If someone called you scum, you'd probably be offended, but scientifically, they might not be far off. Have you ever thought about where your food comes from? You might say it comes from plants, animals, or even fungi, but you'd probably rather not think about the rotting organisms and poop that feed those plants, animals, and fungi. So really, you and most of the matter in your body are just two or three degrees of separation from things like pond scum. All species in an ecosystem, from the creatures in a coral reef to the fish in a lake to the lions on the savannah, are directly or indirectly nourished by dead stuff. Most of the organic matter in our bodies, if we trace it back far enough, comes from CO2 and water through photosynthesis. Plants use the energy from sunlight to transform carbon dioxide and water from the environment into glucose and oxygen. That glucose is then transformed into more complex organic molecules to form leaves, stems, roots, fruit, and so on. The energy stored in these organic molecules supports the food chains with which we're familiar. You've probably seen illustrations like this or this. These green food chains start with living plants at their base. But in real-life terrestrial ecosystems, less than 10% of plant matter is eaten while it's still alive. What about the other 90? Well, just look at the ground on an autumn day. Living plants shed dead body parts: fallen leaves, broken branches, and even underground roots. Many plants are lucky enough to go their whole lives without being eaten, eventually dying and leaving remains. All of these uneaten, undigested, and dead plant parts, that 90% of terrestrial plant matter? That becomes detritus, the base of what we call the brown food chain, which looks more like this. What happens to plants also happens to all other organisms up the food chain: some are eaten alive, but most are eaten only when they're dead and rotting. And all along this food chain, living things shed organic matter and expel digestive waste before dying and leaving their remains to decay. All that death sounds grim, right? But it's not. All detritus is ultimately consumed by microbes and other scavengers, so it actually forms the base of the brown food chain that supports many other organisms, including us. Scientists are learning that this detritus is an unexpectedly huge energy source, fueling most natural ecosystems. But the interactions within an ecosystem are even more complex than that. What a food chain really represents is a single pathway of energy flow. And within any ecosystem, many of these flows are linked together to form a rich network of interactions, or food web, with dead matter supporting that network at every step. The resulting food web is so connected that almost every species is no more than two degrees from detritus, even us humans. You probably don't eat rotting things, poop, or pond scum directly, but your food sources probably do. Many animals we eat either feed directly on detritus themselves, like pork, poultry, mushrooms, shellfish, or catfish and other bottom feeders, or they are fed animal by-products. So, if you're thinking nature is full of waste, you're right. But one organism's garbage is another's gold, and all that rotting dead stuff ultimately provides the energy that nourishes us and most of life on Earth, as it passes through the food web. Now that's some food for thought.
如果有人叫你废物, 你或许会觉得他冒犯了你。 但从科学角度来看, 他们可能没完全说错。 你可否想过 你每天吃的食物从何而来? 你或许会说这些食物来自 植物、动物、或者真菌类植物, 但你可能不愿想到, 腐烂的有机物和粪便 是植物、动物和真菌类植物的食物。 所以事实上, 你以及你的身体的大多数物质 同池塘中的淤泥 也不过是两三个食物链级的分别。 生态系统内的所有物种, 从珊瑚礁里的生物 到湖里的鱼, 再到大草原的狮子, 都直接或间接地 由死去的东西喂养。 我们身体内大多数有机物质, 如果我们追根究底, 都来自由光合作用产生的 二氧化碳和水。 植物用来自光照的能量 将环境中的二氧化碳和水 转化为葡萄糖和氧气。 葡萄糖又转换为 结构更加复杂的有机分子, 成为叶、茎、根、果实等形成的基础。 这些储存在有机分子中的能量 维持着我们所熟悉的食物链的运转。 你或许见过与此相似的图表, 或者这个。 这些绿色食物链 以活体植物作为它们的基础。 但在现实的陆地生态系统中, 不到10%的植物体 在它们依然活着的时候被吃掉。 那么剩下的90%去哪了呢? 好吧,那我们就在某个秋天 低头看看地上。 活着的植物枯萎死去的部分会掉落: 败叶、枯枝, 甚至是地下的根茎。 很多植物足够幸运能够度过 整个生命周期而不被吃掉, 最终死去,尸体保留了下来。 那所有那些没有被吃掉,被消化 并且已经死去的植物部分, 我们前面所提到的90%的陆地植物呢? 它们变成了腐质, 是我们称之为“棕色食物链” (腐食食物链)的基础, 看起来更像这个。 发生在植物上的一切, 也同样发生在食物链上端的 其他所有生物身上: 有些在活着的时候就被吃了, 但大多数 在死掉腐烂之后才被吃掉。 并且沿着整个食物链, 有机物质会从活体上脱落, 活体在死之前排出可分解的废弃物 并留下它们的遗体,直至腐烂。 所有这些死亡听起来很残酷,是吧? 但事实并非如此。 所有腐质最终会 被微生物及其他食腐动物吃光, 所以说,腐质事实上是 形成“棕色食物链”的基础, 支撑了许多其他生物的生存, 包括我们。 科学研究发现, 出人意料的是, 这些腐质是巨大的能量来源, 为大多数自然生态系统提供燃料。 但一个生态系统内的相互作用 要比这个复杂的多。 一条食物链真正代表的 是一个单独的能量流动的途径。 并且,在任一生态系统中, 许多像这样的流动途径 彼此交错连结, 形成一个强大的相互联系的网络, 或称食物网, 死了的东西支撑了这个网络的 每一个环节。 由于食物网各个环节 如此紧密相连, 以至于食物网中几乎每个物种 同腐质的联系都不超过两个消费级, 甚至我们人类也包括在内。 你或许不直接吃腐烂的东西, 如粪便或者塘泥, 但你所吃的食物或许是以这些为生。 很多我们所吃的动物, 要么是直接由腐质喂养的, 比如说猪肉、家禽、蘑菇、贝类, 或者鲶鱼及其他底层动物; 要么就是以动物的副产品为生。 所以说, 如果你认为大自然充满了废物, 你算是说对了。 但你认为是垃圾的东西 别人可能认为是金子, 并且所有这些腐烂的死了的东西, 随着在食物网中的层层传递, 最终提供了喂养我们及地球上 大多数生命所需的能量。 这的确是让人回味无穷的事实。