xué)生物學(xué)名譽(yù)教授雷蒙德 休伊的介紹，“這是一項(xiàng)突破性的研究”。“研究氣候變暖的科學(xué)家們需要評(píng)估陽(yáng)光和陰涼面積的空間分布，而不能僅僅計(jì)算一個(gè)區(qū)域陽(yáng)光或背陰面積的比例。”

“坦率地說(shuō)，這給我們的研究工作增加了難度，但也更有趣。”

即使體溫發(fā)生很小的變化，也能顯著影響生物體的狀態(tài)。比如，當(dāng)一個(gè)人的體溫上升1到2度。爬行動(dòng)物，包括蜥蜴，通過(guò)在它們棲息地的溫暖和涼爽區(qū)域之間移動(dòng)，來(lái)調(diào)節(jié)自己的體溫。

不僅僅是溫暖和涼爽區(qū)域的相對(duì)比例會(huì)影響蜥蜴如何調(diào)節(jié)它的體溫，休伊說(shuō)，也包括它們?cè)诳臻g上是如何分布的。

在本研究中，如果蜥蜴所處之地有很多小塊的陰涼地，那么它們就能更加有效地調(diào)節(jié)體溫，在這種地形條件下，它們能夠很快爬到陰涼處，如果是一片開(kāi)闊地，有一大片陰涼地，情況就不一樣了。

“取決于環(huán)境的復(fù)雜性，以前估計(jì)的滅絕率或者太高，或者不夠高，”麥克 西爾斯說(shuō)，他是克萊姆森大學(xué)生物學(xué)副教授、該研究的主要作者。

“真正令人擔(dān)心的是，以往的研究低估了滅絕的風(fēng)險(xiǎn)，” 亞利桑那州立大學(xué)教授，研究論文合著者M(jìn)ike Angilletta說(shuō)。

“大多數(shù)模型假設(shè)動(dòng)物在它的環(huán)境中可以在任意時(shí)間抵達(dá)任意地點(diǎn)，卻沒(méi)有考慮動(dòng)物要花費(fèi)多少能量來(lái)調(diào)節(jié)它的體溫。動(dòng)物要移動(dòng)和搜索的陰涼地，當(dāng)陰涼處相距甚遠(yuǎn)時(shí)，它們就很難為自己降溫”Angilletta說(shuō)。

西爾斯花了20年的時(shí)間研究蜥蜴。他說(shuō)爬行動(dòng)物特別適合氣候變化的研究，因?yàn)椤八鼈兿褚苿?dòng)的小小恒溫器。”

休伊說(shuō)，讓這項(xiàng)研究最引人注目的，是它一次解決了三個(gè)問(wèn)題。

“它首次開(kāi)發(fā)了高復(fù)雜性的計(jì)算機(jī)模擬模型，模擬復(fù)雜熱環(huán)境下動(dòng)物的運(yùn)動(dòng)模式，”休伊說(shuō)。“在該研究領(lǐng)域，它加入了大規(guī)模動(dòng)物實(shí)際運(yùn)動(dòng)模式實(shí)驗(yàn)。最后，它顯示出氣候變暖——在現(xiàn)實(shí)熱環(huán)境中——比目前所預(yù)測(cè)的有著更嚴(yán)重的影響。”

當(dāng)西爾斯首次質(zhì)疑目前的模型時(shí)，他建立了一個(gè)計(jì)算機(jī)模擬來(lái)檢驗(yàn)他們的假設(shè)。數(shù)字蜥蜴遵循調(diào)節(jié)體溫最有效的算法。在虛擬環(huán)境中，西爾斯的數(shù)字蜥蜴會(huì)告訴他，當(dāng)陰涼地是聚集在一起或分散開(kāi)的時(shí)候，它們要花費(fèi)多少能量來(lái)調(diào)節(jié)體溫。

在虛擬環(huán)境中，當(dāng)陰涼地是小塊分散的時(shí)候，數(shù)字蜥蜴能夠更加有效地調(diào)節(jié)體溫：它們需要很少的能量就能從一塊陰涼地移動(dòng)到另一塊。在一個(gè)地點(diǎn)，當(dāng)陰涼地是孤立存在的，蜥蜴不得不移動(dòng)到更遠(yuǎn)的地方來(lái)尋找食物，而這需要更多的能量。

西爾斯，Angilletta和來(lái)自另外兩所大學(xué)的同事們，用真蜥蜴驗(yàn)證他們的計(jì)算機(jī)模型，地點(diǎn)是新墨西哥州阿爾伯克基以南80英里，新墨西哥大學(xué)Sevilleta場(chǎng)站附近。

在過(guò)去兩個(gè)夏天，研究人員和他們的學(xué)生在九個(gè)場(chǎng)地設(shè)了圍欄，每一個(gè)場(chǎng)地是20*20平方米。為了模擬仿真的陰涼地，他們?cè)诿恳粋€(gè)場(chǎng)地上用了相同大小的舞臺(tái)遮陽(yáng)布，但是遮陽(yáng)布的分布是不同的，有的是一大片遮陽(yáng)布，4塊陰涼地或16個(gè)小的陰涼地。

在每個(gè)環(huán)境中，每一組蜥蜴呆兩天時(shí)間，研究人員用微型的植入式傳感器對(duì)它們的體溫進(jìn)行監(jiān)測(cè)。

在一大片陰涼地的場(chǎng)地，蜥蜴比四個(gè)陰涼地的場(chǎng)地體溫變化超過(guò)12%，比16個(gè)陰涼地的場(chǎng)地，體溫變化超過(guò)10%。因此，更多的陰涼地意味著能夠更加精細(xì)地調(diào)節(jié)溫度。

