- [Instructor] Evolution and ecology
are really tied together,
so we're still on evolution here,
but when we study the
overall dynamics and effects
that organisms have within a
given area, that's ecology.
Okay, so the same principles apply
and now when we study ecology,
we look at various factors
to ultimately determine
the stability of that ecosystem.
Now, there's multiple ways in
which we can study ecology.
If we remember back from lecture one
where we studied the biological
organization of life,
it started with atoms,
and then to molecules, I'm not
gonna write the whole list,
but kept going down
until we got to the end
where we studied populations, communities,
ecosystems,
and then the biosphere.
So these are the highest
levels of organization of life
that we study,
so now we're at the tail end of our list
where we're looking at populations,
communities, and ecosystems
in terms of living systems
because in reality,
it's just a more complex organization.
So let's define these and
then we're gonna spend
all of lecture 18, today and Thursday,
talking about what population ecology is,
why it's important, why you study it,
'cause in reality, the main
purpose for studying these
is to understand whether or not
an ecosystem is thriving or failing.
Now, if you haven't learned our dependence
upon the stability of ecosystems yet,
you will definitely get that
here at the tail end, why?
Well, as we've talked
about, we're not autotrophs,
and the law of entropy is always in play,
which means that energy
is constantly being lost,
which is where our dependence
upon the sun comes into play.
Without this influx of energy,
you and I wouldn't be here,
so the food which we eat
and the ecosystems that they are part of
are crucial for your and my survival,
which is why studying ecology
and understanding its role
is extremely important,
because ultimately, as consumers,
we need those autotrophs, we
need those photosynthesizers
to survive and to do well.
Well, you can't just have
photosynthesizers in an ecosystem,
there needs to be a system
of constant recycling and things,
and this is where
decomposers come into play
and play their respective roles.
So as we start talking about ecology,
you're gonna see me throwing
various plants, animals, fungi,
the various organisms
that we've learned about
into these various groups
and look at their ecological
role and how vital they are,
and this is why we're
concerned about climate change
and things of that sort
is because of the stability
can be very easily disrupted
of these ecosystems.
So let's define these, what they are.
Population, let's recap.
A population is a group
of the same species
occupying the same geographical area.
That doesn't mean that's the
end-all of all of that species.
For example, there can be
multiple populations of a species
spread out throughout the world.
Obviously, the more
spread out a species is,
the greater the chances
they have of survival,
which is why humans are gonna
be around for quite a while.
But other species aren't so lucky.
Some species have very
restricted populations
because they cannot survive just anywhere,
they can only survive where
the temperature is right
and the precipitation is right,
and they have the right dynamics
as far as the ecosystem is concerned.
And when these organisms have
a change in their environment,
they very easily can go extinct,
and that will be the last concept we cover
in this lecture on Thursday
is how do we predict extinction
and what can we do about it?
What are the factors that
ultimately contribute
to the extinction of a species
and what are the ramifications
of the extinction of that species?
Community, when we look at a community,
we don't just study one species at a time,
we look at all of the species
in that given area at one time,
which is why it's the
next level of complexity
in studying biology
'cause it's obviously much
more complex to look at
all of the living
components of an environment
and how they interact with one another,
but that'll be for lecture 19.
And then ecosystems,
this is where we not only
look at the living components,
which is all life in an area,
but also the non-living components,
such as nutrient cycling,
water cycling, energy flow,
things that are vital for the
stability of an ecosystem,
but we look at everything,
we look at all components,
living and non-living
of a particular area,
and so that's why ecosystems, again,
are the next level of complexity.
Now, we're not going to spend
a considerable amount of time
on the biosphere because
this level of study
is the whole Earth,
looking at how all terrestrial
and aquatic ecosystems
interact with one another,
which is a huge endeavor,
to look at tidal currents
and energy distribution
and all of these factors
that play a key role,
which is why the better our science is,
the better our models of prediction
of what might happen and what will happen,
related to climate
change and other factors
that are important for us to understand.
So, population, community, ecosystem,
these are the three last
levels of complexity
that we study in any biological system.
