Feedback loops: How nature gets its rhythms - Anje-Margriet Neutel

回饋循環：自然的旋律 — 努安瑪 (Anje-Margriet Neutel)

譯者: Aaron Shoo 審譯者: Regina Chu

試音、試音，1、2、3...

Testing, testing, one, two, three.

When your band is trying to perform, feedback is an annoying obstacle,

樂團表演的時候， 「回饋」是很麻煩的阻礙。

但在大自然的交響樂中， 回饋不只有益，

but in the grand orchestra of nature, feedback is not only beneficial,

it's what makes everything work.

更是不可或缺的一部份。

What exactly is feedback?

所以「回饋」到底是什麼？

The key element, whether in sound, the environment or social science,

無論在是聲音、環境、 或社會科學的領域，

is a phenomenon called mutual causal interaction,

「回饋」的主要形式 就是「互為因果」。

X 影響 Y， Y 再回過頭影響 X 等等。

where x affects y, y affects x, and so on,

會創造出不斷循環的「回饋循環」。

creating an ongoing process called a feedback loop.

And the natural world is full of these mechanisms

大自然裡充斥著這種機制，

formed by the links between living and nonliving things

藉由生物和非生物間的互動，

維持族群數量

that build resilience by governing the way populations

and food webs respond to events.

和食物網的穩定消長。

When plants die, the dead material enriches the soil with humus,

植物枯萎後， 會變成「腐植質」滋養土壤，

a stable mass of organic matter, providing moisture and nutrients

「腐植質」是一種穩定的有機物，

提供水分和養分讓其他植物生長。

for other plants to grow.

越多植物生長和枯萎，

The more plants grow and die, the more humus is produced,

就製造出越多腐植質。

allowing even more plants to grow, and so on.

又會讓更多植物得以生長。

This is an example of positive feedback,

這就是「正回饋」的例子，

an essential force in the buildup of ecosystems.

是讓生態系發展的重要推手。

But it's not called positive feedback because it's beneficial.

會叫「正回饋」 不是因為有「正面」效果，

Rather, it is positive because it amplifies a particular effect or change

而是因為過程中 會「正向」放大影響或改變。

from previous conditions.

These positive, or amplifying, loops can also be harmful,

這種正向或說放大的循環， 也可能有害。

like when removing a forest makes it vulnerable to erosion,

就像我們砍伐森林 容易造成水土流失，

which removes organic matter and nutrients from the earth,

水土流失會把有機質和營養帶走，

leaving less plants to anchor the soil, and leading to more erosion.

植物因此更難生長， 水土流失就更嚴重。

In contrast, negative feedback diminishes or counteracts changes in an ecosystem

相反地，「負回饋」會消彌 或制衡生態系的改變，

to maintain a more stable balance.

以維持穩定的平衡。

Consider predators and their prey.

比如說獵食者和獵物。

When lynx eat snowshoe hares, they reduce their population,

山貓捕食雪兔， 雪兔的因此數量減少。

but this drop in the lynx's food source will soon cause their own population to decline,

食物來源減少的情況下， 山貓的數量也跟著下降。

reducing the predation rate and allowing the hare population to increase again.

天敵減少讓雪兔的數量重新增長。

The ongoing cycle creates an up and down wavelike pattern,

這樣不斷的循環， 會創造出此消彼長的波狀起伏，

maintaining a long-term equilibrium and allowing a food chain to persist over time.

維持長期的均衡和食物鏈的穩定。

Feedback processes might seem counterintuitive because many of us

回饋機制聽起來拐彎抹角，

因為我們很習慣直觀、 可預期的因果關係。

are used to more predictable linear scenarios of cause and effect.

For instance, it seems simple enough that

舉一個簡單的例子來說，

spraying pesticides would help plants grow by killing pest insects,

農藥會殺死害蟲讓作物長得好，

但搞不好會帶來 其他意想不到的影響。

but it may trigger a host of other unexpected reactions.

For example, if spraying pushes down the insect population,

因為若農藥把蟲殺死，

its predators will have less food.

牠的天敵就沒有食物；

As their population dips,

天敵數量若因此減少，

the reduced predation would allow the insect population to rise,

蟲子的數量會因為 沒有掠食者又上升，

counteracting the effects of our pesticides.

所以農藥等於沒用。

Note that each feedback is the product of the links in the loop.

每一個回饋都是 廣大迴圈的一部份。

Add one negative link and it will reverse the feedback force entirely,

加入一個負回饋， 迴圈結果可能完全相反；

and one weak link will reduce the effect of the entire feedback considerably.

某個回饋效果變弱， 也會造成最後產出的改變；

Lose a link, and the whole loop is broken.

若回饋斷了， 整個循環可能就崩解了。

但這只是簡單的例子，

But this is only a simple example,

since natural communities consist not of separate food chains,

因為大自然不是由 不相干的食物鏈，

but networks of interactions.

而是互賴的食物網構成。

Feedback loops will often be indirect, occurring through longer chains.

回饋循環仰賴複雜的網路運作。

一個包含 20 個物種的食物網， 可以有 1000 條循環，

A food web containing twenty populations can generate thousands of loops

of up to twenty links in length.

每條由20個以上的回饋相繫。

But instead of forming a disordered cacophany,

但生態系中的回饋循環，

不會造成混亂的雜音，

feedback loops in ecological systems play together,

而是像數種樂器一起

creating regular patterns just like multiple instruments,

調和出規律、和諧又豐富的樂章。

coming together to create a complex but harmonious piece of music.

Wide-ranging negative feedbacks keep the positive feedbacks in check,

正回饋會受負回饋的廣泛制衡，

like drums maintaining a rhythm.

就像鼓聲穩定節奏。

You can look at the way a particular ecosystem functions within its unique habitat

你可以想像成每個生態系

依照棲地分類， 有不同的代表旋律。

as representing its trademark sound.

海洋生態系以獵捕關係為主，

Ocean environments dominated by predator-prey interactions,

and strong negative and positive loops stabilized by self-damping feedback,

負回饋強烈， 加上穩定抑制的正回饋，

are powerful and loud, with many oscillations.

聽起來大聲、有能量 而且起伏大。

Desert ecosystems, where the turn over of biomass is slow,

沙漠生態系的「生物質」累積慢，

and the weak feedbacks loops through dead matter are more like a constant drone.

能量的回饋循環也慢， 就像持續不斷的重低音。

And the tropical rainforest, with its great diversity of species,

雨林生態系充滿多樣性物種，

high nutrient turnover, and strong feedbacks among both living and dead matter,

生物質累積快， 生命間的能量循環強，

is like a lush panoply of sounds.

所以聽起來熱鬧華麗。

Despite their stabilizing effects,

雖然有所謂的穩定機制，

many of these habitats and their ecosystems develop and change over time,

棲地和生態系還是可能 隨時間發展產生改變，

這些旋律也是。

as do the harmonies they create.

Deforestation may turn lush tropics into a barren patch,

濫墾濫伐可能會讓 華麗的熱帶樂曲變得了無生趣，

like a successful ensemble breaking up after losing its star performers.

就像成員各自單飛以後的過氣樂團。

But an abandoned patch of farmland may also become a forest over time,

但是被遺棄的農田 有一天也可能變回森林，

like a garage band growing into a magnificent orchestra.

就像三流樂隊 漸漸蛻變成頂尖樂團。