k********k
发帖数: 5617 | 1 http://news.yahoo.com/disappearance-wildflowers-may-doomed-ice-
冰河時期北極野花消失 可能導致了巨獸滅絕
Disappearance of wildflowers may have doomed Ice Age giants
By Will Dunham2 hours ago
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By Will Dunham
WASHINGTON (Reuters) - Flower power may have meant the difference between
life and death for some of the extinct giants of the Ice Age, including the
mighty woolly mammoth and woolly rhinoceros.
Scientists who studied DNA preserved in Arctic permafrost sediments and in
the remains of such ancient animals have concluded that these Ice Age beasts
relied heavily on the protein-rich wildflowers that once blanketed the
region.
But dramatic Ice Age climate change caused a huge decline in these plants,
leaving the Arctic covered instead in grasses and shrubs that lacked the
same nutritional value and could not sustain the big herbivorous mammals,
the scientists reported in the journal Nature on Wednesday.
The change in vegetation began roughly 25,000 years ago and ended about 10,
000 years ago - a time when many of the big animals slipped into extinction,
the researchers said.
Scientists for years have been trying to figure out what caused this mass
extinction, when two-thirds of all the large-bodied mammals in the Northern
Hemisphere died out.
"Now we have, from my perspective at least, a very credible explanation,"
Eske Willerslev of the University of Copenhagen, an expert in ancient DNA
who led an international team of researchers, said in a telephone interview.
The findings contradicted the notion that humans arriving in these regions
during the Ice Age caused the mass extinction by hunting the big animals
into oblivion - the so-called overkill or Blitzkrieg hypothesis.
"We think that the major driver (of the mass extinction) is not the humans,"
Willerslev said, although he did not rule out that human hunters may have
delivered the coup de grace to some species already diminished by the
dwindling food supplies.
The Arctic region once teemed with herds of big animals, in some ways
resembling an African savanna. Large plant eaters included woolly mammoths,
woolly rhinos, horses, bison, reindeer and camels, with predators including
hyenas, saber-toothed cats, lions and huge short-faced bears.
The scientists carried out a 50,000-year history of the vegetation across
the Arctic in Siberia and North America.
They obtained 242 permafrost sediment samples from various Arctic sites and
studied the feces and stomach contents from the mummified remains of Ice Age
animals recovered in places like Siberia. They determined the age of the
samples and analyzed the
DNA.
While many scientists had thought the ecosystem had been grasslands and the
big animals were grass eaters, this study showed it instead was dominated by
a kind of plant known as forbs - essentially wildflowers.
"The whole Arctic ecosystem looked extremely different from today. You can
imagine these enormous steppes with no trees, no shrubs, but dominated by
these small flowering plants," Willerslev said.
Christian Brochmann, a botanist at the Natural History Museum at the
University of Oslo, said the permafrost contained "a vast, frozen DNA
archive left as footprints from past ecosystems," that could be deciphered
by exploring animal and plant collections already stored in museums.
(Reporting by Will Dunham, editing by G Crosse) | k********k
发帖数: 5617 | 2 冰河時期北極野花消失, 而不是人類過分狩獵，可能導致了猛犸象等巨獸滅絕. | c*********r
发帖数: 19468 | 3 为了发文章而发的文章……最多说明或许野花是一个因素，但是是不是决定性的因素？
拿美洲来说，一万多年前开始灭绝的巨兽不计其数，光是大象至少就有7种，分布范围
从北美冰原到南美，其中有grazer也有browser，怎么可能是野花这么一个因素就能解
释的？而且如果没有人类的影响，野花的变化是个足够漫长的过程，这些动物应该有足
够的机会来适应，在第四纪冰期里植被变化都N个轮回，难道野花的分布会不受影响？
这些都没有造成这些巨兽灭绝呢……
【在 k********k 的大作中提到】
: 冰河時期北極野花消失, 而不是人類過分狩獵，可能導致了猛犸象等巨獸滅絕.
| h*h
发帖数: 18873 | 4 觉得人类开始用投枪，投石器，弓箭，是这些巨兽消失的重要原因
【在 c*********r 的大作中提到】
: 为了发文章而发的文章……最多说明或许野花是一个因素，但是是不是决定性的因素？
: 拿美洲来说，一万多年前开始灭绝的巨兽不计其数，光是大象至少就有7种，分布范围
: 从北美冰原到南美，其中有grazer也有browser，怎么可能是野花这么一个因素就能解
: 释的？而且如果没有人类的影响，野花的变化是个足够漫长的过程，这些动物应该有足
: 够的机会来适应，在第四纪冰期里植被变化都N个轮回，难道野花的分布会不受影响？
: 这些都没有造成这些巨兽灭绝呢……
| c*********r
发帖数: 19468 | 5 嗯，从全球范围讲，这是唯一说得通的解释。自然环境的变化的确会在某些时期把某种
巨兽的数量降到很低的程度，但如果没有人类的新的因素，它们或许会有大得多的几率
活到它们适应新环境或者环境变会有利于它们的情形，但是人类的出现很容易就能把处
于瓶颈期数量及其有限的巨兽们彻底灭门了（捕猎以及对自然环境进一步的改造）。近
代这种事情又不是没发生过，马达加斯加的象鸟、古大狐猴，毛里求斯的渡渡鸟，新西
兰的恐鸟、哈斯特鹰，白令海的大海牛，塔斯马尼亚的袋狼……例子不要太多哦……
【在 h*h 的大作中提到】
: 觉得人类开始用投枪，投石器，弓箭，是这些巨兽消失的重要原因
| Z*****o
发帖数: 4090 | |
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