WEBVTT

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OK, so the last lecture we were
talking about competition,

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and the result of competition
between organisms.

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And I didn't quite finish,
so I just want to finish up on that

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lecture, and then will move on to
predation, an interaction between

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two species which results in
increasing the fitness and one,

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and decreasing the fitness in the
other. But let's just finish up

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with competition.
We were talking about character

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displacement and beak depths.
And we have shown that when you

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have two closely related birds with
the same beak size,

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if they live on islands separate
from one another,

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they compete for the same food.
But if you live on an island

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together, what happens is that you
have this character displacement

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where the beak of what will get
bigger and the beak of the other

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will get smaller.
So they can exploit different food

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resources. And this character
displacement is the beginning of

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species formation.
And this is very common on islands.

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And these are the famous finches
from the Galapagos Islands that

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Darwin first based his theory of
evolution, or it was an important

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part of his theory of evolution,
where he realized that there must

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have been an ancestor finch,
that all of these other finches that

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had different representation on
different islands evolved from

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through the slow change in traits
that is selected as a result of

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different combination of species
being together or alone in different

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islands. And this is what's called
adaptive radiation.

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And this is really a powerful
mechanism for evolution.

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This is the Galapagos finches,
but you also see this in an extreme

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form in Hawaii among the honey
creepers showing this incredible

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diversity of beak types that have
evolved to exploit different

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kinds of food.
OK, so before we go on to predation,

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I just want to walk you through an
evolutionary scenario,

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so that you can see how this might
work on an island,

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Archipelago. So this is the
mainland, and we're going to start

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with an ancestor species,
A, and our Archipelago is going to

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have three islands.
OK, let me draw this.

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Here's the same three islands.

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So this is time passing.
So as we move,

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these are the same three islands as
a function of time passing,

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OK? So at the beginning, we're
going to have our founder species

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flying and colonizing the island.
OK, so A is on this island. And so,

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the first thing that happens is that
A evolves and becomes B.

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So each one of these is just the
name of the species,

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OK? This is species A,
species B, through what's known as

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the founder effect.
And that is when you have a few

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members of the species colonizing on
this island. You have a tiny gene

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pool, and the genetic composition of
this drifts such that it actually

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becomes a different species from the
one on the mainland.

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So, A becomes B.
So the full arrow means becomes B

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on the islands through the founder
effect. And now,

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we're going to have B migrate to a
new island. So,

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A is now B on this island,
right?

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And B is going to colonize this
island. And through that same

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founder effect,
B becomes C. So let me just write

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what's happening here.
B becomes C. I think you can see

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what's happening on one island,
and then it migrates back.

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So, let's let C migrate back to
where B is, and C also founds a new

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island. So, we're going
to let C migrate here.

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So we end up with C and B here now
able to compete with each other,

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C here and C here. OK, so we've got
a new combination of species,

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and we are going to let C become D
here due to the founder effect,

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and D is going to migrate over to
this island.

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So, C becomes E when with B because
of character displacement.

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So, C becomes E here when it's with
B. So you end up with E and B on

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this island. D is going to migrate
to this island.

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So, we have C and D here.
And, C has evolved to be D here.

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So, we also have C becomes D when
alone.

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OK, so this is just a scenario we
are making up.

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OK, you can make up any scenario.
But it's to give you the idea of

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how this adaptive radiation comes
about. So, starting with one single

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species on the mainland,
if you have an island archipelago

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where species can be isolated enough
from each other to restrict,

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but not completely eliminate,
the gene flow you can have this

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rapid adaptive radiation.
So, evolutionary biologists often

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study islands in order to study this
phenomenon. OK,

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so just to summarize for competition,
interspecific

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competition results in

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either competitive coexistence,
which can be achieved either through

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niche differentiation.
Do you remember,

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what was an example of that last
time? The barnacles and the inner

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tidal. One took the high road,
and one took the low road. That's

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called niche differentiation,
or character displacement.

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And this can happen very rapidly.
I hesitate to tell you about really

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interesting things that you don't
have to know, but I will anyway.

