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So, today we're going to continue
with our series of lectures to come

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to a conclusion from the section on
population and community ecology.

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At last time, or three lectures ago,
we were talking about the regulation

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of population growth.
And this time,

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we're going to move into,
just wanted to make sure the boards

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are in order, community ecology.
And as I said of the first lecture,

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this is one of the most difficult
branches of the ecological sciences

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to really describe because an
ecological community is a bit of an

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abstract concept.
And one definition is that it's a

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collection of species that are
linked together by their

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feeding relationships.

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OK, so it's sort of like the
ecosystem without the

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biogeochemistry in a sense.
So really what we're looking at

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here is the interaction between
species in a localized area with

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respect to how they influence each
other's fitness, in a sense.

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And these interrelationships between
these species govern all of the

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things that we talked about in the
first half of my lectures set.

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It's these interactions that shape
the biogeochemistry of those systems.

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So, this is the structure of the
system and the biogeochemistry is

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the function of the system.
And it's also these interactions.

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So, they affect the flow of energy,
which we talked about.  They affect

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the cycling of elements.
They affect the evolution,

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the very evolution of species within
the community.

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And these communities self assemble.
In other words, if you start with

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an empty plot of bare land,
we talked about this.  Remember the

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example of the glacier retreating
and showing the succession of

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species as the glacier retreated?
We started with a bare rock, and

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you'll start getting lichen
growing on the rock.

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And then that lichen will create a
little bit of soil,

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allowing plants to come in,
and that the plants increase

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productivity.  Some of them bring
nitrogen and, allowing shrubs and

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trees and everything.
And that's the self-assembly of the

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community.  Once you have plant
there, you can have insects there.

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Once you have insects there, you
have birds there.

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It self assembles.
And one of the questions that

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ecologists ask is, how deterministic
is that?

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I mean, we know there are some
random components to it,

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and we know that there are some
things that will happen because we

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see it happen over,
and over, and over.  So the big

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question is what must happen?
What could happen?  And what might

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not ever happen?
That's really one of the challenges

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of ecologists is to understand those
assembly rules

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of community if there are any.
Now, we're not going to really get

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into that.  We are just going to
start looking at the real

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fundamentals of community [SOUND
OFF/THEN ON] which is,

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what are the possible interactions
between species that shape

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evolution?  OK.

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Species interactions: so,
when we talk about species

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interactions and how they structure
communities, we have to first define

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some terms.  One is
Darwinian fitness.

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And the fitness of an individual is

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the relative ability of an
individual in a population to

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survive and reproduce.

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So, it's all relative,
OK, within a population.

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And we're going to define also,
we'll be talking about adaptations,

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and I know you know what this is,
but let's just make sure that we are

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all operating with the
same assumption.

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And an adaptation,
which is something that affects the

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fitness, is a heritable trait that
increases the fitness of an

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individual with respect to other
individuals in that population.

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So, these are just some operating
assumptions so that when we talk

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about species interactions,
there are several possibilities.

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If we have organism one and organism
two, we can have,

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and we ask how does the presence of
organism two and the presence of

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organism one affect the fitness of
the two organisms?

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And if the fitness of both
organisms is increased by being in

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the presence of the other,
that's called mutualism.

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Being together increases the fitness
of both relative to when they're

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alone.  If being together decreases
the fitness of both,

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that's called competition.
And if you have the situation,

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what we recall that?
It could be parasitism,

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yeah, parasitism.  What else?
Was the ultimate form of reduced

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fitness?  Predation,
yeah, being dead is the ultimate

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reduced fitness.  So, parasitism
and predation.

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And then there are some other sort
of rather vague interactions where

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when you put two individuals
together, the fitness of one is not

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influenced but the fitness of the
other is either influenced

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positively or negatively,
and we're not going to talk about

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those.  But this one's called
commencalism.  And this one's

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called amensalism.
And obviously there are gradients.

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Actually, an example of
commencalism is something that we've

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talked about.  Can anybody think
about what that is when we talked

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about food webs?
It's kind of a stretch,

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but detritivory.
An organism eating detritus,

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in a sense, is commencalism because
it doesn't affect the fitness of the

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dead individual because it's already
dead.  So, that gets to not having

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that much meaning.
So anyway, these we are not going

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to spend time on,
but they are forms of interaction

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that do exist.
And there are gradients between

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these.  Obviously, it's not
all black and white.

