So...
in your book in Chapter 17
the importance of wolves to the Yellowstone ecosystem
is the main topic.
And we have talked already about the connections between living things
and their environment;
and how there are different
types of interactions.
We also found out that wolves fulfill
a very important role in the community:
they're a keystone species.
Which means that they have a really
big influence for their population size on the community structure;
and their presence or absence can really change that community structure.
Wolves occupy
a very important niche in the Yellowstone ecosystem.
And a niche simply refers to,
what is an organisms role in its environment?
What does it do?
Who does it interact with, and how?
What are its needs?
So, really, the needs and the...
interactions of an organism
in an ecosystem
describe this concept of a niche.
Basically, everything about how
it acts in that ecosystem.
If there is overlap of a niche,
a place where needs and roles overlap,
then we get our last type of biological interaction: competition.
Competition is going to take place
when two organisms,
two species,
or two members of the same species
are interacting in a way that indicates that they are competing for a resource.
So, for example, here we have a little parakeet
and a starling that are fighting over a french fry.
Now, hypothetically...
in the case of competition,
one competitor will usually manage to exclude the other competitor for that
--from that resource--
and we refer to this as competitive exclusion.
Organisms can compete for lots of things.
They can compete for space,
like these corals.
Um...
the corals are also competing for sunlight.
There is some algae sort of growing here in the corner of the picture;
and as that algae grows over the coral it takes up the sunlight and the coral
can't get it.
So organisms can compete for physical resources like:
space, sunlight, nutrients, water, things like that.
Organisms can compete for food.
The lions and hyenas are competing for food here.
You saw some competition in the "Battle At Krueger" video.
There was some very interesting competitive interactions taking place.
Organisms can compete for mates.
These are two male elephant seals,
uh, who are competing to become the "beach master."
And that is a real term that describes the male elephant seal that has control of
all the females on the beach.
Elephant seals have a harem mating system
where one male mates with the females, and, of course,
for that evolutionary fitness, for that reproductive success,
that is a very hotly contested position.
You can see they are battling pretty hard. They are bloody and fighting, uhm...
What's really interesting about the elephant seal situation is that you do
have a little bit of disruptive selection.
There are "sneaker males," as well, in that system.
But, there is very intense competition for mates.
When organisms compete
they can compete in different ways.
Some organisms compete by taking up, using up a resource.
And we refer to this as exploitation competition.
Now, this is different from the exploitation that we talked about earlier
when we talked about how parasites and predators exploit other organisms.
In the case of exploitation competition, you can also think of it as "scramble."
This squirrel is hoarding nuts.
He's gathered up nuts and he is sitting on them and he's com--com--com...
um, taking up that resource and keeping other organisms from getting it.
So exploitation competition can happen when an organism uses up a resource
and doesn't allow other organisms to access it.
Interference competition, on the other hand,
is when you have organisms that are physically competing, or interfering,
with one another for a resource.
This is sometimes referred to as "contest competition."
So, in this case you have a, uh...
a little ground squirrel and some starlings that are competing for nuts.
And, instead of--instead of the ground squirrel hogging all the nuts
and just setting them aside,
instead what we have is an actual, physical altercation,
a fight if you will, for that resource.
So, exploitation competition: using up the resources.
Interference competition: physically competing over them and--and
physically keeping other organisms from having them.
So those are two different strategies for competition.
And depending on the organism and the resource, you might see either
of those take place.
The coral example here, we have the algae is engaging
in exploitation competition by
covering up the coral and keeping it from getting light.
The elephant seals are engaging in interference competition
by physically battling one another
for the mates.
Okay...
When competition occurs
one of the things that we see
is that one competitor,
if they have the same exact needs,
will often out compete the other predator.
So here are two protists.
Um , Paramecium aurelia and Paramecium caudatum.
That, if grown in separate flasks,
in separate conditions,
we see almost the exact same population growth curves.
They grow in the same way.
If, however, we put them in the same flask
Paramecium aurelia ultimately out competes Paramecium caudatum
because two organisms cannot occupy the same niche simultaneously
and continuously.
This is known as competitive exclusion.
So, the parrot and the starling competing for a french fry,
if they lived in the exact same environment and only ate the same
food, over time what we would see is one competitor would be a superior
competitor; out compete the other one. and we would get competitive exclusion.
How organisms get around this is through resource partitioning.
For example:
this is a group of birds, warblers,
a closely related species,
that are engaging in resource partitioning.
They use different resources
to allow them
to effectively coexist.
So, some of the warblers use different parts of the tree.
The myrtle warbler, for example, is found in the mid-section, the lower mid-section
of the tree.
