So...

in your book in Chapter 17

the importance of wolves to the 
Yellowstone ecosystem

is the main topic.

And we have talked already about 
the connections between living things

and their environment;

and how there are different

types of interactions.

We also found out that wolves fulfill

a very important role in the community:

they're a keystone species.

Which means that they have a really

big influence for their population size 
on the community structure;

and their presence or absence can really 
change that community structure.

Wolves occupy

a very important niche in the 
Yellowstone ecosystem.

And a niche simply refers to,

what is an organisms role in 
its environment?

What does it do?

Who does it interact with, and how?

What are its needs?

So, really, the needs and the...

interactions of an organism

in an ecosystem

describe this concept of a niche.

Basically, everything about how

it acts in that ecosystem.

If there is overlap of a niche,

a place where needs and roles overlap,

then we get our last type of biological 
interaction: competition.

Competition is going to take place

when two organisms,

two species,

or two members of the same species

are interacting in a way that indicates 
that they are competing for a resource.

So, for example, here we have a 
little parakeet

and a starling that are fighting 
over a french fry.

Now, hypothetically...

in the case of competition,

one competitor will usually manage to 
exclude the other competitor for that

--from that resource--

and we refer to this as 
competitive exclusion.

Organisms can compete for lots of things.

They can compete for space,

like these corals.

Um...

the corals are also competing 
for sunlight.

There is some algae sort of growing
here in the corner of the picture;

and as that algae grows over the coral 
it takes up the sunlight and the coral

can't get it.

So organisms can compete for physical 
resources like:

space, sunlight, nutrients,
water, things like that.

Organisms can compete for food.

The lions and hyenas are competing 
for food here.

You saw some competition in the 
"Battle At Krueger" video.

There was some very interesting
competitive interactions taking place.

Organisms can compete for mates.

These are two male elephant seals,

uh, who are competing to become 
the "beach master."

And that is a real term that describes the
male elephant seal that has control of

all the females on the beach.

Elephant seals have a harem mating system

where one male mates with the females,
and, of course,

for that evolutionary fitness, for that
reproductive success,

that is a very hotly contested position.

You can see they are battling pretty hard.
They are bloody and fighting, uhm...

What's really interesting about the 
elephant seal situation is that you do

have a little bit of disruptive selection.

There are "sneaker males," as well,
in that system.

But, there is very intense competition 
for mates.

When organisms compete

they can compete in different ways.

Some organisms compete by taking up, 
using up a resource.

And we refer to this as exploitation 
competition.

Now, this is different from the 
exploitation that we talked about earlier

when we talked about how parasites 
and predators exploit other organisms.

In the case of exploitation competition, 
you can also think of it as "scramble."

This squirrel is hoarding nuts.

He's gathered up nuts and he is sitting
on them and he's com--com--com...

um, taking up that resource and 
keeping other organisms from getting it.

So exploitation competition can happen
when an organism uses up a resource

and doesn't allow other organisms to 
access it.

Interference competition, 
on the other hand,

is when you have organisms that are 
physically competing, or interfering,

with one another for a resource.

This is sometimes referred to as 
"contest competition."

So, in this case you have a, uh...

a little ground squirrel and some 
starlings that are competing for nuts.

And, instead of--instead of the ground 
squirrel hogging all the nuts

and just setting them aside,

instead what we have is an actual, 
physical altercation,

a fight if you will, for that resource.

So, exploitation competition: 
using up the resources.

Interference competition: physically 
competing over them and--and

physically keeping other organisms from
having them.

So those are two different strategies 
for competition.

And depending on the organism and 
the resource, you might see either

of those take place.

The coral example here, we have the 
algae is engaging

in exploitation competition by

covering up the coral and keeping it 
from getting light.

The elephant seals are engaging in 
interference competition

by physically battling one another

for the mates.

Okay...

When competition occurs

one of the things that we see

is that one competitor,

if they have the same exact needs,

will often out compete the other 
predator.

So here are two protists.

Um , Paramecium aurelia and
Paramecium caudatum.

That, if grown in separate flasks,

in separate conditions,

we see almost the exact same 
population growth curves.

They grow in the same way.

If, however, we put them in the same flask

Paramecium aurelia ultimately out competes
Paramecium caudatum

because two organisms cannot occupy
the same niche simultaneously

and continuously.

This is known as competitive exclusion.

So, the parrot and the starling competing 
for a french fry,

if they lived in the exact same 
environment and only ate the same

food, over time what we would see 
is one competitor would be a superior

competitor; out compete the other one.
and we would get competitive exclusion.

How organisms get around this is through 
resource partitioning.

For example:

this is a group of birds, warblers,

a closely related species,

that are engaging in 
resource partitioning.

They use different resources

to allow them

to effectively coexist.

So, some of the warblers use 
different parts of the tree.

The myrtle warbler, for example, is found
in the mid-section, the lower mid-section

of the tree.