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So, we're going to start by talking
about competition.

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And just to remind you,
competition comes in two forms.

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There is intraspecific competition,
which means within a species, OK?

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And that's not what we're going to
be talking about today,

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but we've already talked about this
without explicitly,

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remember our logistic equation
and the density dependent feedback

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mechanisms in that population that
caused the population to deviate

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from exponential growth was due to
intraspecific competition:

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individuals within a species
competing with each other for

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resources.  We are going to talking
about now is more interspecific --

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-- which is competition

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between species, OK?
So, I want to show you some slides

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that are just from your textbook,
but just to get you in the mood for

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competition.  So,
it comes in all different forms,

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and I don't care whether you know
the names of these.

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It doesn't matter.  This is just to
give you an idea of the different

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types of competition that we see in
nature.  This is what's called

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consumptive competition,
and this is just showing the roots

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of the trees competing for nutrients
in the soil.  Preemptive competition

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shows these are barnacles.
We're going to talk a little bit

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more about that later,
just totally taking over the

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substrate.  So no other organism
could possibly settle there.

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Overgrowth competition in plants
where this plant would be shading,

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so other plants that require a lot
of light could not grow underneath.

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Chemical competition also occurs
where one plant will actually

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excrete certain chemicals that
create these corridors of no growth

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around them so other plants can't
get near to compete

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for the nutrients.
The classic form of competition,

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say, in birds and a lot of higher
organisms is competition for

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territory.  So these are displays so
that an individual can keep a

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certain territory,
and therefore make that food

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available to itself,
therefore increasing its fitness

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because it's able to
feed its young.

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And then this is sort of the classic,
really tooth and claw competition

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where encounter competition where
all these species are competing over

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this zebra carcass,
hyena, vultures, etc.

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OK, now before we can talk more and
more in detail about competition,

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we need to define the ecological
niche.

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And this is an interesting concept
in ecology that has been around for

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quite some time,
and it kind of went out of

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popularity for a while.
And I was gratified to see that

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it's made it back into the
introductory biology textbooks

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because I think it's a very
profound concept.

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In this particular competition,
the fundamental ecological niche

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comes from G. Evelyn Hutchinson,
who is one of the founders of modern

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ecology.  He defined as the
fundamental niche of an organism as

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an N-dimensional hypervolume,
every point on which a species can

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survive and reproduce indefinitely
in the absence of other

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species, OK?
So, this is an abstract concept,

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because those species are rarely in
the absence of other species,

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except maybe in a test tube.  But it
defines the, and also we can't even

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think about N-dimensions,
right?  We're able to think about,

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we can envision three dimensions.
But what he's talking about here,

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is every single dimension in the
environment that would have any

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effect on the fitness
of an organism.

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So here, just to wrap our brains
around this, we're looking at three

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dimensions.  Our organisms here is a
ladybug, and this would be food size.

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These guys eat little aphids and
things.  I don't know if you've ever

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used them under house plants,
but it's a good way to keep aphids

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off your house plants if you want to
introduce ladybugs to your dorm room,

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which maybe you don't.
But there's a certain range of size,

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food size, that they can eat.
And so, that's three dimensions.

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There are undoubtedly many other
dimensions that we don't even know

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about, elements that they require,
etc.  So, this would be everywhere,

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in this space is a space where this
organism could survive and reproduce

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indefinitely.  And the reason this
concept lost favor is its something

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you could never ever measure this
because we can't know

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the N-dimensions.
Well, you can never say you can't

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know anything,
but it's very difficult to say you

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could know all the dimensions that
influence the fitness of an organism.

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But it's still a very important
concept for thinking about it.

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And the niche is not a physical
place, OK?  The niche of an organism

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is not a physical place.
In an N-dimensional hypervolume.

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It's an abstract concept.  So this
is the fundamental niche,

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and here's another closely related
species whose niche has some overlap

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with this one,
but has different ranges for

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temperature, humidity,
and food size.  And when you have

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overlapping niches is when you have
the possibility,

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the potential, for competition.
And two things can happen.

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If they overlap a lot,
than those two species cannot

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coexist in the same environment.
One will outcompete the other, and

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it will move on to some other place
where it doesn't have a strong

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competitor.  But if they overlap a
little, you can actually have

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competitive coexistence.
And we're going to talk about the

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results of these degrees of niche
overlap as we go on in the lecture.

