The threat of invasive species - Jennifer Klos

翻译人员: Zhenning YANG 校对人员: Amy H. Fann

Massive vines that blanket the southern United States,

覆盖美国南部的巨大藤蔓

climbing as high as 100 feet as they uproot trees and swallow buildings.

爬上近百英尺高，并将树木连根拔起，吞没房屋

A ravenous snake that is capable of devouring an alligator.

贪食的蛇可以吞掉鳄鱼

Rabbit populations that eat themselves into starvation.

兔群能将周围的食物吃光

These aren't horror movie concepts.

这不是恐怖电影的情节

They're real stories,

这是真实的故事

but how could such situations exist in nature?

但是这类的情况是如何存在于自然界的呢

All three are examples of invasive species,

接下来举三个物种入侵的实例

organisms harmful not because of what they are,

生物的有害性并不在取决于它们是什么

but where they happen to be.

而取决于它们在哪

The kudzu vine, for example,

比如葛藤

had grown quality in its native east Asia, eaten by various insects

在它的故乡原产地东亚会被各种昆虫食用

and dying off during the cold winters.

而且在寒冬枯萎

But its fortunes changed

但是它时来运转了

when it was imported into the southeastern United States

当它成为门廊装饰和家畜饲料， 并被出口到美国东南部时

for porch decoration and cattle feed.

Its planting was even subsidized by the government to fight soil erosion.

政府为了对抗水土流失甚至鼓励人们种植葛藤

With sunny fields, a mild climate, and no natural predators in its new home,

由于阳光充足、气候温而且没有天敌

the vine grew uncontrollably

在它的新家，葛藤的长势失去控制

until it became known as the plant that ate the South.

直到它被称为“吞食南方的植物”

Meanwhile in Florida's Everglades, Burmese pythons,

与此类似，佛罗里达州的大沼泽地，作为宠物的缅甸巨蟒

thought to have been released by pet owners,

由于被其主人释放到野外

are the cause of decreasing populations of organisms.

导致了该地生物数量的减少

They're successfully outcompeting top predators,

他们成功地战胜了其他顶级捕食者

such as the alligator and panther,

比如鳄鱼和黑豹

causing a significant reduction in their food sources.

导致了它们食物资源的减少

They're not a problem in their native Asia

他们原产地亚洲并不存在这种问题

because diseases, parasites, and predators help to control their population size.

因为疾病、寄生虫和天敌控制了他们的种群规模

And in Australia, European rabbits eat so many plants

在澳大利亚，欧洲野兔食用了大量的植物

that they wipe out the food supply for themselves and other herbivores.

它们吃光了自己和其他本地动物的食物

They're a pretty recent addition,

他们在最近才开始增加

intentionally introduced to the continent because one man enjoyed hunting them.

而他们被人引入这块大陆只是因 有一个人喜欢猎杀它们

Like the Burmese pythons,

像缅甸蟒，

various factors in their native habitat keep their numbers in control.

原产地的多种因素制约了他们的数量

But in Australia, the lack of predators

但是在澳大利亚，天敌的缺失

and a climate perfect for year-long reproduction

和适宜全年繁殖的气候

allows their populations to skyrocket.

使得它们的数量飞涨

So why does this keep happening?

那么，为什么这样的事情经常发生呢？

Most of the world's ecosystems

世界上的大多数生态系统

are the result of millennia of coevolution by organisms,

是由生物经过上千年的共同进化

adapting to their environment and each other

不断的适应彼此和周围环境

until a stable balance is reached.

最终形成的一个稳定的平衡

Healthy ecosystems maintain this balance via limiting factors,

健康的生态系统通过限制因素维持这一平衡

environmental conditions that restrict the size or range of a species.

环境条件限制了物种的大小和范围

These include things like natural geography and climate,

这些条件包括了自然地理、气候

food availability,

食物供应

and the presence or absence of predators.

以及是否存在天敌

For example, plant growth depends on levels of sunlight and soil nutrients.

比如，植物的生长依赖于阳光和土壤营养程度

The amount of edible plants affects the population of herbivores,

可食用植物的规模影响食草动物数量

which in turn impacts the carnivores that feed on them.

这又影响到以它们为食的食肉动物

And a healthy predator population keeps the herbivores from becoming too numerous

一个正常的捕食者数量能够避免食草动物不会过多

and devouring all the plants.

而吃光所有植物

But even minor changes in one factor can upset this balance,

但是，即便某个因素上一个微小的改变都能破坏这一平衡

and the sudden introduction of non-native organisms

并且，突然引进的非本地物种

can be a pretty major change.

可是一个相当大的改变

A species that is evolved in a separate habitat

一个在相对隔绝的栖息地进化的物种

will be susceptible to different limiting factors,

对不同的限制因素

different predators,

不同的捕食者

different energy sources,

不同的能量来源

and different climates.

以及不同的气候都是比较敏感的

If the new habitat's limiting factors fail to restrict the species growth,

如果新栖息地的限制因素不能够限制住物种数量

it will continue to multiply,

那么它将持续增长

out-competing native organisms for resources

与本土生物竞争资源

and disrupting the entire ecosystem.

并且扰乱整个生态系统

Species are sometimes introduced into new habitats through natural factors,

物种偶尔会由于自然因素而将物种引入新栖息地

like storms,

比如，风暴

ocean currents,

洋流

or climate shifts.

或者气候变迁

The majority of invasive species, though, are introduced by humans.

大部分入侵物种由人类引入

Often this happens unintentionally,

通常这是无意间发生的

as when the zebra mussel was accidentally brought to Lake Erie by cargo ships.

就像斑马贻贝被货船意外地带进伊利湖一样

But as people migrate around the world,

但是由于人们在世界范围内迁移

we have also deliberately brought our plants and animals along,

我们通常特意的带上我们的植物或动物一起

rarely considering the consequences.

极少考虑后果

But now that we're learning more

但是现在，我们知道了更多

about the effects of invasive species on ecosystems,

生物入侵对生态环境的影响

many governments closely monitor the transport of plants and animals,

许多政府对动植物运输严密监管

and ban the imports of certain organisms.

并且禁止某些物种入境

But could the species with the most drastic environmental impact

但是，是否当初一群某种灵长类动物 由强烈的环境变化

be a group of primates who emerged from Africa to cover most of the world?

从非洲出发而几乎占领全球呢？

Are we an invasive species?

我们人类到底是不是入侵物种呢？