While the cape may warbler is found
at the tops of the trees.

They eat different things.

Black throated warblers that live sort of 
near the tops are eating

small worms and grubs.

Where cape may warblers are actually
uh, eating flying insects.

So we have different forms of competition

different types of resources being
used here.

Different spaces, different food items...

And so these birds have engaged
in resource partitioning

where they take advantage of 
different resources

so that they can still gain a foothold 
in the ecosystem.

One of the things we might see 
here though is that

some areas of this tree, or some types of 
insect prey may not be as desire--

as desirable as others.

So that when one resource is 
removed, or one competitor is removed

we might see changes.

And so competition really can 
influence distributions in time and space.

Here is an example from the 
Oregon Coast.

We have two different species that are 
living on the coastline here,

we have barnacles

and we have mussels.

And these two organisms both like to 
live in the inner tidal zone.

This is an area between the high and low 
tides that is partially covered by water

during a portion of the day .

And mussels tend to be very quickly 
growing.

They grow fast, they are a little 
bit bigger, and they can actually

-and you see this happening here-

they can crush and squeeze out barnacles.

They are engaging in some exploitation 
competition where they are physically

taking up a resource and keeping other 
organisms from getting it.

The problem that mussels have

is that...

while they are competitively excluding 
these barnacles

they are limited to the area

that is covered by water for much 
of the day.

They have a much lower tolerance 
for drying out than the barnacles do.

And so we see this very distinct,

what's called a zonation line,

that's separating the mussels and the 
barnacles

because barnacles can live in those
higher, inner tidals

where there is less wave splash, 
but mussels can't survive.

So this is a good example of resource 
partitioning.

The mussels have excluded the barnacles
from the--the wet zone down here

but he barnacles, because they can last
a little bit longer out of water,

have been able to engage in resource 
partitioning and use this space up

in the high inner tidal.

What's kind of exciting

is that if mussels are removed in some way

then barnacles will spread

to fill the available space.

So perhaps we have a sea star predator 
that comes up here,

removes and eats the mussels,

barnacles will then spread to fill 
that available space

and this is known as 
"competitive release."

Basically if a superior competitor 
is removed

then the other competitor may take 
advantage of that better resource.

They don't have to resource partition 
anymore.

And so this the reason that sea stars
are, themselves, considered a keystone

species on the Oregon Coast

and throughout the Pacific Northwest

because they wipe out big mussel 
populations and allow other kinds of

organisms to live in the inner tidal.

So, competition has a really big 
influence here,

but if our sea star comes along and 
removes that superior competitor,

it changes the community--

making the sea star another example
of a keystone species.

And you can see that here in this 
actual picture of the, um, these sea stars

that come up to a certain level of the 
inner tidal

they've eaten a whole bunch 
of these mussels.

Remember from our example of
co-evolution,

sea stars are great at eating shellfish
because they pry open that shell

just a little bit

and push their stomachs inside out and
inside that shell and--and dissolve those

nutrients in there and then
[clicks tongue]

pull their stomachs back into their 
bodies.

So, here they have created this 
line of mussels and if you look below

the mussel line you can see all these
different kinds of seaweed,

there's some other shells downs here,

some barnacles.

And they have really changed the 
community.

And we have different populations 
taking part in that community.

We have mussels,

we have sea stars,

we have barnacles,

we have algae,

all of those populations,

all the members of a species that are 
living together in a place

are interacting...

in this community.

And what we are going to see

is that competition

can occur between members of a 
community.

Like a lion and a crocodile.

And, in this case, what are a lion and 
a crocodile gonna compete for?

Well, they're certainly competing for 
food.

But, they may not be competing for 
all of the same things.

So here we have niche overlap that is 
just partial .

In this case, the lion and the crocodile

they're not competing for the same 
place to live;

the crocodile prefers an aquatic 
environment, the lion does not.

They're certainly not competing for mates.

However...

lions are going to have 100% niche overlap
with other members of the same species.

And so competition tends to be much 
more intense between members

of the same species.

That's the difference between 
interspecific competition:

competition that takes place between 
members of a different species

and intraspecific competition that takes
place between members of the same species.

And the real difference here is 
complete niche overlap.

If you're in the same species

you're competing for food,

for living space,

for mates,

because you have the exact same needs.

So one of the things that we see with 
competition that's really interesting

is that intraspecific competition tends to
be the most intense competition

and is going to be much more intense,

in many cases,

than interspecific competition.

We are going to be focusing more next
week on other kinds of dynamics that

influence the shape,

and size of these pop...

We are going to be looking in much 
more detail next week at other kinds

of interactions that influence the shape
and size of these populations.

In the meantime, don't forget to do the 
"Battle At Krueger" online exercise for

your 5 activity points
and to also participate in the discussion

forum for this week where you can ask
and answer questions.

I will also be asking and 
answering questions

and that is going to help us 
keep up on these community interactions.