While the cape may warbler is found at the tops of the trees.
They eat different things.
Black throated warblers that live sort of near the tops are eating
small worms and grubs.
Where cape may warblers are actually uh, eating flying insects.
So we have different forms of competition
different types of resources being used here.
Different spaces, different food items...
And so these birds have engaged in resource partitioning
where they take advantage of different resources
so that they can still gain a foothold in the ecosystem.
One of the things we might see here though is that
some areas of this tree, or some types of insect prey may not be as desire--
as desirable as others.
So that when one resource is removed, or one competitor is removed
we might see changes.
And so competition really can influence distributions in time and space.
Here is an example from the Oregon Coast.
We have two different species that are living on the coastline here,
we have barnacles
and we have mussels.
And these two organisms both like to live in the inner tidal zone.
This is an area between the high and low tides that is partially covered by water
during a portion of the day .
And mussels tend to be very quickly growing.
They grow fast, they are a little bit bigger, and they can actually
-and you see this happening here-
they can crush and squeeze out barnacles.
They are engaging in some exploitation competition where they are physically
taking up a resource and keeping other organisms from getting it.
The problem that mussels have
is that...
while they are competitively excluding these barnacles
they are limited to the area
that is covered by water for much of the day.
They have a much lower tolerance for drying out than the barnacles do.
And so we see this very distinct,
what's called a zonation line,
that's separating the mussels and the barnacles
because barnacles can live in those higher, inner tidals
where there is less wave splash, but mussels can't survive.
So this is a good example of resource partitioning.
The mussels have excluded the barnacles from the--the wet zone down here
but he barnacles, because they can last a little bit longer out of water,
have been able to engage in resource partitioning and use this space up
in the high inner tidal.
What's kind of exciting
is that if mussels are removed in some way
then barnacles will spread
to fill the available space.
So perhaps we have a sea star predator that comes up here,
removes and eats the mussels,
barnacles will then spread to fill that available space
and this is known as "competitive release."
Basically if a superior competitor is removed
then the other competitor may take advantage of that better resource.
They don't have to resource partition anymore.
And so this the reason that sea stars are, themselves, considered a keystone
species on the Oregon Coast
and throughout the Pacific Northwest
because they wipe out big mussel populations and allow other kinds of
organisms to live in the inner tidal.
So, competition has a really big influence here,
but if our sea star comes along and removes that superior competitor,
it changes the community--
making the sea star another example of a keystone species.
And you can see that here in this actual picture of the, um, these sea stars
that come up to a certain level of the inner tidal
they've eaten a whole bunch of these mussels.
Remember from our example of co-evolution,
sea stars are great at eating shellfish because they pry open that shell
just a little bit
and push their stomachs inside out and inside that shell and--and dissolve those
nutrients in there and then [clicks tongue]
pull their stomachs back into their bodies.
So, here they have created this line of mussels and if you look below
the mussel line you can see all these different kinds of seaweed,
there's some other shells downs here,
some barnacles.
And they have really changed the community.
And we have different populations taking part in that community.
We have mussels,
we have sea stars,
we have barnacles,
we have algae,
all of those populations,
all the members of a species that are living together in a place
are interacting...
in this community.
And what we are going to see
is that competition
can occur between members of a community.
Like a lion and a crocodile.
And, in this case, what are a lion and a crocodile gonna compete for?
Well, they're certainly competing for food.
But, they may not be competing for all of the same things.
So here we have niche overlap that is just partial .
In this case, the lion and the crocodile
they're not competing for the same place to live;
the crocodile prefers an aquatic environment, the lion does not.
They're certainly not competing for mates.
However...
lions are going to have 100% niche overlap with other members of the same species.
And so competition tends to be much more intense between members
of the same species.
That's the difference between interspecific competition:
competition that takes place between members of a different species
and intraspecific competition that takes place between members of the same species.
And the real difference here is complete niche overlap.
If you're in the same species
you're competing for food,
for living space,
for mates,
because you have the exact same needs.
So one of the things that we see with competition that's really interesting
is that intraspecific competition tends to be the most intense competition
and is going to be much more intense,
in many cases,
than interspecific competition.
We are going to be focusing more next week on other kinds of dynamics that
influence the shape,
and size of these pop...
We are going to be looking in much more detail next week at other kinds
of interactions that influence the shape and size of these populations.
In the meantime, don't forget to do the "Battle At Krueger" online exercise for
your 5 activity points and to also participate in the discussion
forum for this week where you can ask and answer questions.
I will also be asking and answering questions
and that is going to help us keep up on these community interactions.