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.
Kada bi vas neko nazvao smećem, verovatno biste se uvredili, ali s naučne tačke gledišta, oni ne bi puno pogrešili. Da li ste ikada razmišljali o tome odakle potiče naša hrana? Možda ćete reći da potiče od biljaka, životinja, ili čak gljiva, ali o njoj radije ne biste mislili kao o organizmima koji trunu i izmetu kojim se hrane te biljke, životinje i gljive. Zapravo, vi i većina materije u vašem telu ste zapravo odvojeni dva ili tri stepena od stvari poput otpada iz bare. Sve vrste u jednom ekosistemu, od stvorenja na koralnom grebenu do riba u jezeru i lavova u savani, direktno ili indirektno zavise od mrtvih stvari. Većina organske materije u našim telima, ako je ispratimo dovoljno daleko, dolazi iz CO2 i vode kroz fotosintezu. Biljke koriste energiju iz sunčeve svetlosti da pretvore ugljen-dioksid i vodu iz okoline u glukozu i kiseonik. Glukoza se onda pretvara u kompleksnije organske molekule kako bi stvorila lišće, stabljike, korenje, plodove i ostalo. Energija koja se skladišti u ovim organskim molekulima održava lance ishrane koji su nam poznati. Verovatno ste videli ilustracije poput ove ili ove. Ovi zeleni lanci ishrane u osnovi počinju sa živim biljkama. Ali u pravim zemaljskim ekosistemima, manje od 10% materija iz biljaka se jede dok su one još žive. Šta je sa drugih 90? Pa, samo pogledajte u tlo na jesenjem danu. Žive biljke odbacuju mrtve delove tela: opalo lišće, slomljene grane, čak i podzemno korenje. Mnoge biljke su dovoljno srećne da prođu ceo život a da ih neko ne pojede, na kraju uginu i od njih ostanu ostaci. Svi ovi nepojedeni, nesvareni i mrtvi delovi biljke, tih 90% zemaljske biljne materije? To postaje nanos, osnova onoga što zovemo smeđim lancem ishrane, što izgleda kao ovo. Ono što se dešava sa biljkama, dešava se i sa drugim organizmima u lancima ishrane - neki se jedu dok su živi, ali većina se jede samo kada su mrtvi i truli. Uz sav ovaj lanac ishrane, živa bića odbacuju organsku materiju i izbacuju otpad iz digestivnog trakta pre nego što uginu i njihovi ostaci se raspadnu. Sva ta smrt zvuči prilično tmurno, zar ne? Ali nije. Sam nanos na kraju konzumiraju mikrobi i drugi lešinari, tako da on zapravo čini osnovu smeđeg lanca ishrane koja izdržava mnoge organizme, uključujući i nas. Naučnici saznavaju da je ovaj nanos neočekivano velik izvor energije, i snabdeva većinu prirodnih ekosistema. Ali interakcije unutar ekosistema su kompleksnije i od toga. Lanac zapravo predstavlja jedinstvenu putanju toka energije. Unutar bilo kog ekosistema, mnogi od ovih tokova su povezani kako bi sačinili bogatu mrežu interakcija ili mrežu hrane, gde mrtva materija izdržava tu mrežu tokom celog procesa. Mreža hrane koja nastane je tako povezana da je skoro svaka vrsta na ne više od dva stepena od nanosa, čak i mi ljudi. Verovatno ne jedete stvari koje trunu, izmet ili direktan otpad iz bare, ali izvori vaše hrane to verovatno rade. Mnoge životinje koje jedemo se ili direktno same hrane nanosom, poput svinjetine, živine, gljiva i ostriga ili somova i drugih članova dna lanca ishrane, ili ih hrane životinjskim nusproduktima. Tako da, ako mislite da je priroda puna otpada, u pravu ste. Ali smeće za jedan organizam je zlato za drugi, a sve te mrtve stvari koje trunu na kraju pružaju energiju koja održava nas i većinu života na Zemlji, dok prolazi kroz mrežu hrane. Eto nečega za razmišljanje.