Bergmann's rule and Allen's rule

Welcome, guys.

Welcome to another session
of Shomu's Biology.

And in this lecture,
we are majorly

focusing on all those
competitive exams

like NET, GATE, GRE and
all these different exams

for preparing biology.

And here, I am going
to talk a little bit

about ecological rules.

There are different
types of rules

in ecology, rules coming
from different scientists,

different ecologists
all the time.

Many rules are there.

Among all of them, I encourage
you to actually understand

three major rules.

One is, and the
most important one,

is called the Gause's principle.

Or it's also termed as
competition exclusion principle

or competitive
exclusion principle.

Now, this competition exclusion
principle is the most important.

And I have a separate video to
talk about this particular rule.

So I encourage you to go
there and watch the video.

In my channel.

You will find a video among
ecology playlist about this.

I'm not going to talk about that
exclusion competitive exclusion

principle here.

Instead, there are
other two rules.

So let me write here that
first major rule that I

encourage you to know is
the competitive or Gause's

principle.

Or it's called competitive
exclusion principle.

Second one is Allen's rule.

And third one is
Bergmann's rule.

I think you probably heard
this name, Bergmann's rule.

This is very, very famous.

So I encourage you to understand
this by looking the other video.

I have a separate
video dedicated

to explain about
that particular rule.

But still, I'm talking about
that rule in a very nutshell

here.

Competitive exclusion
principle is

suggesting that in a particular
niche, ecological niche,

no two species can
coexist together.

If they have same food
source, if they have same,

I mean, the environment
to live, two complete--

I mean, two species cannot live
together without having any

competition.

That's the competitive
exclusion principle rules.

And it's also telling us that
complete competition is not

possible because if there is
any competition between two

species for their food source,
for their environmental source,

they will fight with each other.

And that one which is having
advantageous effect will win,

and they will be
selected naturally.

And the other one will
lose and will be terminated

from that particular niche.

That is the basic idea.

And that particular
idea is actually

proved using several
experiments using

paramecium species, two
different paramecium species,

actually.

Second one is the Allen's rule.

And this Allen's rule
and Bergmann's rule,

they are kind of
similar because they

are talking about the size--

I mean, volume is to
surface area ratio.

They talk about
volume is to surface

area ratio, about the
different type of animals.

that are living in
either Arctic region

or in the equatorial region.

Now, if you look at here,
these two regions, that Arctic

or polar, whatever, or
equatorial, so different animals

are present in
both these regions.

Now, according to Allen's
rule that the animals that

are present-- majorly,
they focus on mammals.

The animals that are
present in Arctic regions

tend to have smaller ears,
tail, and foot compared

to the equatorial animals.

And also similar case for birds.

They tend to have shorter
wings, thinner wings in Arctic

than the equatorial regions.

So let me write according
to Allen's rule--

ear, the tail, wing,
short, and this

is long for animals and birds.

Now, why if we are living
in the Arctic region

and if we are having larger tail
or ears and all these regions?

So these regions tend to more
exposure to the environment,

because we actually have all
those things in the cooler

parts of our body.

These are the cooler parts--

always ear, tail, and the foot.

All these things
are cooler parts.

And they are present
in the cooler part

and near to the cooler
part of our body.

So in this case, if
these regions are larger,

if the surface area is more
in this particular areas,

we will lose more heat.

And majorly, I forgot to
mention the important point.

This rule applicable only
to the endothermal animals.

Endothermal animal means they
are having a body temperature,

which is really, really hot.

For example, us.

We are warm blooded animals,
body temperature is hot.

Core temperature is high than
the environmental temperature.

In those cases, we have
these type of scenarios.

So for that reason,
if we have our surface

area larger exposure
to the colder climate,

then we will be--

it will be very hard for us to
maintain the body temperature.

To minimize that effect,
usually, your tail and wing

are becoming shorter in this
Arctic climate or very cooler

climate.

On the other hand, in
equatorial climate,

we don't require that because
the temperature outside

is kind of balanced already.

So we have a long ear,
tail, and all these parts.

And in that case,
also they need to be

longer because,
in that case also,

we need to release
the heat pretty early.

Otherwise, we can't release it.

So we require higher
surface area here,

lower surface area there.

Now, the second-- and the third
one is the Bergmann's rule.

Bergmann's rule is also about
this temperature and surface

area is to volume
ratio of animals.

But it is suggesting us
that the animals that

are present in the Arctic region
are having the overall size,

the complete size to be
more than the animal present

in the equatorial region.

For example, mammals.

If

You take polar
bear, the polar bear

tends to have a very huge
body than the bears that

are present in equatorial
region, like brown bear.

Brown bears are pretty much
smaller than the polar bears.

Polar bears are giants, huge.

The reason is,
again, for the same

because once you talk about the
polar bear, they are larger.

The weight is huge.

In that aspect,
their body is huge.

The surface area as to
volume ratio goes down.

If their body becomes less, and
if their size becomes smaller,

in that case, using
the same surface area,

it will be more for the volume
to surface area ratio-- surface

area as to volume ratio.

Now, in case of--
normally, what do we know?

Surface area by volume.

This is the formula.

So suppose, surface area
for the polar bear is more.

Surface area for, say,
the polar bear here, let's

say the brown bear here.

So surface area is more
for the polar bear.

Let's say-- let me write
15 for general calculation.

And the volume let's
say here is more.

Let's say it's 30.

In this case of brown bear,
the surface area is 10.

Not huge difference
in that aspect

because the surface is also
filled with those materials--

I mean foreign materials.

And the volume here
is much smaller.

You can see the volume
is huge difference.

The size is huge difference.

So ultimately, we get a
surface area to volume ratio

is 2 is to 1.

On the other hand,
we get 0.5 is to--

I mean 1 is to 2.

I guess 1 is to 2

So you can see the
surface area as

to volume ratio is much more
minimized if we have more

size in the colder climate.

That is the reason,
if I write here,

according to Bergmann's rule,
for polar bear, large body.

The size is huge.

In the equatorial region,
brown bear, smaller, smaller

compared to that of--

I mean, polar bear.

So these are the different rules
that are present in ecology.

And these three rules I find
very interesting as well as very

important for all those exams.

So be prepared with them.

Thank you.