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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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species on the Oregon Coast
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and throughout the Pacific Northwest
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because they wipe out big mussel
populations and allow other kinds of
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organisms to live in the inner tidal.
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So, competition has a really big
influence here,
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but if our sea star comes along and
removes that superior competitor,
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it changes the community--
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making the sea star another example
of a keystone species.
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And you can see that here in this
actual picture of the, um, these sea stars
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that come up to a certain level of the
inner tidal
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they've eaten a whole bunch
of these mussels.
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Remember from our example of
co-evolution,
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sea stars are great at eating shellfish
because they pry open that shell
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just a little bit
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and push their stomachs inside out and
inside that shell and--and dissolve those
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nutrients in there and then
[clicks tongue]
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pull their stomachs back into their
bodies.
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So, here they have created this
line of mussels and if you look below
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the mussel line you can see all these
different kinds of seaweed,
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there's some other shells downs here,
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some barnacles.
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And they have really changed the
community.
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And we have different populations
taking part in that community.
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We have mussels,
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we have sea stars,
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we have barnacles,
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we have algae,
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all of those populations,
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all the members of a species that are
living together in a place
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are interacting...
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in this community.
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And what we are going to see
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is that competition
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can occur between members of a
community.
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Like a lion and a crocodile.
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And, in this case, what are a lion and
a crocodile gonna compete for?
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Well, they're certainly competing for
food.
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But, they may not be competing for
all of the same things.
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So here we have niche overlap that is
just partial .
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In this case, the lion and the crocodile
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they're not competing for the same
place to live;
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the crocodile prefers an aquatic
environment, the lion does not.
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They're certainly not competing for mates.
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However...
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lions are going to have 100% niche overlap
with other members of the same species.
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And so competition tends to be much
more intense between members
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of the same species.
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That's the difference between
interspecific competition:
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competition that takes place between
members of a different species
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and intraspecific competition that takes
place between members of the same species.
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And the real difference here is
complete niche overlap.
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If you're in the same species
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you're competing for food,
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for living space,
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for mates,
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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.