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So, if the species can makes it
realized, so this is its fundamental

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niche, this one's fundamental niche,
and what happens if it can make its

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realized niche small enough so that
there's no niche overlap,

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then you can have coexistence of
those two species,

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or very little niche overlap in the
same environment.

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So that's the difference between
the fundamental and the

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realized niche.
I think this is from your textbook.

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This is just one dimension, seed
sized, for, say,

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a bird eating seeds of this size
range.  We'll be talking about birds

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a lot in this.
And here's partial niche overlap,

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species to where they eat some seeds
of the same size,

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but by and large the mode is
different.

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You can have species coexisting.
Partial niche overlap can lead to

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competitive coexistence.
And here's the complete overlap in

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just this one dimension,
which would lead to competitive

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exclusion.  But obviously it matters
what's happening on all the

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dimensions.  This is just an
oversimplification, to

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give you the idea.
OK, so before we go to that,

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I want to talk about the classic
experiment that led to this,

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they're going to put this screen up.
Screen, screen, screen, screen.

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Can you see, or do I need to turn

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the lights on?
Thank you.  I'm sorry,

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I always ask my questions that way,
where there's no possible answer.

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There were some classic competition
experiments that's carried out by

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Gause way back in 1934 --
-- that I'm just going to use to

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illustrate the concept of
competitive exclusion,

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because these were done with very
simple protozoa in a test tube,

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paramecia, and actually this was
back in the days when they were

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developing these theories for
population growth.

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And these organisms were growing
according to the logistic equation.

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So here we are with,
and this is the classic experiment

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actually in your textbook that they
talk about in the context of the

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ecological niche.
So this is Paramecia caudatum.

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These names aren't important.
Don't worry about it,

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but we have to call them something.
P. aurelia, which, when grown alone

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in a test tube grow according to the
logistic equation,

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they grow up and then they level off
at a certain level.

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And what Gause did is that he wanted
to see, look at this phenomenon of

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competition and he grew them
together, and he found that,

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actually that no matter what
combination he put in,

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aurelia would always win out in
competitive exclusion.

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And he learned through a series of

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experiments, we don't have time to
go into the details,

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but this would always occur if you
made two species compete in a very

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simple environment.
In the test tube where he was

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feeding these guys exactly the same
food, some form of bacteria,

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in a test tube this one would always
outcompete the other,

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and there would be competitive
exclusion.  If he made the

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environment more complex,
where there were layers in it,

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or there was sediment in the bottom
of the test tube,

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that allowed more niche dimensions.
There were conditions under which

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the competitive coexistence would be
allowed.  And he actually developed

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00:24:10,000 --> 00:24:15,000
a set of equations to describe his
competition that I'm going to write

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00:24:15,000 --> 00:24:20,000
for you.  We're not going to use
them; we're not going to analyze

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them in detail,
but I'm just going to show them to

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00:24:26,000 --> 00:24:31,000
you so that you have an appreciation
for how population ecologists and

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community ecologists start to think
about these systems.

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So, he said we can model this
interaction using our logistic

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equation.  So he said dN/dt would be
the growth rate of,

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let's call, the top one,
one.  It doesn't matter what you

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00:24:57,000 --> 00:25:04,000
call which.  The dN/dt equals r1,
N1.  Now here's our logistic, K1

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00:25:04,000 --> 00:25:11,000
minus N1 over K.
But he said I'm going to modify this

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00:25:11,000 --> 00:25:18,000
equation so that the actual growth
of the organism is reduced to some

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00:25:18,000 --> 00:25:25,000
amount that's proportional to the
number of the other organisms that

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are there.  So, he called
that alpha-N2.

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OK, so some amount that's
proportional to amount the other

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species that's here.
And then, he said dN2/DT is equal

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to r2, N2, K2 minus N2 minus beta-N1
over, this should be K1, over K2.

