Testing, testing, one, two, three.
测试，测试，1，2，3。
When your band is trying to perform, feedback is an annoying obstacle,
当你的乐队准备登台演出时，反馈噪音是一个很烦人的问题，
but in the grand orchestra of nature, feedback is not only beneficial, it's what makes everything work.
但是在自然界，这个世界上最大规模的交响乐演出中，反馈不仅仅是有益的，更是让一切事物有序运转的关键。
What exactly is feedback? The key element, whether in sound, the environment or social science,
那么到底什么是反馈呢？无论是在声音、环境科学或者是社会科学中，
is a phenomenon called mutual causal interaction, where x affects y, y affects x, and so on,
最关键的要素是一种叫做相互因果关系的现象，也就是x先影响y，y再影响x，等等，
creating an ongoing process called a feedback loop.
产生一种叫做反馈回路的持续过程。
And the natural world is full of these mechanisms formed by the links between living and nonliving things
在自然界中这样的机制随处可见，通过生物及非生物之间的链接，
that build resilience by governing the way populations and food webs respond to events.
利用种群数量和食物网的自然规律来打造自然适应力。
When plants die, the dead material enriches the soil with humus,
当植物死亡后，死植给土壤提供腐殖质，
a stable mass of organic matter, providing moisture and nutrients for other plants to grow.
腐殖质是一种为其他植物的生长提供所需的水分及营养的稳定的有机物质。
The more plants grow and die, the more humus is produced, allowing even more plants to grow, and so on.
植物死亡的越多，土壤中的腐殖质就越多，土壤就会更加肥沃，生长更多的植物，如此往复。
This is an example of positive feedback, an essential force in the buildup of ecosystems.
这就是一个正反馈的例子，一个生态环境中非常重要的组成部分。
But it's not called positive feedback because it's beneficial.
但我们并不是因为其有益而称其为正反馈。
Rather, it is positive because it amplifies a particular effect or change from previous conditions.
而是因为这种反馈作用将之前的改变扩大了影响。
These positive, or amplifying, loops can also be harmful,
这种正向的，或者说放大的循环也可能有害，
like when removing a forest makes it vulnerable to erosion, which removes organic matter and nutrients from the earth,
比如当我们砍伐森林，导致水土流失，也就同时去除了土壤中的养分和有机物，
leaving less plants to anchor the soil, and leading to more erosion.
这样植物就会死亡，从而导致更多的腐殖质产生。
In contrast, negative feedback diminishes or counteracts changes in an ecosystem to maintain a more stable balance.
相反，负向反馈通过减弱或阻碍生态系统中的改变来达到一个更加稳定的平衡。
Consider predators and their prey.
想想捕食者和它们的猎物：
When lynx eat snowshoe hares, they reduce their population,
当山猫捕食野兔时，野兔的数量会减少，
but this drop in the lynx's food source will soon cause their own population to decline,
但是野兔数量的减少会很快导致山猫食物的缺乏，最终导致山猫数量同样减少，
reducing the predation rate and allowing the hare population to increase again.
山猫的种群数量下降导致了野兔的天敌变少，从而使得野兔的种群数量又回升。
The ongoing cycle creates an up and down wavelike pattern,
这种往复的循环形成上下波浪状的模式
maintaining a long-term equilibrium and allowing a food chain to persist over time.
达到了一个长期的均衡，且使得食物链稳定。

Feedback processes might seem counterintuitive
反馈的过程可能对于大多数人来说是违反直觉的，
because many of us are used to more predictable linear scenarios of cause and effect.
因为我们大都习惯了可预测性的、线性关系的因果关系。
For instance, it seems simple enough that spraying pesticides would help plants grow by killing pest insects,
举个例子来说，众所周知，喷洒杀虫剂能杀灭害虫帮助植物生长，
but it may trigger a host of other unexpected reactions.
但是这个过程可能会导致一系列出乎意料的后果。
For example, if spraying pushes down the insect population, its predators will have less food.
比如说，如果喷药使得昆虫数量降低，捕食昆虫的动物就会面临食物缺乏。
As their population dips, the reduced predation would allow the insect population to rise,
它们的种群数量就会降低，而此就会导致昆虫的数量回升，
counteracting the effects of our pesticides.
抵消了我们喷洒杀虫剂的效果。
Note that each feedback is the product of the links in the loop.
请注意，每一个反馈都是这个循环弧中的一个因素。
Add one negative link and it will reverse the feedback force entirely,
加入一个负向的因素就会改变整个循环的方向，
and one weak link will reduce the effect of the entire feedback considerably.
加入一个弱的因素会大大减弱整个反馈的能力。
Lose a link, and the whole loop is broken.
缺少一个因素，整个循环会崩溃。
But this is only a simple example, since natural communities consist not of separate food chains, but networks of interactions.
但这只是一个简单的例子，因为自然界中没有独立的食物链，而是一个互相影响的巨大网络。
Feedback loops will often be indirect, occurring through longer chains.
反馈循环经常是间接的，并且发生在一个较长的食物链中。
A food web containing twenty populations can generate thousands of loops of up to twenty links in length.
一个包含着20个种群的食物网会产生上千种不同的循环，每个循环都会有20个环节。
But instead of forming a disordered cacophany,
但是相对于混乱如麻的关系，
feedback loops in ecological systems play together, creating regular patterns
生态系统中的反馈回路一起创造出了一个共有的篇章，
just like multiple instruments, coming together to create a complex but harmonious piece of music.
就像许多种乐器一起演奏出一首悦耳的奏鸣曲。
Wide-ranging negative feedbacks keep the positive feedbacks in check, like drums maintaining a rhythm.
大范围的负向反馈使得正向反馈不会太过强大，就像鼓声保持着节奏。
You can look at the way a particular ecosystem functions within its unique habitat as representing its trademark sound.
你可以看到一个生态系统用他自己独特的方式维持着自己的正常运行。
Ocean environments dominated by predator-prey interactions,
海洋环境被捕食与被捕食的关系所主宰，
and strong negative and positive loops stabilized by self-damping feedback, are powerful and loud, with many oscillations.
正负向反馈被自减震反馈作用相抵消，但是过程中充斥着震耳欲聋的振动声。
Desert ecosystems, where the turn over of biomass is slow,
在缓慢的沙漠生态系统中，
and the weak feedbacks loops through dead matter are more like a constant drone.
通过死亡物质发生作用的微弱反馈就更像是持续的嗡鸣声。
And the tropical rainforest, with its great diversity of species,
在极具多样性的热带雨林中，极高的营养交换率，
high nutrient turnover, and strong feedbacks among both living and dead matter, is like a lush panoply of sounds.
生物及死亡物质作用的强反馈就像首复杂而和谐的交响乐。
Despite their stabilizing effects,
由于他们的稳定作用，
many of these habitats and their ecosystems develop and change over time, as do the harmonies they create.
许多栖息地和他们的生态系统不断的发展和改变，同时它们也非常和谐的共存着。
Deforestation may turn lush tropics into a barren patch,
沙漠化进程可能会将一片富饶的热带雨林变成贫瘠的荒地，
like a successful ensemble breaking up after losing its star performers.
就像一个乐队组合在失去了他们的明星后解散。
But an abandoned patch of farmland may also become a forest over time,
但一片被遗忘的农田也有可能变成一片广袤的森林，
like a garage band growing into a magnificent orchestra.
就像一个车库乐队最终变成了一个伟大的交响乐团。