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This is really interesting study by
a couple at Princeton of the

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Galapagos finches.
And they've shown that you can have

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character displacement of the
islands over a period of one or two

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years, just depending on
the amount of rainfall.

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So, it can happen very rapidly by
just selecting for different

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character traits,
or competitive exclusion,

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which is the case where the niche
overlap is so great that one of the

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species completely outcompete
the other.

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The example from last time was the
zebra mussels and Gause's paramecia

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in the test tubes excluding the
other. So, these are really

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important ecological and
evolutionary forces.

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The other thing I learned from your
comments, which I was very heartened

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by, is that at least one person
really liked the definition of the

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niche, of the N-dimensional hyper
volume, which I have always loved

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and I think is fundamentally
important because people throw

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around ecological niche in everyday
language and think of it as a place

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in the environment.
And I think that a more robust

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definition is so much more useful.
So, let's move onto predation,

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which is a very strong evolutionary
force. It can control population

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dynamics. It can shape community
structure. We're going to talk

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about each of these.
It actually influences competition,

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which in turn shapes community
structure. And it's a powerful

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evolutionary agent.
In other words,

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it's very important in influencing
naturally selection.

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So, let's start with the classic,
here's a classic predator-prey

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interaction. There is two wolves
and a moose being attacked.

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The wolves are not evil. They're
just getting their meal.

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OK, this is a very famous classic
study of the snowshoe hare,

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and lynx. Lynx is a cat:
populations in northern Canada.

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And these data were collected by
the Hudson Bay Company trapping

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records. So, it's really from the
amount of animals that were actually

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trapped that these abundances come
from. And that's where these

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coupled oscillations,
this is the hare, and this is the

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lynx showing these couples
oscillations with a roughly

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11 year cycle.
And people spend a lot of time

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trying to understand what was
driving that oscillation.

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And mathematicians love these
coupled oscillators.

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And so, the first attempt to model
this kind of thing was using a very

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simple model. Remember we said the
dN/dt equals rN?

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That's our exponential growth
equation. And we also said before

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the dN/dt or that r is equal to the
birthrate (b) minus the

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death rate (d).
OK, so grossly oversimplifying the

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system, the first set of equations
that were used to try to describe

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this, are if you use for the
predator, you call the predator

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dN1/DT equals b1,
1 minus d1,N1. OK,

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so that's just this equation.
And they said,

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well, how do we modify this equation
so that the growth rate of the

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predator is somehow a function of
the density of the prey?

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Well, the easiest thing to do is
just make it proportional,

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right? So what they do is put N2 in
there. So, the prey population is

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going to be dN2/dt,
and we're going to the same thing:

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b2,N2 minus d2,N2,
and the question is how do we modify

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the prey growth rate equation so
that it is somehow a function of the

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density of the predator?
So what would you do? So here,

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this says the birthrate of the
predator is influenced.

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As prey density increases,
the birthrate of the predator

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increases.
How would you modify this equation

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so that the predator density has an
effect on it? It's pretty obvious,

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but I'm trying to get you with me.
Exactly. It would be the death term.

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As the predator numbers increase,
the death term would go up.

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And it turns out that these are two
coupled differential equations that

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make a beautiful oscillatory system,
a couple oscillators, perfect

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oscillators like that. This
is predator density.

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So that would be N1,
N2, and this is time if you chart

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their density with time.
And how many of you have actually

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had this in the course?
Yeah, see? [LAUGHTER] And what

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courses have you had in it?
Differential equations, yeah.

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Mathematicians love it. But real
populations, predator and prey,

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don't really operate this way.
I mean, you see these oscillations,

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but rarely can it be attributed
solely to the interaction between

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the predator and the prey.
There's usually many other factors.

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So, and I'll just give you one
example. So ecologists go ahead and

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say, OK, so what's really going on?
And here's an example. It turns

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out that in many cases,
the food supply of the prey is

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oscillating.
OK, so the availability of food to

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the prey oscillates,
making the prey population oscillate,

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which then can drive an oscillation
in the predator population.