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So, the growth rate of species to in
the presence of species one is

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00:26:05,000 --> 00:26:10,000
reduced by some amount that's
proportional to the abundance of

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00:26:10,000 --> 00:26:15,000
species one.  And these,
the values of these, these are

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00:26:15,000 --> 00:26:20,000
called competition coefficients.
You can actually do experiments and

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00:26:20,000 --> 00:26:26,000
put values on these,
and they are a measure of how strong

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00:26:26,000 --> 00:26:31,000
a competitor each of these species
are with respect to

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the other one.
So, you're not going to have to deal

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00:26:36,000 --> 00:26:41,000
with these, but I just wanted you to
see them, and see how population

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00:26:41,000 --> 00:26:46,000
ecologists began to model these
systems.  And so,

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00:26:46,000 --> 00:26:52,000
it's the relative values of these
relative to the carrying capacities

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00:26:52,000 --> 00:26:57,000
that will ultimately determine
whether species will coexist or not

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00:26:57,000 --> 00:27:02,000
when they are competing.
OK, so that's more of a theoretical

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00:27:02,000 --> 00:27:07,000
analysis.  Now let's look at the
real world.  Competitive exclusion,

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00:27:07,000 --> 00:27:12,000
that is, the exclusion of one
species from an environment because

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00:27:12,000 --> 00:27:16,000
of strong competition in another,
is very difficult to study, because

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00:27:16,000 --> 00:27:21,000
if it's not there,
you don't know it was excluded,

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00:27:21,000 --> 00:27:26,000
right?  I mean, you don't go to some
place and say I don't see

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00:27:26,000 --> 00:27:31,000
the species here.
It must have been eliminated by

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00:27:31,000 --> 00:27:36,000
competitive exclusion.
It might never have been there.

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00:27:36,000 --> 00:27:40,000
So, the way we learn about this
phenomenon is either through

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00:27:40,000 --> 00:27:45,000
inadvertent experiments,
and that is the introduction of

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00:27:45,000 --> 00:27:50,000
species to new environments and then
see what happens,

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00:27:50,000 --> 00:27:55,000
or actual intentional ecological
experiments.  So,

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we're going to talk about both of
those.

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And the first one --

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-- we'll talk about invasions --

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-- and competitive exclusion.
And one of the classic examples of

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00:28:33,000 --> 00:28:41,000
this is the zebra mussel.
I don't know what happened.

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00:28:41,000 --> 00:28:49,000
Oh, there it is.  I didn't realize
this was animated.

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00:28:49,000 --> 00:28:57,000
That's why there was nothing there.
So, the zebra mussel is a tiny

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mussel that was introduced to the
United States back in,

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00:29:05,000 --> 00:29:10,000
I guess, 1988.
And up here, introduced into the

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00:29:10,000 --> 00:29:14,000
Great Lakes by ships just being
attached to ships,

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00:29:14,000 --> 00:29:18,000
or it's possible it might have been
the larvae in ships' ballasts.

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00:29:18,000 --> 00:29:22,000
Ships go into port, they take on
water into their ballasts to

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00:29:22,000 --> 00:29:26,000
stabilize, and then they go to
another port and let it out.

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00:29:26,000 --> 00:29:30,000
And they're filled with larvae and
species.

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00:29:30,000 --> 00:29:37,000
So, the entire world oceans are now
filled with introduced species from

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00:29:37,000 --> 00:29:44,000
ships ballasts.
So here's 1988.

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00:29:44,000 --> 00:29:51,000
The zebra mussel is there.
1990: here.  92: here.  94,

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00:29:51,000 --> 00:29:58,000
90 whatever, oh, 2001.  It spread
amazingly fast.

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00:29:58,000 --> 00:30:04,000
And it is this tiny little mussel
that seems to thrive everywhere:

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00:30:04,000 --> 00:30:10,000
clogs, all kinds of pipes,
settles on top of other native

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00:30:10,000 --> 00:30:16,000
shellfish and kills them,
and has led to extensive competitive

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00:30:16,000 --> 00:30:22,000
exclusion of native shellfish in a
number of ecosystems.

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00:30:22,000 --> 00:30:28,000
Some of the effects of these: in
some ecosystems they cleared

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00:30:28,000 --> 00:30:34,000
up the water.
They are able to filter just an

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00:30:34,000 --> 00:30:39,000
amazing amount of water when they're
feeding.  So they actually have

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00:30:39,000 --> 00:30:43,000
increased the clarity of the water
in many ecosystems,

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00:30:43,000 --> 00:30:48,000
filtering out plankton,
which allows the light to penetrate

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00:30:48,000 --> 00:30:53,000
deeper in those systems,
allowing aquatic plants to grow from

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00:30:53,000 --> 00:30:58,000
the bottom.  So the introduction of
this one species can completely

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00:30:58,000 --> 00:31:03,000
change the structure of
the entire ecosystem.