Now, let's start with population ecology.
What is it that scientists study
when they study an individual species?
The ultimate goal of studying the species
is pretty much to determine
whether the species is thriving
or whether it's on the decline, okay?
And so we look at reproductive rates,
we look at population distribution,
we look at various factors
to ultimately give us an assessment.
It's basically a simplified version
to help us understand what's
happening to the species
in that environment, and
it tells us quite a bit.
Especially just looking
at the distribution
of the species in the environment
tells us quite a bit about the conditions
of that environment,
so let's look at the three
types of distributions
and then I'll show you a video
which illustrates one of these very well.
The first one is a random distribution.
Now, the picture is showing a lichen,
you remember, a fungi
and an algae together.
Random distributions
are typically observed
when there is an abundance of resources.
Now, resources isn't just food,
because remember, the lichens,
they could get food anywhere
as long as there's sunlight,
the algae can photosynthesize
and produce food for the fungus,
and so it doesn't matter
where they sit on the rock
or where they are in that particular area,
there's food everywhere because
there's sunlight everywhere.
Also, there's plenty of space,
so they're not restricted
to one area or another,
which is why their distribution is random.
So if we see a random distribution
with no pattern in it,
that usually tells us
that there's an abundance of resources.
A uniform distribution is the opposite.
Ultimately, this is because
of competition for resources.
Space is a resource as well.
Penguins, as shown here, have a,
yes, they're kinda clumped together,
but they also have that
uniform distribution.
You'll find this even with plants.
Plants get too close to one another,
they start competing over resources,
space for the roots,
food, nutrients, water,
and the light.
So you'll find that when a species tends
to start spreading out and
have this uniform distribution,
there's usually some competition
over a vital resource,
be it space, food, water, and the like.
It can also be a territorial thing
within the animal kingdom.
Other kingdoms without that
neurophysiological response
don't have a territory issue, so to speak,
but animals typically do,
so it might not be necessarily a resource,
but it could be a territorial,
which in a way, is still space issue,
but it's not that they're
running out of space,
it's just part of our nature.
Now, the clumped distribution
has a wide variety to it,
so this is the one
where you're gonna have to
pay particular attention
where there's a lot more
than just these others.
Now, clumped distribution
you typically find
when the species is localized
around the nutrients,
like an oasis.
So in an oasis, where the water is found,
you're going to find an abundance of life
because that's where the resources are at.
So when you get that clumped distribution,
that's because that's
where the resources are at.
Another thing, especially
for the animal kingdom,
and it occurs for the
plant kingdom as well,
but the closer you are to one another,
the more reproductive success you have.
So when you're close with
those of your species,
you have a greater chance
of reproductive success,
so that's another reason
for a clumped distribution.
Now, animals typically
travel in packs or herds
or murders, like with crows.
I don't know how they came
up with a murder of crows,
I don't know, but these various
groups have an advantage.
If you're typically the prey,
they have the advantage of
the protection of the group,
protection for the young and
protection for each other.
So animals that are typically vegetarians
and not carnivores or whatnot,
they ultimately protect their
young from the predators
that would normally get them.
Now, on the other hand,
predators, when they travel in groups,
have a greater chance of getting prey,
so it works both ways.
Prey have a better chance of
surviving in large groups,
predators have a better
chance of getting food
in large groups as well.
The next concept that scientists look at
for population ecology
is to study the dynamics
of how the population size is changing.
Basically, is it staying the same,
is it increasing, or is it decreasing?
Because when we look at the
survivability of the population,
then populations that are on the decline,
then we need to look at, well,
what is causing that decline?
So the first thing that we study
is not only just assessing
where they're at,
but where they're going.
Now, there are multiple factors
that can influence the rate
at which a population can grow.
The main ways in which a
population primarily grows
is the birthrate, obviously.
In order to propagate a species,
you must have reproductive success.
Now, in a species where
they're distributed
over numerous areas,
you can also have the population
increase by immigration,
where individuals from a
different population migrate in
and will contribute to the
population size as a whole,
but that doesn't influence
a population as dramatically
as the factors of the birthrate.
