- Hello, my name's Lindsay Turnbull
and I teach biology at the University of Oxford.
In this video,
I want to zoom out, away from individual organisms
and into the systems that they both create and inhabit.
In other words, I want to talk about ecology.
That's the title of the final chapter of my book,
"Biology: The Whole Story."
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Ecology is the study of organisms in their environments,
and the environment consists
of both the physical environment like the temperature,
but also other species.
Now, ecologists often study populations.
That's a group of individuals
all belonging to the same species
that live in the same place.
And ecologists try to answer various kinds of questions
about those populations.
And some classic questions include things like,
why are population sizes so different for different species?
Some are large, some are small.
Why are some populations very stable,
while others seem to boom and burst?
And finally, a very important question,
why is it that populations of just one or two species
don't just take over the world?
Instead, we see this huge diversity of species
on our planet.
So let's consider now the state of populations.
If we want to know
whether a population is going to stay the same size
or get bigger or smaller,
then we need to stay focused on just two things,
the number of births and the number of deaths.
So let's say we're studying a population
and we know how many adults there are this year,
but we'd like to know
how many adults there are going to be next year.
Then the first thing we need to know
is how many of the existing adults are going to die
between this year and next year?
And then how many new adults
are going to be joining the population?
Now, new adults come from the offspring
of the existing adults.
It's the new adults are the number of young
that survive successfully to adulthood.
So it's the balance of the births and the deaths
that's going to matter.
So if the number of existing adults that die
is exactly the same as the number of new adults
that join the population,
then this population is going to be stable.
The number of adults next year is gonna be the same
as the number of adults this year.
But if those numbers are out of balance,
so the number of adults that die
is greater than the number that join,
then obviously the population's going to decline.
But if the number of adults that die
is smaller than the number that join,
then the population's going to grow.
So there's just two things we can learn from this.
The first is this balance between births and deaths
is crucial.
The second thing, if you think hard about it,
is for a population to persist through time,
all the parents need to do
is make sure that they replace themselves before they die.
And that means that each pair of parents
has got to produce two surviving offspring.
So just how easy is it for adults to replace themselves
before they die?
Well, it's easier for some animals than for others.
For something like a rabbit, which is famously prolific,
quite easy.
A single female rabbit
can give birth to up to 12 babies in a single litter
and can have multiple litters in a year.
So even if something has increased the death rate of adults,
like humans who shoot rabbits,
it's pretty hard to eliminate rabbits,
because they have a very high birth rate
and can compensate for all those extra deaths.
But at the other end of the scale,
we have something like the Albatross.
These beautiful huge seabirds
mostly live in the southern hemisphere.
Now they only have a single chick a year,
sometimes only one chick every two years.
And that's okay, 'cause they're very long lived adults.
But if something happens to increase the death rate
of albatross adults,
it's not gonna be easy for them
to compensate for those extra deaths
by producing lots of extra chicks.
They just can't do it.
They live in these very crowded colonies.
There's no extra space for them to nest,
and they can't lay more than one egg a year.
And that means it's very easy for us humans, for example,
to impact albatross populations.
When we fish for tuna,
we hang out these hooks
and they're baited with squid to catch the tuna
and the albatross see them and they fly down.
They try to take the squid, and they often die on the hooks.
And this slightly increased death rate
is causing albatross populations around the world
to decline.
Now, in the opening section,
I also talked about other species.
So each population affects other populations
in different ways.
So one of the classic ways, of course,
is that animals eat each other.
So we might expect that predator populations
can have quite dramatic impacts,
but actually the effect of predators
can be really far reaching
throughout the ecosystems that they inhabit.
And one of the ways we discovered that
is that we often persecute predators.
And one of the animals that we've persecuted
is this incredibly cute animal called the sea otter,
which lives on the West Coast of the USA
from Alaska all the way down to California.
And they were hunted heavily in the 19th century
for their fur.
Now, eventually this hunting was banned
and sea otter populations rebounded.
But alongside them, a whole ecosystem rebounded too.
Because this is a kelp forest.
It's made up of these enormous underwater algae,
and it shelters and provides home
for huge numbers of other species like fish and crabs.
And once otter numbers started to recover,
then kelp forests started to regrow too.
And why was that?
Well, it's because sea otters eat many different things.
But one of the things they eat are sea urchins.
And if sea urchins are not eaten by otters,
then their numbers increase very rapidly
and you can get huge populations of urchins
and they munch away at the bottom of the kelp
and the entire forest just floats off into the ocean.