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00:31:03,000 --> 00:31:06,000
I just heard a lecture.
I was just visiting the Institute

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00:31:06,000 --> 00:31:10,000
for Ecosystem Studies which is out
in Millbrook, NY.

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00:31:10,000 --> 00:31:14,000
By the way, if any of you are
looking for summer internships and

300
00:31:14,000 --> 00:31:17,000
are interested in ecology,
they have a fabulous summer

301
00:31:17,000 --> 00:31:21,000
internship program.
I've had several students go there

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00:31:21,000 --> 00:31:25,000
that have had great experiences.
But there's somebody there studying

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00:31:25,000 --> 00:31:29,000
the zebra mussel invasion
in the Hudson River.

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00:31:29,000 --> 00:31:33,000
And he showed this incredibly
depressing graph of over the last

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00:31:33,000 --> 00:31:37,000
ten years of the native mussels in
that river going down to basically

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00:31:37,000 --> 00:31:42,000
extinction.  And then,
this is the weird thing about

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00:31:42,000 --> 00:31:46,000
ecosystems, just last year it
started to turn around.

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00:31:46,000 --> 00:31:50,000
And they haven't done anything to
eradicate the zebra mussels,

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00:31:50,000 --> 00:31:55,000
but the native mussels are starting
to have a comeback.

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00:31:55,000 --> 00:31:59,000
And nobody knows why,
and nobody knows whether it's a real

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00:31:59,000 --> 00:32:04,000
comeback because it could come back
for a couple of years.

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00:32:04,000 --> 00:32:10,000
So, it's really interesting how
unpredictable these complex systems

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00:32:10,000 --> 00:32:17,000
are.  But these mussels can cause
millions and millions of dollars of

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00:32:17,000 --> 00:32:23,000
damage.  And I also learned on that
trip that ecologists are trying to

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00:32:23,000 --> 00:32:30,000
get in place policies that if an
industry for whatever reasons wants

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00:32:30,000 --> 00:32:36,000
to intentionally introduce,
Here's an example of an application

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00:32:36,000 --> 00:32:40,000
of fundamental ecological knowledge.
The reason people study the ecology

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00:32:40,000 --> 00:32:45,000
of invasive species,
understanding this competitive

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00:32:45,000 --> 00:32:49,000
exclusion and all that,
is that you want to use that

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00:32:49,000 --> 00:32:54,000
understanding to be able to predict,
if you introduce a new species to a

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00:32:54,000 --> 00:32:58,000
new habitat, whether it will be
invasive or not,

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00:32:58,000 --> 00:33:03,000
there are some species you can
introduce and they will fit right in

323
00:33:03,000 --> 00:33:08,000
and not exclude every
other species.

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00:33:08,000 --> 00:33:13,000
And so, what they're trying to put
in place is insurance that a company

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00:33:13,000 --> 00:33:18,000
would have to buy that was either
intentionally introducing a species,

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00:33:18,000 --> 00:33:23,000
or whatever practice that they were
doing was likely to introduce a

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00:33:23,000 --> 00:33:28,000
species, and the cost of that
insurance would be a function of the

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00:33:28,000 --> 00:33:34,000
probability of that species actually
causing competitive exclusion.

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00:33:34,000 --> 00:33:39,000
And this is something that people
are trying to put into place in to

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00:33:39,000 --> 00:33:45,000
the economic system basically.
So, it puts a new meaning to

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00:33:45,000 --> 00:33:50,000
limited liability company,
LLC.  So, you have to insure your

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00:33:50,000 --> 00:33:56,000
liability, which I think would go a
long way to reduce some of these

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00:33:56,000 --> 00:34:01,000
ecological crises.
OK, so that's an inadvertent

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00:34:01,000 --> 00:34:06,000
experiment.  Now there are many,
many examples of this.  There's

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00:34:06,000 --> 00:34:11,000
books written on invasive species.
And if I can get this thing to work,

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00:34:11,000 --> 00:34:16,000
I'll show you some clips of invasive
species, snakes.

