Ecosystem Ecology

History of Earth

Hank Green 

(Source: http://open.163.com)

 Ecosystem ecology

There's a lot of ideas that we just assume we know a lot about

because we hear about them all the time.

For instance, I know what Pop music is

but if you were to corner me at a party

and say,"HANK, What is Pop Music?",

I'd be like, "It's uh... it's like, uh...

the music that plays on the pop station?"

Just because we're familiar with a concept does 

mean that we actually understand it

Ecology's kind of the same way: even though it's a common,

everyday concept, and ecosystem is a word that we hear a lot

I think most of us would be little stumped if somebody

actually asked us what an ecosystem is or how one works,

or why they're important, etc.

I find it helps to think of an ecosystem, a collection of living

and nonliving things interacting in a specific place,

as one of those Magic Eye posters, for those of you who were

sentient back in 1994 .

An ecosystem is just a jumble of or ganisms, weather patterns,

geology and other stuff that don't make a lot of sense together

until you stare at them long enough, from far enough away,

and then suddenly a picture emerges.

And just like with Magic Eye posters, it helps if you're

listening to Jamiroquai  while you're doing it.

So, the discipline of ecosystem ecology, just like other

types of ecology we've been exploring lately, looks at a

particular level of biological interaction on Earth.

But unlike population ecology, which looks at interactions

between individuals of one species,

or community ecology,

which looks at how bunches of living things interact with each other,

ecosystem ecology looks at how energy

and materials come into an ecosystem, move around in it,

and then get spat back out.

In the end, ecosystem ecology is mostly about eating

who's eating whom, and how energy, nutrients and other

materials are getting shuffled around within the system.

So today, we're setting the record straight!

No more not understanding how an ecosystem works! Starting NOW!

So, ecosystems may be a lot like Magic Eye posters,

but the way that they're not like a Magic Eye poster is

in the way that posters have edges.

 

Ecosystems... I'll just come out and say it: No edge.

Only fuzzy, ill-defined gradients that bleed

into the ecosystems next door.

So actually defining an ecosystem can be kind of hard.

Mostly it depends on what you want to study.

Say you're looking at a stream in the mountains.

This stream gets very little sunlight because it's so small

that the trees on its banks totally cover it with shade.

As a result, very few plants or algae live in it, and if there's one

thing that we know about planet Earth it's that plants are king.

Without plants, there are no animals.

But somehow there's a whole community of animals living in and

around this mountain stream, eventhough there are few plants in it.

So what are the animals doing there,

and how are they making their living?

From the land, of course! From the ecosystems around it.

Because no stream is an island. It isn't there all by itself.

All kinds of food, nutrientsand other materials drop into

the stream from the trees or are washed into it when it rains,

leaves and bugs, you name it, flow down from

neighboring terrestrial ecosystems.

And that stuff gets eaten by bigger bugs, which get eaten by fish,

which in turn are eaten by raccoons and birds and bears.

So, even though the stream's got its own thing going on, without

the rest of the watershed, the animals there wouldn't survive.

And without the stream, plants would be thirsty and

terrestrial animals wouldn't have as many fish to eat.

So where does the ecosystem of the stream start

and where does it end?

This is a perennial problem for ecologists.

Because the way it works, energy and nutrients are imported

in from someplace, they're absorbed by the residents of

an ecosystem, and then passed around within it for a little while,

and then finally passed out, sometimes into another ecosystem.

This is most obvious in aquatic systems, where little streams

eventually join bigger and bigger waterways until they finally reach

the ocean, this flow is afundamental property of ecosystems.

So, at the end of the day, how you define an ecosystem just

depends on what you want to know.

If you want to know how energy and materials come in,

move through, and are pooped out of a knot in a tree that

has a very specific community of insects and protists living in 

you can call that an ecosystem.

 

 

If you want to know how energy and materials are introduced to,

used and expelled by the North Pacific Gyre,

you can call that an ecosystem.

If you want to know how energy and materials move around a

cardboard box that has a rabbit and a piece of lettuce in it,

you can call that an ecosystem.

I might tell you that your ecosystem is stupid,

but go ahead! Do whatever you want!

The picture you see in an ecosystem's Magic Eye is actually

dictated by the organisms that live there

and how they use what comes into it.

An ecosystem can be measured through figuring out things

like its biomass, that is,

the total weight of living things in the ecosystem,

and its productivity, how much stuff is produced,

and how quickly stuff grows back,

how good the ecosystemis at retaining stuff.

And of course, all these parameters matter to neighboring

ecosystems as well because if one ecosystem's really productive,

the ones next door are going to benefit.

So first things first, where do the energy and materials come from?

And to be clear, whenI talk about "materials,"

I'm talking about water or nutrients like phosphorous or nitrogen,

or even toxins like mercury or DDT.

Let's start out by talking about energy,

because nothing lives without energy,

and where organisms get  their energy tells the story of an ecosystem.

You remember physics, right?

The laws of conservation state that energy and matter

can neither be destroyed or created.

They can only get transferred from place to place to place.

The same is true of an ecosystem.

Organisms in an ecosystem

organize themselves into a trophic structure,

with each organism situating  itself in a certain place in the food chain.