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So, it's more than just the
coupling between the two.

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There are also an external
oscillators driving both of them.

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And again, I'd like to try to
address the role of

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experimentation.
Here is an experiment done with

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rabbits. And I don't know what the
predator was. It might have been,

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I'm not sure the predator was, but
anyway, rabbits,

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in which through experimentation
they increased the food supply to

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the rabbits through fertilization.
And they showed that, so this is

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the control.
And this is the phase of the cycle

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in the hare population relative to
the density in the controls.

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So, showing that when the food
supply was increased,

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the oscillation was still there.
So, it wasn't only relieving the

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rabbits of food limitation,
did not eliminate the oscillation,

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but if you'd excluded the predators,
you still also had the oscillation

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there.
And if you did both of them,

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it increased the amplitude of the
oscillation, relative to the control.

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So the conclusion from this is that
both food supply and the predation

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affected the oscillation.
Another very classic experiment is

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the experiment by Huffaker back when
people began to be enamored of these

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coupled differential equations.
People wanted to test the hypothesis

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of those equations in the laboratory.
And they tried to set up

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predator-prey systems in the lab,
and see if they can get them to go

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in these coupled oscillations for
many cycles. And Huffaker set up a

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system of a predatory mite
and a prey mite.

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Ecologists like to use insects as
experimental systems because they're

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small and you can do it in the lab.
And this one lived on oranges.

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So it was an herbivorous mite.
And the predator obviously lived on

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mites. And he set up a very simple
system in the lab of oranges,

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and introduced the predator and prey,
and inevitably he got this,

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where prey would increase, and then
the predator would increase,

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and would overshoot, and the prey
would die, and the predator

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would die.
So he only got one cycle,

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with a simple system could not get
this to persist,

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well, that doesn't even qualify as a
cycle. So he realized,

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so this is a simple system.
And he had a grid,

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which is shown up here in which he
had oranges. And he had them

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interspersed with rubber balls to
have a little bit of complexity in

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the system. But he found with that
design, he could not get the system

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to persist. So he hypothesized that
the reason it wouldn't persist is

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that it's much too simple,
not close enough to nature.

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So he introduced all kinds of
complexity. He increased the size

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of his grid relative to the
populations, which would give the

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prey mites more of a chance to get
away from the predator.

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He put barriers of dispersal,
like Vaseline moats, and he actually

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put little launching pads for the
prey. I don't know what they look

00:23:26.000 --> 00:23:31.000
like, diving boards,
I don't know what they were,

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but little launching pads that just
increased a lot of complexity so

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that it gave the prey an ability to
move around relative

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to the predator.
And he was actually able to,

00:23:46.000 --> 00:23:52.000
this shows his results over 200 days.
He was actually able to get three

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full cycles of the predator-prey
oscillation. And up here,

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it just shows you that they're sort
of a cat and mouse game going on.

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It shows you the location of the
prey mites relative to the predator

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mites at these different points in
time of this cycle,

00:24:12.000 --> 00:24:16.000
showing that they're moving around
the system, and that the complexity

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allowed this coupled oscillator to
persist. And of course,

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we present this because it was a
classic experiment.

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It was a pioneering experiment,
but I mean, there have been a lot

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more since then.
And of course,

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it has implications for stability of
populations in the natural world.

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As we make the natural world less
and less complex,

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it reduces the ability of
populations that are engaged in

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these coupled oscillatory systems to
persist. It increases the

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likelihood of extinction.
So this was like a tiny little

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localized extinction in his
experimental system.

00:25:02.000 --> 00:25:15.000
Another classic example that's often
cited about the role of predation in

00:25:15.000 --> 00:25:28.000
regulating population dynamics has
to do with rubber plantations over

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here in Malaysia.
Did I spell that right?

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That looks wrong. Oh well,
is that OK? And I don't have any

00:25:42.000 --> 00:25:48.000
data for you. So this is just a
story, but it's very compelling,

00:25:48.000 --> 00:25:53.000
and there is data somewhere but I
don't have a slide.