So primarily, the growth of a population
is primarily affected by the birthrate.
Now, we're gonna look at
what aspects of the species
allow them to grow rapidly, grow slowly.
There are certain
parameters that, over time,
if these change, and this
is about evolution as well,
species that tend to
have different dynamics
have different birthrates
because of how many offspring they have
and how often they can reproduce
and all of these factors
that we're gonna go into a little bit,
and that's really where I'm gonna focus in
most of the questions
is how changes in the number of offspring
they have per reproductive cycle
influences their population growth rate.
Does it increase it? Does it decrease it?
So it's fairly simplistic,
but we're gonna look at all these factors.
Now obviously, we also look at the factors
that take away from the
population's overall growth rate,
and that is death,
the primary reason in why a
population ultimately declines.
Now, we're also gonna
show a little bit later on
what are some of the things that limit
how fast the population can grow
as well as factor into how
much death is in a population,
and a lot of that comes down
to resources in the area,
predation, and other types of things.
Emigration is where individuals
move out of the population,
and that also subtracts from
the population as a whole,
but just like immigration, it
doesn't play as large a role
in the overall dynamic of how
fast the population grows,
but it does contribute to that.
So really, it comes down
to the birth to death ratio
in any species on how
fast they're growing.
If we look at the human species,
we see a huge dynamic across the world
in different countries
and different cultures
where in some areas, they're
growing quite rapidly.
In other areas, like here in the US,
we pretty much have what we
call replacement reproduction.
I think our reproductive rate is like .1%,
so we don't have hardly any growth at all
within the United States.
In China, where you might actually think
because of the number of individuals,
you would have a larger growth rate,
in fact, is on the decline,
and some other areas as well
have a declining population growth rate.
Now, this is not due necessarily
to space issues or things of that sort,
but rather more political
and other factors
that come into play.
So when we deal with people,
things start to get a little more messy,
so we're primarily gonna
deal with plants and animals
and not necessarily people
because we start making things
a little more messed up with
our (chuckles) psychology.
However, one of the big
concerns that we have,
and this is gonna be a different question
a little bit later on,
or related to a different
question later on,
is at what point can the human population
as a whole in the entire world,
at what point will we
not be sustainable, okay?
'Cause every environment limits
the number of individuals
that can reside within that area
based upon the availability
of space, food, water,
things of that sort.
So the big question that scientists have,
as well as others have, is
at what point will we reach
what's called the carrying capacity?
Now, humans have the ability to supersede
the natural carrying
capacity of any environment
primarily because of our ability to live
in godforsaken areas,
(chuckles) like a desert,
you know, here in Utah or something,
where in reality, the amount
of food that we produce locally
would only sustain about 10%
of the current population of Utah.
90% of the food is shipped
in from other places.
Now, due to modern
industry and technology,
we are able to live in areas that normally
would not be able to support
such a large population,
and so that's ultimately
why we have this huge spike
in growth in the overall
population of our species
because of the ability
to ship food elsewhere
and live in places that we
normally wouldn't be able
to have such a high
density of individuals.
Now, we've had our setbacks,
especially in Europe,
where we had the bubonic plague
and the pneumonic plague,
where we had a huge dip
due to the many, many
individuals that died.
Ultimately, because of
the Industrial Revolution,
our growth has spiked
and that's why it concerns
a lot of individuals
is because this can't go on indefinitely.
There is a point where we
will not have enough food
in order to be able to sustain
that large of a population.
Okay, so we're gonna talk
a little bit later on
about carrying capacity,
that will be the concept
that I'm gonna test you on,
but that's the concern
is every environment,
every area that houses a
population of any species
has a limitation of resources.
It's not unlimited, you
don't have unlimited space,
you don't have unlimited food production
and water availability
and things of that sort.
Now, let's talk about life strategies
or the ability for a species to reproduce.
What are the factors that ultimately
go into their reproductive success?
Now, remember we talked about
there was two main ways in
which organisms reproduce:
sexually and asexually.