All of the energy in an ecosystem moves around within

this structure, because when I say energy, of course I mean food.

For most ecosystems, the primary source of energy is the sun,

and the organisms that do most of the conversion of

solar energy into chemicalenergy... you know this one.

Who rules the world? The plants rule the world.

Autotrophs like plants are able to gather up the sun's energy,

and through photosynthesis, make something awesome out of it:

little stored packets of chemical energy.

So whether it's plants, bacteria or protists that use photosynthesis,

autotrophs are always the lynchpin of every ecosystem,

the foundation upon which all other organisms

in the system get their energy and nutrients.

For this reason, ecologists refer to plants as primary producers.

Now, obviously, the way that energy gets transferred

from plants to animals is by an animal eating the plant.

For this reason, herbivores are known as primary consumers,

the first heterotrophs to get their grubby paws

on that sweet, sweet energy.

After this stage in the trophic structure, the only way

to wrestle the solar energy that was in the plants

that the herbivore ate is to, you guessed it, eat the herbivore,

which carnivores, known as secondary consumers, are very happy to do.

And assuming that the ecosystem is big enough

and productive enough,

there might even be a higher level of carnivore

that eats other carnivores, like an owl that eats hawks,

and these guys are called tertiary consumers.

And then there are the -vores that decompose all the dead animal

and plant matter, as well as the animal poop: detritivores.

These include earthworms, sea stars, fiddler crabs, dung beetles,

fungi, and anything else that eats the stuff that

none of the rest of us would touch with a 3 -meter pole.

So, that's a nice, hierarchical look at who's getting energy

from what or whom within an ecosystem.

But of course, organisms within an ecosystem don't usually

abide by these rules very closely, which is why these days,

we usually talk about food webs, rather than food chains.

A food web takes into consideration that sometimes a fungus

is going to be eating nutrients from a dead squirrel,

and other times squirrels are going to be eating the fungi.

Sometimes a bear likes to munch on primary producers,

blueberry bushes, and other times it's going to be snacking

on a secondary consumer, like a salmon.

And even the tippy tippy top, predators get eaten by stuff

like bacteria in the end, which might or might not be the same

bacteria that ate the top predator's poopies.

Circle of Life!

It's also worth noting that the size and scope of the food web

in an ecosystem has a lot to do with things like water

because water and temperature are

what plants like, right?

And without plants, there isn't going to be

a whole lot of trophic action going on.

Take, for example, the Sonoran desert,

which we've talked about before.

There aren't very many plants there,

compared to, say, the Amazon rainforest.

So the primary producers are limited by the lack of water,

which means that primaryconsumers are limited by lack

of primary producers, and that leaves precious few secondary

consumers, a few snakes, some coyotes and hawks.

All this adds up to the Sonoran not being a terribly productive

place, compared to the Amazon at least, so you might

only get to the level of tertiary consumer occasionally.

Now, all this conversation about productivity leads me

to another point about ecosystem efficiency.

When I talk about energy getting passed along from one place

to another within an ecosystem, I mean that in a general sense,

organisms are sustaining each other,

but not in a particularly efficient way.

In fact, when energy transfers from one place to another,

from a plant to a bunny or from a bunny to a snake,

the vast majority of that energy is lost along the way.

So, let's take a cricket.

That cricket has about 1 calorie of energy in it.

And in order to get that 1 calorie of energy it had

to eat about 10 calories of lettuce.

Where did the other 9 calories go? It is not turned into cricket flesh.

Most of it is used just to live, like to power its muscles,

or run the sodium potassium pumps in its neurons, it's just used up.

So only the 1 calorie of the original 10 calories of food

is left over asactual cricket stuff.

And then, right after his last meal, the cricket jumps into

a spider web and is eaten by a spider,

who converts only 10% of the cricket's energy

into actual spider stuff.

And don't get me started on the bird that eats the spider.

This is not an efficient world that we live in.

But you want to know what's scary-efficient?

The accumulation of toxins in an ecosystem.

Elements like mercury, which are puffed out the smokestacks

of coal-fired power plants, end upgetting absorbed in the ocean

by green algae and marine plants.

While the tiny animal that eats the algae only stores 10%

of the energy it got, it keeps 100% of the mercury.

So as we move up the chain, each trophic level consumes

ten times more mercury than the last,

and that's what we call bioaccumulation.

Concentrations get much higher at each trophic level,

until a human gets a hold of a giant tuna that's at the top

of the marine food chain, and none of that mercury has been lost.

It's all right there in that delicious tuna flesh.

Because organisms only hold on to 10% of the energy they ingest, each

trophic level has to eat about 10 times its biomass to sustain itself.

And because 100 % of the mercury moves up the food chain,

that means that it becomes 10 times more concentrated

with each trophic level it enters.

That's why we need to take the seafood advisories seriously:

as somebody who could eat anything you wanted,

it's probably safest to eat lower on the food chain,

primary producers or primary consumers.

The older, bigger, higher in the food chain,

the more toxic it's going to be.

And that's not just my opinion, that's ecosystem ecology!

Thank you for watching this episode of Crash Course Ecology.