00:25:53.000 --> 00:25:58.000
But, in the first half of the
century, in its rubber plantations

00:25:58.000 --> 00:26:04.000
in Malaysia they had a tremendous
diversity of insects,

00:26:04.000 --> 00:26:09.000
but didn't have any real serious
problems with insect pests in the

00:26:09.000 --> 00:26:15.000
rubber plantations.
And, in 1950, they had a small

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outbreak of defoliated caterpillars.
And that was right about the time

00:26:21.000 --> 00:26:27.000
that DDT was invented and
synthesized, and became available.

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And so, entomologists came down and
sprayed the plantation with DDT

00:26:33.000 --> 00:26:40.000
hoping to get rid of
this caterpillar.

00:26:40.000 --> 00:26:44.000
In the next year,
the outbreak got bigger.

00:26:44.000 --> 00:26:48.000
They sprayed more. The next year
the outbreak got bigger.

00:26:48.000 --> 00:26:52.000
They sprayed more, and finally the
whole thing was out of control.

00:26:52.000 --> 00:26:56.000
And they said what's going on here?
We are killing these things, and

00:26:56.000 --> 00:27:00.000
it's getting bigger.
To make a long story short,

00:27:00.000 --> 00:27:04.000
what they were doing, this is a
cocoon.

00:27:04.000 --> 00:27:12.000
Oh boy. How do you spell cocoon?
That's not right. Is that right?

00:27:12.000 --> 00:27:21.000
Anyway, you know what I mean.
Caterpillars live in cocoons,

00:27:21.000 --> 00:27:29.000
and there was a, that's a wasp with
a big, long organ that

00:27:29.000 --> 00:27:36.000
it lays its eggs.
It needs some legs,

00:27:36.000 --> 00:27:40.000
doesn't it? OK, I made some front
legs too. There.

00:27:40.000 --> 00:27:44.000
OK, so that's a wasp that lays its
eggs in these caterpillar cocoons,

00:27:44.000 --> 00:27:49.000
and in doing so, kills caterpillars.
And what they were doing with the

00:27:49.000 --> 00:27:53.000
DDT, is that they were killing the
natural predator of the wasp.

00:27:53.000 --> 00:27:57.000
And the caterpillars themselves,
while they were in the cocoon, were

00:27:57.000 --> 00:28:02.000
actually protected from the DDT.
So the more they put on,

00:28:02.000 --> 00:28:07.000
the more they killed the wasp,
and the caterpillars were released

00:28:07.000 --> 00:28:13.000
from this controlling predation,
and they had huge outbreaks. So,

00:28:13.000 --> 00:28:18.000
it's another example of in nature
it's really hard,

00:28:18.000 --> 00:28:23.000
you can't see what's controlling
what until you disrupt it.

00:28:23.000 --> 00:28:28.000
You have to experiment either
inadvertently or on purpose because

00:28:28.000 --> 00:28:34.000
everything is dynamic
and turning over.

00:28:34.000 --> 00:28:40.000
But it looks relatively stable.
And that's why this is so hard.

00:28:40.000 --> 00:28:46.000
And this is one of my favorite
examples of this,

00:28:46.000 --> 00:28:52.000
because it brings together a lot of
concepts that we've been talking

00:28:52.000 --> 00:28:59.000
about, is predation shapes
community structure.

00:28:59.000 --> 00:29:12.000
And this is another example of

00:29:12.000 --> 00:29:22.000
introduced species.
And this is St. John's Wort,

00:29:22.000 --> 00:29:32.000
which was introduced at California
from Europe.

00:29:32.000 --> 00:29:44.000
And, it, so I'm going to draw a
couple of habitats here.

00:29:44.000 --> 00:29:56.000
This is a forest, and this is a
meadow. So this is grass,

00:29:56.000 --> 00:30:06.000
OK, this is trees.
And these are St.

