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So...

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in your book in Chapter 17

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the importance of wolves to the 
Yellowstone ecosystem

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is the main topic.

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And we have talked already about 
the connections between living things

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and their environment;

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and how there are different

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types of interactions.

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We also found out that wolves fulfill

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a very important role in the community:

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they're a keystone species.

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Which means that they have a really

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big influence for their population size 
on the community structure;

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

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Wolves occupy

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a very important niche in the 
Yellowstone ecosystem.

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And a niche simply refers to,

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what is an organisms role in 
its environment?

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What does it do?

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Who does it interact with, and how?

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What are its needs?

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So, really, the needs and the...

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interactions of an organism

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in an ecosystem

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describe this concept of a niche.

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Basically, everything about how

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it acts in that ecosystem.

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If there is overlap of a niche,

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a place where needs and roles overlap,

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

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Competition is going to take place

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when two organisms,

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two species,

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or two members of the same species

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

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So, for example, here we have a 
little parakeet

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and a starling that are fighting 
over a french fry.

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Now, hypothetically...

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in the case of competition,

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

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--from that resource--

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and we refer to this as 
competitive exclusion.

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Organisms can compete for lots of things.

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They can compete for space,

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like these corals.

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Um...

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the corals are also competing 
for sunlight.

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

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

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can't get it.

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So organisms can compete for physical 
resources like:

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

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Organisms can compete for food.

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The lions and hyenas are competing 
for food here.

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

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There was some very interesting
competitive interactions taking place.

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Organisms can compete for mates.

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These are two male elephant seals,

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

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

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all the females on the beach.

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Elephant seals have a harem mating system

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

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for that evolutionary fitness, for that
reproductive success,

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that is a very hotly contested position.

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

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

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have a little bit of disruptive selection.

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

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But, there is very intense competition 
for mates.

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When organisms compete

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they can compete in different ways.

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

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And we refer to this as exploitation 
competition.

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

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

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

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This squirrel is hoarding nuts.

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

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

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

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and doesn't allow other organisms to 
access it.

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Interference competition, 
on the other hand,

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

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with one another for a resource.

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This is sometimes referred to as 
"contest competition."

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

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

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

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and just setting them aside,

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instead what we have is an actual, 
physical altercation,

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a fight if you will, for that resource.

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So, exploitation competition: 
using up the resources.

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Interference competition: physically 
competing over them and--and

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physically keeping other organisms from
having them.

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So those are two different strategies 
for competition.

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

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of those take place.

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The coral example here, we have the 
algae is engaging

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in exploitation competition by

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covering up the coral and keeping it 
from getting light.

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The elephant seals are engaging in 
interference competition

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by physically battling one another

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for the mates.

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Okay...

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When competition occurs

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one of the things that we see

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is that one competitor,

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if they have the same exact needs,

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will often out compete the other 
predator.

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So here are two protists.

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Um , Paramecium aurelia and
Paramecium caudatum.

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That, if grown in separate flasks,

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in separate conditions,

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we see almost the exact same 
population growth curves.

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They grow in the same way.

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If, however, we put them in the same flask

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Paramecium aurelia ultimately out competes
Paramecium caudatum

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because two organisms cannot occupy
the same niche simultaneously

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and continuously.

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This is known as competitive exclusion.

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

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

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

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

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How organisms get around this is through 
resource partitioning.

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For example:

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this is a group of birds, warblers, 


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a closely related species,

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that are engaging in 
resource partitioning.

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They use different resources

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to allow them

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to effectively coexist.

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

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

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of the tree.

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

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They eat different things.

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

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small worms and grubs.

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

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So we have different forms of competition

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different types of resources being
used here.

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Different spaces, different food items...

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And so these birds have engaged
in resource partitioning

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where they take advantage of 
different resources

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

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One of the things we might see 
here though is that

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

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as desirable as others.

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

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we might see changes.

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

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Here is an example from the 
Oregon Coast.

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

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we have barnacles

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and we have mussels.

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

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

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during a portion of the day .

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And mussels tend to be very quickly 
growing.

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

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-and you see this happening here-

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they can crush and squeeze out barnacles.

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They are engaging in some exploitation 
competition where they are physically

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

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The problem that mussels have

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is that...

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while they are competitively excluding 
these barnacles

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they are limited to the area

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that is covered by water for much 
of the day.

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

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And so we see this very distinct,

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what's called a zonation line,

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that's separating the mussels and the 
barnacles

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because barnacles can live in those
higher, inner tidals

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

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So this is a good example of resource 
partitioning.

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

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

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

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in the high inner tidal.

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What's kind of exciting

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is that if mussels are removed in some way

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then barnacles will spread

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to fill the available space.

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

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removes and eats the mussels,

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barnacles will then spread to fill 
that available space

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and this is known as 
"competitive release."

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Basically if a superior competitor 
is removed

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

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They don't have to resource partition 
anymore.