Some can do both, some can do only one.
Typically, organisms
that reproduce asexually
grow much faster.
The reason for that is because
a lot of asexual reproduction
is done by smaller organisms,
single-celled organisms
and things of that sort.
Typically, if you're a
sexually reproducing species,
you tend to take a little bit longer
for your reproductive cycles.
Now that's not universally true,
there are some species
that reproduce asexually
that are slower in their
reproductive cycles
than species that reproduce sexually.
But on the whole, sexually
reproducing species
tend to have slower growth rates
versus individuals that clone themselves.
Lifespan also tends to have a correlation,
not necessarily a
causation, but a correlation
where longer-lived organisms
have a lot more time
in which they can be reproductively
active and successful,
in which case they tend to be slower
in their reproductive rates
than individuals that have
a very, very short lifespan.
That's one of the strategies
that they've developed
is that they don't live very long,
so they have to reproduce very rapidly
in order to sustain that
population and that species.
Now, this is a correlative
effect, not a causative effect
and the reason why I make that distinction
is because in the next few
scenarios that we go over,
there are evolutionary changes
within closely related
species that we've shown
that due to these slight changes
in when they reach sexual maturity,
how many offspring they have,
and things of that sort,
that actually increases
or decreases the rate
at which the population grows as a whole.
And so when we look at
those genetic changes,
ultimately, we can say,
"Oh, if this were to change,
"then this population would actually grow
"a little bit faster."
What it doesn't say is if all a sudden
the lifespan increases or
decreases of the species,
that's not going to cause the species
to reproduce more rapidly
or less rapidly, okay?
So although there's a correlative effect
between the lifespan,
there's not a causative
effect that all of a sudden,
you know, humans did not live
as long as we're living today,
that doesn't mean that we sped
up our reproductive cycles
or slowed them down for any reason,
it ultimately means we've had some changes
in our ability to sustain
life and things of that sort.
Same thing here,
just because an individual
reproduces sexually,
if all of a sudden, this rarely happens,
I can't even think of a
scenario, but if all of a sudden
they were to revert to
asexual reproduction,
it wouldn't necessarily mean
that the species would
start growing faster.
So there's not a correlation,
or a causation, I should say,
between changing their
mode of reproduction,
which really just doesn't happen.
Now, let's talk about some of
the things that are causative.
Age at which the species
reaches sexual maturity.
They've shown in closely
related species such as eagles
that when they reach sexual maturity
really has a dramatic effect
on the population growth rate.
For example, they show
that two species of eagles,
one reaches reproductive
age at like four years,
another one reaches
reproductive age at six years.
If you were to compare the
growth rate of these two species,
the one that reaches the sexual
maturity at four years old
ultimately, that species has 30 times
the rate of reproduction than the other.
They as a population essentially
reproduce 30 times faster
just because of that two-year difference
in their age of maturity.
So when we look at these factors,
these are the things that
we're concerned about
as far as how fast the
population will grow.
You'll see how all of this relates
to the survivability of a species
and their possible extinction,
which is what we're
primarily concerned about.
Now, when and how often it reproduces.
Some species only reproduce
once in their entire lifetime,
and you know, they reproduce
and then they die shortly thereafter.
Other species have a small window
in which they can reproduce,
and others have a huge window
in which they can reproduce.
So obviously, the more time a species has
in their reproductive cycle,
the more rapidly the species
will grow as a whole.
The less time they have
for reproductive cycles,
the slower they're going to grow.
Number and size of offspring,
how long does it take for the organisms
to go through a reproductive cycle?
For example, with people,
it's about nine months.
With elephants, it's over
a year, poor elephants.
Once they get pregnant,
before the elephant is ready to be born,
it takes over a year for
them to have their offspring.
And then the number of offspring.
Mice, I've seen one mouse
drop as many as 11 pups
(chuckles) in one reproductive cycle.
Mice ovulate every three days too,
so they have sex and they
get pregnant, essentially,
and that plays a huge role
as far as how fast these
organisms can grow.
Now let's look at the death aspect of it.