00:30:06.000 --> 00:30:14.000
John's Wort. So, it could grow
equally well in the meadow and in

00:30:14.000 --> 00:30:23.000
the forest. And it was getting out
of control so they introduced a

00:30:23.000 --> 00:30:31.000
beetle from Europe that feeds on St.
John's Wort to try to bring it in to

00:30:31.000 --> 00:30:41.000
under control.
And what they found was that the

00:30:41.000 --> 00:30:51.000
beetle, because the beetle's
preferred habitat was the meadow

00:30:51.000 --> 00:31:01.000
that St. John's Wort persisted in
the forests but was eliminated

00:31:01.000 --> 00:31:08.000
from the meadow.
Now, because the beetle prefers the

00:31:08.000 --> 00:31:13.000
sunny habitat of the meadow,
so if you were an ecologist and you

00:31:13.000 --> 00:31:19.000
didn't know that this beetle had
been introduced,

00:31:19.000 --> 00:31:24.000
you just walked into this state,
you knew nothing about the history,

00:31:24.000 --> 00:31:29.000
you wanted to study the ecological
niche of St. John's Wort,

00:31:29.000 --> 00:31:35.000
you would say, well, I only find it
in the forest.

00:31:35.000 --> 00:31:40.000
It must like cooler,
wetter environments because you

00:31:40.000 --> 00:31:46.000
wouldn't really know that it was
being controlled by the presence of

00:31:46.000 --> 00:31:52.000
this beetle. So, this
is a perfect example.

00:31:52.000 --> 00:32:03.000
If we draw the niche or two
dimensions of the ecological niche

00:32:03.000 --> 00:32:15.000
of St. John's Wort,
and we say that just on these two

00:32:15.000 --> 00:32:27.000
dimensions that this is the
fundamental niche on the moisture

00:32:27.000 --> 00:32:36.000
light gradient,
in the presence of this beetle,

00:32:36.000 --> 00:32:42.000
the realized niche is only this low
light, high moisture environment

00:32:42.000 --> 00:32:48.000
that you find in the forest.
OK, so in other words, to really

00:32:48.000 --> 00:32:54.000
understand what's regulating the
ecology of a particular organism,

00:32:54.000 --> 00:33:00.000
you have to understand all of the
other organisms that it's

00:33:00.000 --> 00:33:06.000
interacting with,
and what their effect is on this.

00:33:06.000 --> 00:33:11.000
And again, that's why it's so

00:33:11.000 --> 00:33:16.000
impossible to do this without some
form of experiment,

00:33:16.000 --> 00:33:21.000
either manipulative experiments like
I described, or experiments done in

00:33:21.000 --> 00:33:25.000
a lab, or inadvertent experiments by
introducing species.

00:33:25.000 --> 00:33:30.000
OK, now let's talk about a couple
of other really classic experiments

00:33:30.000 --> 00:33:35.000
that have been done.
And these are experiments that have

00:33:35.000 --> 00:33:40.000
illustrated the concept of keystone
predator. There are some predators

00:33:40.000 --> 00:33:45.000
and ecosystems that are what are
called keystones.

00:33:45.000 --> 00:33:50.000
And that is if you remove them,
the entire structure of the

00:33:50.000 --> 00:33:55.000
community changes.
There are some that if you move

00:33:55.000 --> 00:34:00.000
them, it doesn't have a dramatic
effect, but there are certain ones

00:34:00.000 --> 00:34:06.000
that are keystone predators
that it does.

00:34:06.000 --> 00:34:12.000
And these, of course,
are species that conservation

00:34:12.000 --> 00:34:19.000
biologists want to first identify,
and second conserve above others

00:34:19.000 --> 00:34:26.000
because there is a cascade of
effects if something happens to them.

00:34:26.000 --> 00:34:33.000
A classic example of this was a
study by Robert Payne many years ago

00:34:33.000 --> 00:34:41.000
in the inner tidal community.
I'm not going to go into the details

00:34:41.000 --> 00:34:51.000
of that, but the rocky inner tidal
community is made up of the starfish,

00:34:51.000 --> 00:35:01.000
which is called pisaster,
one of the top predators.

00:35:01.000 --> 00:35:09.000
And there are also limpets,
chitins, if you grew up in

00:35:09.000 --> 00:35:17.000
California you know probably what
these are, mussels.

