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

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When you picture the lowest levels of the food chain, you might imagine herbivores happily munching on lush, living green plants. But this idyllic image leaves out a huge (and slightly less appetizing) source of nourishment: dead stuff. John C. Moore details the "brown food chain," explaining how such unlikely delicacies as pond scum and animal poop contribute enormous amounts of energy to our ecosystems.

Lesson by John C. Moore, animation by TED-Ed.

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.