Ultimately, every area has
that carrying capacity,
those factors which limit how
much a population can grow.
So we look first at what
the reproductive strategy
of the population is
and how fast they grow
based upon the parameters
we just talked about,
and then we look at what factors
are keeping the population
size down to a certain point.
Well, there's two mechanisms in play
in any given environment.
We have what we call
density-dependent factors
and density-independent factors,
and in fact, we've
already gone over these.
What are they?
They're the biotic and abiotic components
of natural selection.
Basically, the living and
the non-living factors
that ultimately cause evolution
through natural selection,
but in this situation, when
we look at their effect,
we look at ultimately
what effect they have
on the population's density.
So the density-dependent factors
are ones in where if the density
of the population is small,
then these factors are also
small in their influence,
but the larger a population becomes,
the more these factors play a role
in keeping the population size down.
So as one increases, so does the other.
As one decreases, as far
as the population growth,
so does the other.
Now, what were the factors
that we talked about?
Predation, competition, parasitism,
these are the living
components of natural selection
that are also what we call
density-dependent factors.
For example, the more
individuals in an area,
the less resources per
individual there are
and therefore, competition
increases dramatically.
The fewer individuals there are,
the more resources
there are per individual
and so competition decreases.
So that's why it's called
a density-dependent factor,
it's because as the
population increases in size,
so does competition cause
an increase in death rate,
which keeps the population size down.
Parasitism, parasites spread faster
when the population is large.
So you saw that in the video
also with the Cordyceps fungi,
that when a population
gets extremely large,
they're very susceptible
to parasitic infection
and spreading of a disease,
whereas if the population is really small,
there's less likelihood of it spreading
and wiping out a species.
And then of course, predation,
the predator/prey relationship.
As the prey population goes up,
the predators have more to eat
and their population goes up.
As the prey population goes down,
then so does the predator population.
In fact, you'll find that
these two correlative events
are cyclical in nature.
You'll see one kind of
trailing right behind the other
as far as their population
growth rate and their death.
Now, this doesn't happen over the series
of a couple of months,
it usually happens over decades
where we see this increase and decrease,
we see these fluctuations
in the density of these populations.
But the correlation is still there,
the more prey there are,
the more predation there is,
the less prey there are,
the less predation there is.
So those are the
density-dependent factors.
Now, density-independent factors,
these are factors that will happen
no matter what the density
of the population is.
So the population, as it increases,
this doesn't influence the
density-independent factors.
What are we talking about?
We're talking about the
weather, the temperature,
the rainfall, any type
of natural disasters,
they're not caused by or influenced
by the density of the population.
So let's say one year, you
have 10 inches of rainfall,
and the next year, you
have two feet of rainfall,
and you saw that the
population had increased
from one year to the other by 10%,
that increase in the population
didn't make it rain more,
okay, so that's why it's called
density-independent factors.
- [Student] Isn't that
kind of the premise though
of global warming?
- [Instructor] On a global scale,
it has more to do with how the ecosystems
are influencing one another
rather than any one individual,
though there are situations
where in a local area,
especially because of us,
we can have differences
in inversion and pollution
and other types of things,
so whenever humans get
brought into the thing,
it just kinda screws it all up.
But when you look at like
just the normal circumstances
of the squirrels and the birds
and all that kind of stuff,
they're not going to directly influence,
but yes, you're right in the sense
that other factors are
influencing rainfall and weather
and other things that not only natural,
but manmade as well contributing,
so all of these things come into play.
But on an individual scale,
when we look at individual populations,
no one population is
really going to increase
or make it more likely that the
volcano's gonna erupt, okay?
So these natural disasters,
changes in temperature and
weather and things of that sort
ultimately can wipe out
90% of the population
whether you have 1000 individuals
or a million individuals.
It doesn't matter, it's going to destroy
or change the dynamics of the area
independent of what
the population size is.
So these are the factors
that ultimately cause
the death to increase,
competition increases death,
predation increases death,
parasites spreading increases death,
natural disasters increase death.
So ultimately, organisms find a balance
between their environment
and how fast they're growing
and how much death there is.