00:35:17.000 --> 00:35:25.000
These are invertebrates-like
barnacles that stick to the ground,

00:35:25.000 --> 00:35:33.000
or stick to the rocks, and also
algae that stick to the rocks.

00:35:33.000 --> 00:35:38.000
And Payne hypothesized that the
predator was maintaining this

00:35:38.000 --> 00:35:43.000
diversity. And the way to test that
hypothesis was to put a cage over

00:35:43.000 --> 00:35:49.000
everything and eliminate the
predator from certain areas.

00:35:49.000 --> 00:35:54.000
At what he showed was that that's
what that ecosystem looks like if

00:35:54.000 --> 00:36:00.000
you eliminate the predator.
You can see here, here's the algae.

00:36:00.000 --> 00:36:05.000
Here are some articles.
This is a new textbook,

00:36:05.000 --> 00:36:10.000
see if you get the full story there,
but there's a lot of diversity of

00:36:10.000 --> 00:36:15.000
the small barnacle-like
invertebrates.

00:36:15.000 --> 00:36:20.000
Then you eliminate the predator,
and the mussels just completely take

00:36:20.000 --> 00:36:25.000
over. And this is preemptive
competition. They compete with

00:36:25.000 --> 00:36:30.000
everything else for space and
nothing else can survive there.

00:36:30.000 --> 00:36:36.000
Another example of a keystone
predator is the sea otter,

00:36:36.000 --> 00:36:42.000
which keeps the sea urchins in check
in the bottom of the substrate,

00:36:42.000 --> 00:36:49.000
and if the sea otter is not there
the sea urchins takeover and they

00:36:49.000 --> 00:36:55.000
exclude the kelp,
the entire kelp forests and all the

00:36:55.000 --> 00:37:02.000
fishes that lives in the kelp
forests, and all of the diversity of

00:37:02.000 --> 00:37:08.000
the ecosystem relies on the sea
otter's ability to keep the sea

00:37:08.000 --> 00:37:15.000
urchin population in check.
OK, so some of the best evidence for

00:37:15.000 --> 00:37:22.000
predation as an evolutionary agent,
or something that's driving the

00:37:22.000 --> 00:37:30.000
natural selection of organisms,
are these defenses that have evolved

00:37:30.000 --> 00:37:36.000
to avoid predation.
In other words,

00:37:36.000 --> 00:37:41.000
if you're constantly under attack,
your fitness will be increased by

00:37:41.000 --> 00:37:46.000
features that reduce your
susceptibility to predation.

00:37:46.000 --> 00:37:52.000
So in this case, there are a lot of
experiments. I'm going to show you

00:37:52.000 --> 00:37:57.000
a few, but a picture's worth a
thousand words here.

00:37:57.000 --> 00:38:03.000
I'll show you some examples.
Cryptic coloration is when a prey

00:38:03.000 --> 00:38:09.000
organism has color features that
make it blend in to the environment.

00:38:09.000 --> 00:38:15.000
So here's a very famous example
that was actually in another

00:38:15.000 --> 00:38:21.000
inadvertent experiment.
This is a moth that comes in two

00:38:21.000 --> 00:38:27.000
forms. This is called the melanic
form, which is dark black or gray,

00:38:27.000 --> 00:38:33.000
and this is the other form which is
much lighter.

00:38:33.000 --> 00:38:37.000
And here it is on a birch tree.
You can see that this one blends it

00:38:37.000 --> 00:38:42.000
beautifully, whereas this one,
if I were a predator looking for the

00:38:42.000 --> 00:38:47.000
moth, I would see this but I
wouldn't see that.

00:38:47.000 --> 00:38:52.000
Here's the same two moths on
another tree with darker bark

00:38:52.000 --> 00:38:56.000
showing that in this case,
this one would be more fit in that

00:38:56.000 --> 00:39:01.000
one would be less fit.
And there's a very famous study

00:39:01.000 --> 00:39:06.000
that I don't have time to go into,
but it's a textbook, that showed

00:39:06.000 --> 00:39:11.000
experimentally the relative fitness
between these two forms,

00:39:11.000 --> 00:39:16.000
depending on the color of the tree
trunks.