這一結(jié)果與西爾斯的計(jì)算機(jī)模型相符。在模擬中，一大片陰涼地與4塊或16塊陰涼地對(duì)比，數(shù)字蜥蜴的體溫變化是9%。

“作為一個(gè)年輕人，我學(xué)到了熱資源的空間分布非常重要，”休伊說(shuō)。“西爾斯和他的同事們將這個(gè)研究課題上升到了新的復(fù)雜水平上，顯示出遮陰地分布如何影響蜥蜴調(diào)節(jié)體溫的能力，以及理解這種分布對(duì)于預(yù)測(cè)氣候變暖的生物反應(yīng)非常關(guān)鍵。”

這項(xiàng)研究證實(shí)了西爾斯的預(yù)感，全球氣溫并不足以預(yù)測(cè)物種的生存。

“如果我們真的想要了解生物種群如何應(yīng)對(duì)氣候變化，我們不能僅僅用一個(gè)簡(jiǎn)單、保守的方法，”西爾斯說(shuō)。“我們需要認(rèn)真思考比現(xiàn)有研究更加精細(xì)的方法。”

“英文原文”

Lizard study finds global warming data not enough to predict animal extinction

Current models used to predict the survival of species in a warming world might be off target, according to new research that enlisted the help of dozens of spiny lizards in the New Mexico desert.

Almost 40 percent of the world's populations of lizards are expected to become extinct by 2080, because the earth is warming faster than these populations can adapt.

But the new study, published in Proceedings of the National Academy of Science, shows that, to make accurate predictions, these models must include much more data about how shade is distributed in an animal's habitat.

"This is a breakthrough paper," according to Raymond Huey, a professor emeritus of biology at the University of Washington. "Scientists studying climate warming will now be forced to evaluate the spatial distribution of sunny-shady patches, and not just compute the fraction of an area that is sunny or shady.

"Frankly, that makes our research lives much harder, but also much more interesting."

Even a small change in body temperature can dramatically affect an organism's well-being, like when a person's temperature rises one or two degrees. Reptiles, including lizards, regulate their body temperatures by moving between warm and cool areas within their home ranges.

It isn't just the relative proportion of warm and cool areas that affects how well a lizard can regulate its temperatures, Huey said, but also how they are distributed in space.

The spiny lizards in the study regulated their temperatures much more efficiently when they had many small patches of shade, which they could easily reach to cool off, instead one large clump of shade in a wide-open space.

"Depending on the complexity of the environment, previous estimates of extinction may be too high or they might not be high enough," said Mike Sears, an associate professor of biology at Clemson University and the lead author of the study.

"The real fear is that previous research has underestimated the risk of extinction," said Mike Angilletta, a professor at Arizona State University and coauthor of the study.

"Most models assume that an animal can be anywhere in its environment at any time, which doesn't account for how much energy an animal spends to regulate its temperature. Animals have to move and search for shade, which makes cooling down more difficult when patches of shade are far apart," Angilletta said.

Sears has spent 20 years studying lizards. He says the reptiles are especially suited for climate change studies because "they're like little thermostats running around."

What makes this study remarkable, Huey said, is that it tackles three issues at once.

"It develops original and highly sophisticated computers simulations of animal movement patterns in complex thermal environments," Huey said. "It adds large-scale experiments of real animal movement patterns in the field. Finally, it shows that climate warming—in realistic thermal landscapes—may have more serious effects than predicted so far."

When Sears first questioned the current models, he built a computer simulation to test their assumptions. Digital lizards followed algorithms that regulated body temperatures most efficiently. In the virtual environment, Sears' digital lizards told him how much energy they spent on regulating their body temperatures when shade was either clumped together or spaced apart.

When shade was dispersed throughout a simulated environment, the digital lizards were able to regulate their temperatures more efficiently: they required less energy to move from patch to patch. When shade was isolated to one location, the lizards had to move farther away to hunt for food, which required more energy.

Sears, Angilletta and colleagues from two other universities tested their computer model with real lizards near the University of New Mexico's Sevilleta Field Station, about 80 miles south of Albuquerque, New Mexico.

Over two summers, the researchers and their students fenced in nine arenas, each 20 by 20 meters square. To mimic the shade of the simulations, they stretched equal areas of shade cloth over each arena, but arranged the cloth differently—one big clump of shade, four medium-sized patches of shade or 16 small patches.

Each group of lizards spent two days in each environment, and their body temperatures were monitored through tiny, surgically implanted sensors.

When the lizards were in the arena with one large clump of shade, their temperatures varied 12 percent more than when they were in the arena with four patches of shade, and 10 percent more than when they were in the arena with 16 patches of shade. Thus, more patches mean more careful thermoregulation.

The results corresponded to Sears' computer model. In the simulations, digital lizards experienced nine percent more variation in body temperature when shade was provided in one clump compared to either four patches or 16 patches.

"As a young lad, I leaned that spatial distribution of thermal resources mattered," Huey said. "But Sears and colleagues take this theme to a general and sophisticated new level, and show how the distribution of shade patches affects the ability of lizards to use behavior to regulate their body temperatures, and also why an understanding of that distribution will be critical to predicting biological responses to climate warming."

The research confirmed Sears' hunch, that global temperatures aren't sufficient for predicting how well species survive.

"If we really want to understand how populations of organisms will respond to climate change, we can't use a simple, back-of-the-envelope method," Sears said. "We need to think on a finer scale than we have been."

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