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00:34:16,000 --> 00:34:20,000
And the biggest impact is on
islands because islands have been

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00:34:20,000 --> 00:34:25,000
isolated ecosystems for so long that
if you introduce a species,

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00:34:25,000 --> 00:34:30,000
you have dramatic changes.  In
Australia, a big example was a

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00:34:30,000 --> 00:34:35,000
prickly pear cactus which was
introduced many years ago to create

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00:34:35,000 --> 00:34:40,000
living fences for livestock.
They completely took over not all of

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00:34:40,000 --> 00:34:46,000
the grasslands,
but a lot of the grasslands and turn

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00:34:46,000 --> 00:34:51,000
them into thickets.
OK, so invasive species are

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00:34:51,000 --> 00:34:57,000
inadvertent ecological experiments.
Let's talk about intentional

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00:34:57,000 --> 00:35:02,000
experiments.  And this is also very
classic textbook experiment that was

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00:35:02,000 --> 00:35:08,000
one of the first ecological
experiments to be done.

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00:35:08,000 --> 00:35:12,000
And it was done with barnacles.
This was Joseph Connell was a

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00:35:12,000 --> 00:35:17,000
professor at the University of
California, Santa Barbara.

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00:35:17,000 --> 00:35:21,000
Barnacles have a larval stage that
floats around in the plankton,

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00:35:21,000 --> 00:35:26,000
and then they settle on rocks.  So
this was a classic barnacle

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00:35:26,000 --> 00:35:31,000
ecosystem in Scotland,
actually, in which the upper inner

352
00:35:31,000 --> 00:35:36,000
tidal there is a species
called Chthamalus.

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00:35:36,000 --> 00:35:40,000
And then the lower was dominated by
a species of mussel called Balanus.

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00:35:40,000 --> 00:35:45,000
So, he asked the question, is this
distribution where the two are

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00:35:45,000 --> 00:35:49,000
exclusive of one another,
is it due to competition between

356
00:35:49,000 --> 00:35:54,000
them, or is it just that this one
tolerates desiccation longer than

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00:35:54,000 --> 00:35:58,000
this one?  The inner tidal zone,
the tide goes up and down, so this

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00:35:58,000 --> 00:36:03,000
one's going to be exposed to dryness
a lot longer.

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00:36:03,000 --> 00:36:07,000
So, how do you answer that question?
Well, you do an experiment and so

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00:36:07,000 --> 00:36:12,000
what he did was he took rocks from
the upper, inner tidal that had the

361
00:36:12,000 --> 00:36:17,000
Chthamalus on them,
and he moved them to the lower one.

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00:36:17,000 --> 00:36:22,000
And he let the Balanus, the species
that dominates down here colonize on

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00:36:22,000 --> 00:36:27,000
those rocks.  But then he divided
them in half, and removed the

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00:36:27,000 --> 00:36:32,000
Balanus from half of the rock.
And then he monitored the

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00:36:32,000 --> 00:36:37,000
survivorship of the Chthamalus.
And remember the survivorship

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00:36:37,000 --> 00:36:41,000
curves that we talked about when we
created those life tables,

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00:36:41,000 --> 00:36:46,000
he actually measured survivorship
curves on these.

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00:36:46,000 --> 00:36:51,000
If you go to the original paper,
you see LX is a function of time.

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00:36:51,000 --> 00:36:56,000
So that's a tool that we use,
to ask the question, is the

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00:36:56,000 --> 00:37:01,000
survivorship of Chthamalus increased
in the absence of Balanus?

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00:37:01,000 --> 00:37:05,000
And this is all from your textbook,
showing that the percent of

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00:37:05,000 --> 00:37:09,000
mortality, when a competitor is
present is much higher than the

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00:37:09,000 --> 00:37:14,000
competitor is absent.
So, he's able to show directly that

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00:37:14,000 --> 00:37:18,000
there was competition between the
two.  And in fact,

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00:37:18,000 --> 00:37:23,000
this was that kind of aggressive
kind of competition where one just

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00:37:23,000 --> 00:37:27,000
plucks the other one off the rock.
I mean it's direct: you're on my

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00:37:27,000 --> 00:37:32,000
rock; get out of here,
and it pops it off.

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00:37:32,000 --> 00:37:37,000
He also was able to show that
tolerance to desiccation is also a

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00:37:37,000 --> 00:37:42,000
factor in this system.
It's not like it's totally

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00:37:42,000 --> 00:37:47,000
competition.  But competition was
playing a role,

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00:37:47,000 --> 00:37:52,000
and so I've summarized that in this
slide using our terminology.