So sea otters are sometimes known as keystone species.
And the reason they're called that
is they have disproportionate impacts.
So there's not that many sea otters
that they still have a huge impact on the ecosystems
that they inhabit.
Well, that's an example of a predator in action.
But all species have to stay focused on the competition.
You know, we live in a very competitive world,
all species do.
So we might ask ourselves,
how come there's room on the earth
for all the millions of species that inhabit it?
Well, let's look closely at a classic example
and see how that works.
So if you go down to the rocky shore anywhere in the UK,
you will find barnacles.
These are tiny little crustaceans
that stick themselves down to a rock,
and then they secrete a little pyramidal shell to hide in.
Now they live in what's called the tidal zone.
That's the part of the beach that gets covered by the water
for part of the day only.
And when the water covers the barnacles,
then they open the little shell
and out pops this little creature,
and it filter feeds,
scooping up all of the good bits in the water.
And when the tide recedes
and it's left high and dry,
then it shuts the shell up
and it's trying to survive and not get dried out.
Now, if we look closely on the rocky shore,
there isn't just one species of barnacle, amazingly.
There are at least two.
There's one that specialises on the upper shore
and one that specialises on the lower shore.
And they don't really look that different.
But the one on the upper shore
is better at surviving those periods of desiccation
when there's no water covering it.
The one on the lower shore
is better at taking advantage
of the extra feeding opportunities it gets
because it's covered by water more of the time.
And it's better at feeding quickly and growing faster.
So each barnacle species can outcompete the other
in some part of the rocky shore.
And that's why we have two species of barnacle and not one.
And we can apply that to the rest of the planet.
There are species specialising
on every kind of special kind of environment.
And we call that the ecological niche of a species,
the precise conditions that a species needs to thrive.
So we can't have a single species of barnacle
dominating the entire rocky shore
because you know, one barnacle can't do it all.
But there is one species on this planet right now
that does seem to be able to do it all.
And that's us, of course.
We're everywhere, living on every continent.
And how's that possible?
Well, we're not really constrained
by an ecological niche anymore.
We've been able to expand it, because of our big brains.
We've been able to make warm clothes
so that we can live in the Arctic.
We can make shelters so we can live in hot deserts.
We can access just about every type of food,
partly 'cause we've invented things like cooking
that make some foods that would've been indigestible to us,
digestible,
and we're having an extraordinary impact on the planet.
For example, something like 64%
of the mammal biomass on this earth
is just the livestock that we eat.
About 34% of it is us, the human biomass.
And the remaining bit
is the other wild mammals like the sea otter.
So they've barely got anything left.
And to feed all those livestock,
we've destroyed a lot of other habitats.
Chopping down rainforest to grow soybeans to feed them,
or catching fish in the ocean,
which are also often used to feed animals
that we want to eat.
And some of our impacts, of course, are inadvertent.
When we fish for tuna, we're also killing albatrosses.
It can feel at times indeed,
like we are living through a mass extinction.
We are changing the composition of the atmosphere
very rapidly,
and we are eliminating a lot of other species.
So what does that mean for us?
Well, it can certainly sometimes feel depressing.
I admit, I also feel sometimes quite depressed
about what humans are doing.
But we mustn't allow ourselves to do that.
The first thing we need to do
is arm ourselves with knowledge.
And if you've been watching this whole series,
I hope you feel a little bit better prepared
to understand the problems.
There's a lot of misinformation out there
and we need to fight that.
The second thing we need to understand is we can act,
even if we only feel that we can act locally.
In our schools or in our workplaces,
we can start to bring about the kind of changes that we need
and we can link up with other people around us
who are like-minded.
There's lots of great information out there
about what you can do as an individual
and as a group
to ensure that you have the least possible impact
on the planet and the other species on it.
And finally, let's just have a reminder
of why it's worth doing all of these things.
Our planet is covered with some truly incredible life,
and much of that life is still there.
Yes, we have lost species,
but there's lots of things that can still be saved.
Look at this incredible coral reef of thousands of species.
These things need us to act and change the way we live,
and we can all do it.
Well, I do hope you enjoyed that final video
because that is it.
"Biology: The Whole Story."
We've reached the end of the series.
I particularly hope
that this series has helped to persuade you
that biology is not boring.
It is the study of life on earth around us.
And surely there's nothing more fascinating than that.
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