And like I said,
each environment has what
we call a carrying capacity
where there's a finite
number of resources,
food, space, water, and even energy.
I like to separate food and
energy because when I say food,
we usually think of organisms
consuming one another,
whether it's a vegetarian
or whether it's a carnivore
or whatnot, or decomposition,
and when I say energy,
I'm usually talking about
photosynthetic activity,
which is also a resource
for specific organisms,
and so that's why I say food and energy
is kind of two separate things,
but it just looks at how
they're getting that.
So what happens is if the
population grows rapidly enough,
it's eventually going to
reach that limit of resources
and this is what I was
saying in the beginning
about the human population.
We're in this exponential growth phase,
we're in this phase where we're
still growing very rapidly.
So the question becomes
when are we gonna hit
that carrying capacity?
And there's a lot of debate
on that, but once you hit it,
then what happens is due to
the competition for resources
and the limitation of space,
the death rate increases dramatically,
thus leveling off the population's ability
to grow beyond that and
it will dip down below.
So usually right here in
the middle of this wave
is where the carrying
capacity's actually at.
As you go below it, then more
resources become available,
the population will
start growing into that,
and they'll overshoot them
and so on and so forth.
So eventually, they stabilize
with the carrying capacity
of the environment.
Now, on a local level,
this is what plants and
animals are restricted to,
but since we humans have
the ability to supersede
the individual carrying
capacity of any one environment,
that's why the world is
our oyster, so to speak,
and we still have that question
when are we gonna reach that?
Now, (sighs) two main
strategies for any species exist
in terms of the general characteristics
as the population approaches
carrying capacity.
Some species tend to grow slowly
and reach carrying capacity
in almost an indiscernible manner.
Others grow so rapidly
that they overshoot the carrying capacity
and then they have huge
fluctuations in their population,
and when we analyze what
their overall growth rate is,
then we can see whether or
not the species are in danger
primarily by all of
these factors combined.
So let me give you the general outline.
There are pretty much two types
of life history patterns for organisms.
They're either opportunistic populations
in an ecological sense, or
equilibrium populations,
and these are the general characteristics
for these groups of organisms.
Now, this is not restricted
to any one kingdom or domain,
these are just how we classify
or separate two types of
organisms in any ecosystem
to be able to see what effect
they have on that ecosystem.
For example, opportunistic populations
are on the whole small organisms.
They mature very early
for sexual reproduction,
they tend to have very short lifespans,
and my favorite, I wish we had this,
limited parental care of offspring,
they don't take care of
their young as often,
as much as other organisms do.
Now, because of these factors,
they tend to exhibit what
we call exponential growth,
which is what I showed you before.
That's that nonlinear growth
where it starts growing very, very rapidly
and building exponentially upon itself.
Ultimately, this can't
happen indefinitely,
but you're dealing primarily
with small organisms,
rabbits, mice, bacteria,
these are the organisms that make use
of the resources available.
Now, before you think
that this is a bad thing,
it's actually a really good thing
because there are periods of time
where resources are so abundant
that they have to be used up very rapidly
and these are the organisms
that will take that opportunity,
which is why we call them opportunistic,
to get the nutrients as
fast as they possibly can.
Now, on the other side of the
coin, equilibrium populations,
these tend to bring stability
to an ecosystem, why?
Because they're pretty much the opposite.
They have much slower growth
called logistic growth, okay?
Logistic growth is one that happens,
it can happen, you know, somewhat rapidly
from a perspective of
comparing other species,
but on the whole, they grow very slowly.
We're talking about large animals here,
they have very few offspring
per reproductive cycle,
very few reproductive
cycles, long lifespan.
And so they're pretty much the opposite,
they take care of their young forever,
(clears throat) as it seems,
and so we belong to that.
And an ecosystem needs both
of these, they need the ones
that can use up the
resources very rapidly,
but they also need the stabilizers,
the ones that can actually
remain from year to year
and don't fluctuate too much
in their overall population size.
How do we bring all this together?
Well, the big question that we study
and ask with population ecology
is is the species going extinct?