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

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00:10:06,574 --> 00:10:08,533
species on the Oregon Coast

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00:10:09,018 --> 00:10:10,952
and throughout the Pacific Northwest

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00:10:10,952 --> 00:10:15,027
because they wipe out big mussel 
populations and allow other kinds of

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00:10:15,027 --> 00:10:16,963
organisms to live in the inner tidal.

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00:10:17,714 --> 00:10:20,115
So, competition has a really big 
influence here,

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00:10:20,617 --> 00:10:24,342
but if our sea star comes along and 
removes that superior competitor,

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00:10:24,702 --> 00:10:26,104
it changes the community--

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00:10:26,109 --> 00:10:29,262
making the sea star another example
of a keystone species.

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00:10:31,692 --> 00:10:35,887
And you can see that here in this 
actual picture of the, um, these sea stars

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00:10:35,887 --> 00:10:38,838
that come up to a certain level of the 
inner tidal

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00:10:39,128 --> 00:10:41,512
they've eaten a whole bunch 
of these mussels.

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00:10:42,782 --> 00:10:45,152
Remember from our example of
co-evolution,

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00:10:45,152 --> 00:10:49,757
sea stars are great at eating shellfish
because they pry open that shell

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00:10:49,757 --> 00:10:50,800
just a little bit

209
00:10:50,800 --> 00:10:54,853
and push their stomachs inside out and
inside that shell and--and dissolve those

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00:10:54,853 --> 00:10:57,143
nutrients in there and then
[clicks tongue]

211
00:10:57,143 --> 00:10:59,243
pull their stomachs back into their 
bodies.

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00:10:59,908 --> 00:11:04,168
So, here they have created this 
line of mussels and if you look below

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00:11:04,168 --> 00:11:07,343
the mussel line you can see all these
different kinds of seaweed,

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00:11:07,343 --> 00:11:09,202
there's some other shells downs here,

215
00:11:09,202 --> 00:11:10,113
some barnacles.

216
00:11:10,113 --> 00:11:12,458
And they have really changed the 
community.

217
00:11:13,563 --> 00:11:16,730
And we have different populations 
taking part in that community.

218
00:11:16,824 --> 00:11:17,991
We have mussels,

219
00:11:17,991 --> 00:11:19,416
we have sea stars,

220
00:11:19,618 --> 00:11:21,112
we have barnacles,

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00:11:21,112 --> 00:11:22,560
we have algae,

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00:11:22,560 --> 00:11:24,298
all of those populations,

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00:11:24,298 --> 00:11:27,114
all the members of a species that are 
living together in a place

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00:11:27,114 --> 00:11:28,593
are interacting...

225
00:11:29,107 --> 00:11:30,496
in this community.

226
00:11:30,496 --> 00:11:31,920
And what we are going to see

227
00:11:31,920 --> 00:11:33,636
is that competition

228
00:11:33,636 --> 00:11:36,092
can occur between members of a 
community.

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00:11:36,661 --> 00:11:38,742
Like a lion and a crocodile.

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00:11:40,410 --> 00:11:44,031
And, in this case, what are a lion and 
a crocodile gonna compete for?

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00:11:44,121 --> 00:11:46,544
Well, they're certainly competing for 
food.

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00:11:46,544 --> 00:11:49,521
But, they may not be competing for 
all of the same things.

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00:11:50,048 --> 00:11:52,700
So here we have niche overlap that is 
just partial .

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00:11:52,779 --> 00:11:54,800
In this case, the lion and the crocodile

235
00:11:54,800 --> 00:11:57,192
they're not competing for the same 
place to live;

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00:11:57,192 --> 00:12:00,296
the crocodile prefers an aquatic 
environment, the lion does not.

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00:12:00,296 --> 00:12:02,365
They're certainly not competing for mates.

238
00:12:03,595 --> 00:12:04,668
However...

239
00:12:05,261 --> 00:12:10,402
lions are going to have 100% niche overlap
with other members of the same species.

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00:12:11,246 --> 00:12:16,052
And so competition tends to be much 
more intense between members

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00:12:16,052 --> 00:12:17,629
of the same species.

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00:12:17,629 --> 00:12:21,210
That's the difference between 
interspecific competition:

243
00:12:21,210 --> 00:12:24,612
competition that takes place between 
members of a different species

244
00:12:25,436 --> 00:12:30,734
and intraspecific competition that takes
place between members of the same species.

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00:12:31,366 --> 00:12:34,026
And the real difference here is 
complete niche overlap.

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00:12:34,460 --> 00:12:35,895
If you're in the same species

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00:12:35,895 --> 00:12:37,559
you're competing for food,

248
00:12:37,559 --> 00:12:38,734
for living space,

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00:12:38,734 --> 00:12:39,797
for mates,

250
00:12:39,797 --> 00:12:41,667
because you have the exact same needs.

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

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is that intraspecific competition tends to
be the most intense competition

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and is going to be much more intense,

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in many cases,

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than interspecific competition.

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

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influence the shape,

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and size of these pop...

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

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

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

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your 5 activity points
and to also participate in the discussion

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

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I will also be asking and 
answering questions

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