Dead stuff: The secret ingredient in our food chain - John C. Moore

825,708 views ・ 2014-03-20

TED-Ed


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If someone called you scum,
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you'd probably be offended,
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but scientifically,
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they might not be far off.
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Have you ever thought about
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where your food comes from?
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You might say it comes from
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plants, animals, or even fungi,
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but you'd probably rather not
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think about the rotting organisms and poop
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that feed those plants, animals, and fungi.
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So really, you and most of the matter in your body
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are just two or three degrees of separation
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from things like pond scum.
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All species in an ecosystem,
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from the creatures in a coral reef
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to the fish in a lake
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to the lions on the savannah,
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are directly or indirectly
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nourished by dead stuff.
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Most of the organic matter in our bodies,
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if we trace it back far enough,
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comes from CO2 and water
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through photosynthesis.
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Plants use the energy from sunlight
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to transform carbon dioxide and water from the environment
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into glucose and oxygen.
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That glucose is then transformed
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into more complex organic molecules
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to form leaves, stems, roots, fruit, and so on.
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The energy stored in these organic molecules
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supports the food chains with which we're familiar.
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You've probably seen illustrations like this
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or this.
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These green food chains
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start with living plants at their base.
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But in real-life terrestrial ecosystems,
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less than 10% of plant matter
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is eaten while it's still alive.
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What about the other 90?
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Well, just look at the ground
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on an autumn day.
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Living plants shed dead body parts:
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fallen leaves, broken branches,
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and even underground roots.
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Many plants are lucky enough
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to go their whole lives without being eaten,
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eventually dying and leaving remains.
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All of these uneaten, undigested, and dead plant parts,
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that 90% of terrestrial plant matter?
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That becomes detritus,
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the base of what we call the brown food chain,
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which looks more like this.
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What happens to plants
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also happens to all other organisms up the food chain:
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some are eaten alive,
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but most are eaten only
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when they're dead and rotting.
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And all along this food chain,
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living things shed organic matter
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and expel digestive waste
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before dying and leaving their remains to decay.
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All that death sounds grim, right?
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But it's not.
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All detritus is ultimately consumed
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by microbes and other scavengers,
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so it actually forms the base of the brown food chain
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that supports many other organisms,
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including us.
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Scientists are learning
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that this detritus
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is an unexpectedly huge energy source,
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fueling most natural ecosystems.
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But the interactions within an ecosystem
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are even more complex than that.
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What a food chain really represents
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is a single pathway of energy flow.
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And within any ecosystem,
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many of these flows
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are linked together
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to form a rich network of interactions,
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or food web,
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with dead matter supporting that network at every step.
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The resulting food web
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is so connected
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that almost every species
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is no more than two degrees from detritus,
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even us humans.
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You probably don't eat rotting things,
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poop, or pond scum directly,
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but your food sources probably do.
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Many animals we eat
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either feed directly on detritus themselves,
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like pork, poultry, mushrooms, shellfish,
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or catfish and other bottom feeders,
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or they are fed animal by-products.
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So, if you're thinking nature is full of waste,
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you're right.
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But one organism's garbage is another's gold,
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and all that rotting dead stuff
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ultimately provides the energy that nourishes us
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and most of life on Earth,
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as it passes through the food web.
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Now that's some food for thought.
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