00:39:16.000 --> 00:39:21.000
And this whole example is called
industrial melanism because the

00:39:21.000 --> 00:39:26.000
reason this was noticed was that in
areas of high industrialization the

00:39:26.000 --> 00:39:32.000
tree trunks are darker colored
because of the air pollution.

00:39:32.000 --> 00:39:36.000
This is back in England back in the
days when there is a lot more air

00:39:36.000 --> 00:39:41.000
pollution. So,
they were able to show a shift in

00:39:41.000 --> 00:39:46.000
the frequency of these two forms as
a function of the amount of

00:39:46.000 --> 00:39:51.000
pollution and environment because
their susceptibility to predation

00:39:51.000 --> 00:39:55.000
was reduced if this form dominated.
That study is actually rather

00:39:55.000 --> 00:40:00.000
controversial now,
so I won't teach you the details.

00:40:00.000 --> 00:40:06.000
But you get the point.
But these moths exist in these two

00:40:06.000 --> 00:40:12.000
forms. Here's another example
that's really convoluted that's in

00:40:12.000 --> 00:40:18.000
your textbook.
So I'm not going to write it on the

00:40:18.000 --> 00:40:24.000
board. You can read about it there.
But it's an example of what's

00:40:24.000 --> 00:40:30.000
called the evolutionary arms race.
And it has to do with Cottonwood

00:40:30.000 --> 00:40:36.000
trees. And Cottonwood trees produce
a defense compound that the name of

00:40:36.000 --> 00:40:43.000
which is on the next slide:
salicorten.

00:40:43.000 --> 00:40:50.000
It doesn't matter what it's
called, it's a toxic compound that

00:40:50.000 --> 00:40:57.000
makes the tree distasteful to
predator. You don't think of

00:40:57.000 --> 00:41:05.000
predators of trees.
The beaver is a tree predator.

00:41:05.000 --> 00:41:10.000
It chops it down.
So when a beaver chops it down,

00:41:10.000 --> 00:41:15.000
a Cottonwood tree, the Cottonwood
tree sprouts new sprouts.

00:41:15.000 --> 00:41:21.000
And the resprouts have much higher
concentrations of this toxic

00:41:21.000 --> 00:41:26.000
compound than the parent tree had.
In other words, the tree has a

00:41:26.000 --> 00:41:32.000
mechanism. And I'm sure we don't
understand that yet,

00:41:32.000 --> 00:41:37.000
but someday we'll understand the
genetic underpinnings of this,

00:41:37.000 --> 00:41:43.000
the molecular biology of beaver
defenses.

00:41:43.000 --> 00:41:47.000
But if it's been felled by a beaver,
it increases the production of this

00:41:47.000 --> 00:41:52.000
toxin in the shoots that come out
saying, OK, fool me once,

00:41:52.000 --> 00:41:56.000
but you're not getting to get me the
next time. It means there's beavers

00:41:56.000 --> 00:42:01.000
around. But the interesting thing
is that these shoots are much more

00:42:01.000 --> 00:42:06.000
susceptible to grazing
by a leaf beetle.

00:42:06.000 --> 00:42:10.000
In other words,
this increased toxin,

00:42:10.000 --> 00:42:15.000
the shoots that have the increased
toxin, are actually grazed more than

00:42:15.000 --> 00:42:19.000
the parent tree by this leaf beetle.
So scientists went in and said, you

00:42:19.000 --> 00:42:24.000
know, what's going on here?
This is weird. Why make a defense

00:42:24.000 --> 00:42:29.000
that makes you more vulnerable to a
different predator?

00:42:29.000 --> 00:42:33.000
And what they showed by experiment
was that these leaf beetles were

00:42:33.000 --> 00:42:38.000
using that toxin as a defense
against the ants that

00:42:38.000 --> 00:42:43.000
want to eat them.
So, they were less susceptible to

00:42:43.000 --> 00:42:49.000
predation by ants because they had
taken in the toxin from the shoots.