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00:37:52,000 --> 00:37:57,000
He was able to show that the
fundamental niche of Chthamalus,

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00:37:57,000 --> 00:38:05,000
in other words --
-- the region in the inner tidal,

384
00:38:05,000 --> 00:38:15,000
where the larvae could actually
settle and live in the absence of

385
00:38:15,000 --> 00:38:25,000
competitors was much broader than
the realized niche.

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00:38:25,000 --> 00:38:36,000
All right, so let's get this over.
This is from your textbook.

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00:38:36,000 --> 00:38:50,000
And we're going to just use,
I'm going to use an example of that.

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00:38:50,000 --> 00:39:04,000
So, competition can also lead to
character displacement --

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00:39:04,000 --> 00:39:18,000
-- which in turn can lead to actual

390
00:39:18,000 --> 00:39:27,000
competitive coexistence.
And an example of this, we're going

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00:39:27,000 --> 00:39:37,000
to talk about Darwin's finches in
the Galapagos Islands.

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00:39:37,000 --> 00:39:46,000
And one of the ways that ecologists
actually measure,

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00:39:46,000 --> 00:39:56,000
that's a bird, in case you didn't
notice it.  And this

394
00:39:56,000 --> 00:40:04,000
is beak depth.
The shape and size of a beak tells

395
00:40:04,000 --> 00:40:11,000
you what kinds of seeds a bird can
eat, and so they measured beak depth

396
00:40:11,000 --> 00:40:18,000
as a niche dimension,
basically, because it tells you what

397
00:40:18,000 --> 00:40:26,000
size seeds the bird can eat.
And a study was done; we're going

398
00:40:26,000 --> 00:40:33,000
to make the islands here.
What is going to call them A,

399
00:40:33,000 --> 00:40:41,000
B, C, D; these are islands.
And there are two species of finches,

400
00:40:41,000 --> 00:40:49,000
which we are just going to call F.
Well, they're fuliginosa.  Again,

401
00:40:49,000 --> 00:40:57,000
the name's not important,
and the other one is called fortis.

402
00:40:57,000 --> 00:41:05,000
So, we'll just call them,

403
00:41:05,000 --> 00:41:12,000
on islands that have both of them,
and there are some islands that have

404
00:41:12,000 --> 00:41:18,000
only one.  So,
what was done is they measure the

405
00:41:18,000 --> 00:41:25,000
beak depth of the different finches
on the islands where they were found

406
00:41:25,000 --> 00:41:32,000
together versus islands where they
were found alone in the

407
00:41:32,000 --> 00:41:40,000
Galapagos Islands.
And what they found,

408
00:41:40,000 --> 00:41:48,000
and this has been shown for many,
many different studies.  You look at

409
00:41:48,000 --> 00:42:07,000
the beak depth distribution.

410
00:42:07,000 --> 00:42:23,000
This is percent in size class.
And this is island C, D, and A,

411
00:42:23,000 --> 00:42:34,000
and B.
And they found that when the species

412
00:42:34,000 --> 00:42:42,000
were on islands where they lived
alone, they had almost complete

413
00:42:42,000 --> 00:42:49,000
niche, oh this is beak depth.
They had exactly the same size beak

414
00:42:49,000 --> 00:42:57,000
distributions.
In other words,

415
00:42:57,000 --> 00:43:05,000
they were feeding on the same food.
And on the islands where they were

416
00:43:05,000 --> 00:43:13,000
together, A and B,
I'm just making sure this actually

417
00:43:13,000 --> 00:43:21,000
holds together,
they found what is called character

418
00:43:21,000 --> 00:43:29,000
displacement, and that is that the
birds that had longer beaks and

419
00:43:29,000 --> 00:43:37,000
smaller beaks,
were preferentially selected for

420
00:43:37,000 --> 00:43:45,000
such that reducing the amount
of niche overlap.

421
00:43:45,000 --> 00:44:03,000
So, and this leads to competitive
coexistence.

422
00:44:03,000 --> 00:44:07,000
OK, and that's what we're looking at
here.  This is from your textbooks.

423
00:44:07,000 --> 00:44:12,000
This is from African seed crackers
showing that birds with smaller

424
00:44:12,000 --> 00:44:16,000
bills consume soft seeds more
efficiently.  Birds with larger

425
00:44:16,000 --> 00:44:21,000
bills crack hard seeds,
and you can see that the width of

426
00:44:21,000 --> 00:44:24,000
the bill here is different.