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

爬上近百英尺高 將樹木連根拔起且吞沒房屋

A ravenous snake that is capable of devouring an alligator.

極餓的蛇可以吞掉鱷魚

Rabbit populations that eat themselves into starvation.

兔群能將周圍的食物吃光

These aren't horror movie concepts.

這不是恐怖電影的情節

They're real stories,

這是真實的故事

but how could such situations exist in nature?

但為甚麼會發生這些事件?

All three are examples of invasive species,

上面三個物種入侵的實例

organisms harmful not because of what they are,

生物危害並不取決於它們是什麼

but where they happen to be.

而取決於它們在哪

The kudzu vine, for example,

比如葛藤

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

在原產地東亞它被各種昆蟲食用

and dying off during the cold winters.

而且在寒冬枯萎

But its fortunes changed

但是它時來運轉了

when it was imported into the southeastern United States

它被當作門廊裝飾和飼料

for porch decoration and cattle feed.

出口到美國東南部

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

政府為解決水土流失 甚至鼓勵種植葛藤

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

由於陽光充足、 氣候溫和而且沒有天敵

the vine grew uncontrollably

在它的新家，葛藤的生長失去控制

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

直到它被稱為“吞食南方的植物”

Meanwhile in Florida's Everglades, Burmese pythons,

佛羅里達州的大沼澤地也一樣

thought to have been released by pet owners,

作為寵物的緬甸巨蟒

are the cause of decreasing populations of organisms.

被主人野放 導致該地生物量的減少

They're successfully outcompeting top predators,

他們成功地戰勝了 其他頂級捕食者

such as the alligator and panther,

比如鱷魚和黑豹

causing a significant reduction in their food sources.

導致了該地生物數量的減少

They're not a problem in their native Asia

他們原產地亞洲並沒有這種問題

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

因為有疾病、寄生蟲 和天敵控制了族群規模

And in Australia, European rabbits eat so many plants

在澳大利亞， 歐洲野兔食用大量的植物

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

它們吃光自己 和其他本地動物的食物

They're a pretty recent addition,

他們在最近才開始增加

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

他們被引進只因 有人喜歡獵殺牠們

Like the Burmese pythons,

像緬甸蟒

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

原產地的自然因素 控制了他們的數量

But in Australia, the lack of predators

但是在澳大利亞沒有天敵

and a climate perfect for year-long reproduction

和適宜全年繁殖的氣候

allows their populations to skyrocket.

使得它們的數量暴增

So why does this keep happening?

為什麼這樣的事情經常發生呢？

Most of the world's ecosystems

世界上的大多數生態系統

are the result of millennia of coevolution by organisms,

是由生物經過上千年的共同進化

adapting to their environment and each other

不斷的適應周圍環境

until a stable balance is reached.

最終形成的一個穩定的平衡

Healthy ecosystems maintain this balance via limiting factors,

健康的生態透過 自然因素維持平衡

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

環境條件限制了 物種的大小和範圍

These include things like natural geography and climate,

這些條件包括了自然地理、氣候

food availability,

食物供應

and the presence or absence of predators.

以及是否存在天敵

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

比如植物的生長 依賴陽光和土壤養分

The amount of edible plants affects the population of herbivores,

可食用植物的規模 影響草食動物數量

which in turn impacts the carnivores that feed on them.

這又影響到 以它們為食的肉食動物

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

健全的掠食族群能 避免草食動物過多

and devouring all the plants.

而吃光所有植物

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

但即使是微小的改變 都能破壞平衡

and the sudden introduction of non-native organisms

像是突然引進非本地物種

can be a pretty major change.

可能會帶來相當大的改變

A species that is evolved in a separate habitat

一個在相對隔絕的 棲息地進化的物種

will be susceptible to different limiting factors,

對不同的限制因素

different predators,

不同的掠食者

different energy sources,

不同的能量來源

and different climates.

以及不同的氣候都是比較敏感的

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

如果新棲息地的限制因素 不能夠限制住物種數量

it will continue to multiply,

那麼它將持續增長

out-competing native organisms for resources

與本土生物競爭資源

and disrupting the entire ecosystem.

並且擾亂整個生態系統

Species are sometimes introduced into new habitats through natural factors,

物種偶爾會因自然因素而引入新棲息地

like storms,

比如風暴

ocean currents,

洋流

or climate shifts.

或者氣候變遷

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

大部分入侵物種由人類引入

Often this happens unintentionally,

通常這是無意間發生的

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

就像斑馬貽貝 被貨船意外地帶進伊利湖一樣

But as people migrate around the world,

但是由於人們在世界範圍內遷移

we have also deliberately brought our plants and animals along,

我們通常刻意攜帶 我們的植物或動物同行

rarely considering the consequences.

極少考慮後果

But now that we're learning more

但是現在我們知道更多

about the effects of invasive species on ecosystems,

對於生物入侵對生態環境的影響

many governments closely monitor the transport of plants and animals,

許多政府對動植物運輸嚴密監管

and ban the imports of certain organisms.

並且禁止某些物種入境

But could the species with the most drastic environmental impact

但是當初有一群靈長類動物 由於強烈的環境變化

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

從非洲出發且幾乎佔領全球呢？

Are we an invasive species?

我們人類到底是不是入侵物種呢？