So we have to look at a number of factors
to be able to determine
whether the species
will continue to thrive
in that environment
or whether they're on the decline
and will eventually go extinct, okay?
And why are we concerned about that?
Because as you'll learn
in the next lecture,
after spring break, when
a species goes extinct,
if that species is key for the
stability of the ecosystem,
then the ecosystem can collapse,
and this is the big
concern for climate change
is that if changing conditions
in these various ecosystems
change dramatically enough,
species may not be able to
survive the rapid changes
and if you wipe out certain key species,
you destroy the ecosystem,
and this is a very real
danger that we have
with these various regions,
which is why it's a big concern today.
Now, the three primary factors,
this doesn't mean other
things aren't considered,
but the three primary
factors that we look at
for the species and
whether or not we put them
on the Endangered Species
List are as follows.
The first one is the size
of their geographical range,
what do I mean by that?
Well, humans are not really
in any danger of going extinct
because we live everywhere, okay?
So we have so many different
places in which we can reside,
then we don't have a
small geographical range,
but there are some species
that reside in one forest,
in one part of the world and nowhere else.
That is the first warning sign
because they typically can't
survive in other conditions,
they have to be the right temperature,
it has to be the right dynamics, you know,
all of these factors have to come together
and if they're restricted to
a certain geographical range,
that's a danger, that's a warning sign
that they may go extinct.
Now, that by itself is not enough.
And then we look at another factor,
what we call the degree
of habitat tolerance.
This is their ability to evolve.
So how do we determine their
degree of habitat tolerance?
Well, we ultimately determine
it by their genetic variation.
The more genetically
diverse the species is,
the greater chances they have
of surviving changes in the conditions.
The less genetically diverse they are,
or the less genetic variation they have,
the more susceptible
they are to dying off,
and this is the case with
organisms like whales.
Because of our predation
of them over the years,
there is such little diversity
amongst some species of whales
that when their habitat
changes, 'cause it will,
as it always does over the years,
they're very likely to go extinct,
they will not have the ability
to adapt to major
changes in their habitat.
And then the third and final
comes down the size of the population,
and this is what we've been talking about
for pretty the whole lecture
is we look at reproductive
strategies, how fast they grow,
how much death there is,
ultimately comes down
to how many of the individuals are there?
If there are a few hundred,
that's a warning sign.
If there are a few million,
we're not too worried.
Now, sometimes we put
species on the watch list,
that's usually when they
have a couple of these,
but when they have all three,
where there's not very
many individuals left,
they only inhabit a particular
region in the world,
and they have very
little genetic diversity,
that's when we put them on
the Endangered Species List,
they're most likely gonna go extinct.
Now, sometimes it's our fault,
sometimes it's just the way things work.
If you look at the fossil
records on our planet,
99.9% of the species that have
lived on our planet are dead.
So change happens, species evolve,
and if they can't evolve,
they go extinct, they die off.
So what our concern is are we causing it?
We have to ask the question
are we causing the extinction
of these species and can
we do something about it?
And those are the questions
that we really should be asking
is what influence do we have on these?
Remember, each species has
its reproductive strategy,
some are exponential,
some are opportunistic,
but that's not the factor we look at
to determine whether or not
they're gonna go extinct.
Just because a species
only has one offspring
and grows once a year, or
has one offspring every year
and has this reproductive cycle
doesn't mean they're gonna go extinct,
because there's not really
a correlation there.
There is a correlation
between how many individuals there are,
their size of their habitat,
and ultimately their ability to adapt,
those are the things that
give us the warning signs
that they may not survive, okay?
Because each organism
has their strategies.
Now obviously, if they
have very few individuals,
but they grow very rapidly,
then we might say, "Oh,
they may come back."
So ultimately though,
these are the three factors
that we use to determine
whether or not they're at
risk of becoming extinct.
So yes, we do include
population growth rate
when analyzing the population,
but it's not one of
those things that we say,
"Oh, they grow really slowly,
"so they're in danger of dying off."
No, that's not the assessment.