00:42:49.000 --> 00:42:55.000
So, it's called the evolutionary
arms race between predator and prey.

00:42:55.000 --> 00:43:01.000
In these systems get very
complex.

00:43:01.000 --> 00:43:07.000
So here's the data that shows that,
that the control trees, trees that

00:43:07.000 --> 00:43:13.000
haven't been felled by a beaver
compared to trees that have been

00:43:13.000 --> 00:43:19.000
felled by a beaver,
and resprouted trees have a much

00:43:19.000 --> 00:43:25.000
higher concentration of this toxin.
And this is the larval survival

00:43:25.000 --> 00:43:31.000
time of these leaf beetles that
these are from the control trees

00:43:31.000 --> 00:43:37.000
versus the browsed trees in the
presence of the ants.

00:43:37.000 --> 00:43:43.000
OK, I'm going to skip that one.
That ones in your book, too, which

00:43:43.000 --> 00:43:50.000
has an experiment showing that
anti-predation mechanisms are

00:43:50.000 --> 00:43:57.000
induced by the presence of a
predator. So I would encourage you

00:43:57.000 --> 00:44:04.000
to look at this in a textbook,
this example.

00:44:04.000 --> 00:44:09.000
And then finally I'm just going to
go through a series of pictures that

00:44:09.000 --> 00:44:15.000
show all of the types of defenses
that have been evolved as

00:44:15.000 --> 00:44:20.000
anti-predation devices.
They are the obvious ones like

00:44:20.000 --> 00:44:26.000
cacti with spikes,
or porcupines with spikes,

00:44:26.000 --> 00:44:32.000
octopi with ink defense. This is a
caterpillar that has evolved to look

00:44:32.000 --> 00:44:38.000
like a snake, at least that's the
way it looks to us.

00:44:38.000 --> 00:44:42.000
I mean that's a hypothesis,
that the predation on this would be

00:44:42.000 --> 00:44:46.000
reduced because it looks like a
predator itself.

00:44:46.000 --> 00:44:50.000
These are two different ones
looking like a snake.

00:44:50.000 --> 00:44:54.000
And often, snakes have a bright
colored thing on their tail to draw

00:44:54.000 --> 00:44:58.000
attention to the tail.
If you're going to be attacked by a

00:44:58.000 --> 00:45:02.000
predator, you'd rather have your
tail attacked than your head.

00:45:02.000 --> 00:45:08.000
So, this is a common motif in nature.
And this is an insect.

00:45:08.000 --> 00:45:14.000
This is its head. And yet,
if you're a predator you'd probably

00:45:14.000 --> 00:45:20.000
think this was its head.
And again, whether that's been

00:45:20.000 --> 00:45:26.000
established by experiments,
I don't know. So these are just

00:45:26.000 --> 00:45:32.000
examples. Moths often have features
that look like eyes that what tends

00:45:32.000 --> 00:45:37.000
to ward off a predator.
This is an interesting story that is

00:45:37.000 --> 00:45:43.000
in your readings that shows that
there are just a few genes that

00:45:43.000 --> 00:45:48.000
control the phenotype of this
particular butterfly.

00:45:48.000 --> 00:45:53.000
I think it's a moth, between having
these spots and not having the spots.

00:45:53.000 --> 00:45:59.000
In the fall, when it's dry and it's
more selective advantage to look

00:45:59.000 --> 00:46:04.000
like a leaf, they look like this.
But at other times,

00:46:04.000 --> 00:46:08.000
they're visible anyway so their
selective advantage is to have these

00:46:08.000 --> 00:46:13.000
eye spots that make them look like
they have eyes.

00:46:13.000 --> 00:46:17.000
OK, I think it's time to quit,
so we'll pick this up next time,

00:46:17.000 --> 00:46:22.000
I promise you. Their wonderful
pictures of the creatures in the

00:46:22.000 --> 00:46:26.000
deep sea that are very evil looking
predators that fish with their

00:46:26.000 --> 00:46:29.000
luminescent light organs.