Module 1: Introduction to Ecology and Evolution

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The Levels of Organisation

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Today, we begin our second module which is ecological structures.
(Refer Slide Time: 00:19)

In this module, we are going to have three lectures,
1. The levels of organization,
2. Species abundance and composition, which is biodiversity and
3. A closer look at biodiversity.

(Refer Slide Time: 00:35)

So, let us begin with the levels of organization. We will start with the story. This is the
story of two watchmakers; written by Herbert Simon and it starts like this. There once
were two watchmakers named Hora and Tempus who manufactured very fine watches.
Both of them were very highly regarded and their phones in their workshops ran
frequently. New customers were constantly calling them.
However, Hora prospered while Tempus became poorer and poorer and finally, lost his
shop. What was the reason?
So, this is a story of two watchmakers.

(Refer Slide Time: 01:15)

One is called Hora and the second is called Tempus and both of them are very fine
watchmakers. Both of them are highly in demand and both of them have their workshops
in which the phones are ringing constantly because customers always want to know about
them. Now, in this case, Hora is the one that prospered or say he became rich, where is
Tempus is the one who became progressively poorer and poorer. So, this is a story through
which we will understand why organization is important.
Now, we move on. The watches, the men made consisted of about 1000 parts each. Tempus
had so constructed his assembly in such a way that if he had one partly assembled and had
to put it down to answer the phone say, it immediately fell to pieces and had to be
reassembled from the elements. The better the customers liked his watches, the more they
phoned him, the more difficult it became for him to find enough uninterrupted time to
finish a watch. Now, in both of these cases we have watches with 1000 elements or 1000
parts. Now, in the case of Tempus, he constructed a watch in a manner that you had to
bring all the parts together in one go to make the watch a functional watch.
So, all of these have to be together all the 1000 pieces have to come together at the same
time so that the watch becomes a functional watch. However, the better the watches he
made, with time as the quality of watches improved, the demand for the watches also
improved and when demand increases, the customers call him again and again, they phone
him in his workshop and Tempus has to leave his watch.

So, for instance if Tempus had prepared say 990 pieces he had put together, only 10 pieces
remained and then he gets a phone call. So, he has to leave these 990 pieces and go ahead
and attend the phone call. While he is attending the phone call, all of these pieces they just
break down and so they come up as different pieces which has to be assembled again. So,
this was the mode of operation of Tempus.
Now, because of this, whenever he got a phone call he was not able to complete his watch.
And so, his rate of production of watches deteriorated like anything and there would even
be days in which he would not be able to prepare a single watch. Because, you bring
together 500 elements, you get a phone call it comes down to 0; you then again start
making the watches, then again you get a phone call, again it goes down to 0 and so on.
(Refer Slide Time: 04:31)

Now, let us look at how Hora worked. The watches that Hora made were no less complex
than those of Tempus. But he had designed them so that he could put together sub
assemblies of about ten elements each. Ten of these sub assemblies again could be put
together into a larger sub assembly and a system of ten of the latter sub assemblies
constituted the whole watch.
Hence when Hora had to put down a partly assembled watch in order to answer the phone,
he lost only a small part of his work and he assembled his watches in only a fraction of the
man-hours it took Tempus. So, how did Hora prepare his watches? When the case of
Hora’s watches here again you have 1000 elements, but these 1000 elements work like

this. So, you have level 1, now in the case of level 1, you bring together ten of the sub
pieces. These ten of these pieces will be put together and once they are put together, they
become a bigger piece. Now you have this bigger piece in which you have ten of the
original pieces that are together. Eventually, this becomes a sub assembled part of the
whole of the watch.
Now, in the case of level 2, you have ten of these sub assembled pieces and they come
together and then they form another larger piece. And in the case of level 3, you had ten
of these pieces together and all of these ten come together and then they make the watch.
Now, in this case let us call these smaller pieces as, let us say that this is “a”, this is “b”,
this is “c” and then this is “d”. Now, in the watch d, “d” has ten elements of “c”. Now,
each element of c is ten elements of b and each element of b is ten elements of “a”. So,
altogether we have 1000 pieces of “a”, which is what we had in the case of Tempus as
well. So, this is “a” and this also is “a”
So, you have 1000 pieces together, but then because in the case of Hora, all of these pieces
were sub assembled and made into an organization.
(Refer Slide Time: 07:31)

This was an organization in which you had a hierarchy. So, here you have all the a’s, here
you have all the b’s, here you have all the c’s. So, all the a’s come together to form b’s, all
the b’s come together to form c’s and all the c’s come together to make the whole watch.

Now, if you have such an organization, what happens is that suppose Hora had come to
this stage. He had prepared or he was in the process of making a “c”, so he had say nine
elements of “b” that were together. Only one more element had to be put in and the phone
rang. So, what would happen is that these nine pieces of “b”, but again shattered down and
become nine individual pieces of “b”. But then, when Hora has attended the phone call
when he comes back, he will just have to put these nine elements together, put one more
and he has a “c”.
So, at every stage, here you can observe that the amount of work that is lost, if there is any
error, is very little as compared to the case of Tempus in which the amount of work that
would be lost because of any error would be tremendous.
(Refer Slide Time: 08:51)

So, if we had to put it graphically, in the case of Tempus, suppose, say this is the cut off.
So, this is 1000 a’s or the watch. Now, in this case, if you are able to reach this point, you
have made a watch. But, what happened in the case of Hora was that he had reached
somewhere like here and then the phone rang and then he had to start from 0, then again
he went till this point again, the phone rang, he had to start from 0. So, here you have the
pieces together versus the time.
Now, you would observe in this case that there could be situations in which the whole day
passes and Hora is not able to make even a single watch because every time the phone
rings, the watch goes down to all it is sub elements and becomes nothing.

(Refer Slide Time: 10:01)

Whereas, in the case of Tempus what happens is that, here also we have this 1000 piece
watch. Now, what happens is that even if he has reached till this stage and the phone rings,
there is only a small amount of work that each to be retreated because only that level of
organization will have to be remade and then he will progress forward, again when the
phone rings, he will progress to this point and then he has made a watch.
Then, he will start making another watch and probably in this case, the phone rang only
once and so, he was able to make two watches in a day. Here is why organization becomes
extremely important in the case of any system. From here, we come to Simon’s
hierarchical principle.

(Refer Slide Time: 10:53)

So, using this story, Simon came up with a principle that hierarchy emerges almost
inevitably through a wide variety of evolutionary processes for the simple reason that
hierarchical structures are stable. In the case of evolution, we have a series of changes that
go on to make an organism, a species or the whole system more and more fit for survival
and in that process, hierarchy would emerge almost inevitably. So, hierarchy becomes a
sanguine and it becomes a very important parameter if you want to have evolution that is
taking the system towards a bit of fitness and for the simple reason that hierarchical
structures are stable.
(Refer Slide Time: 11:47)

Now, where do we see hierarchy in nature? Well, you look at anything and you might find
some amount of hierarchy. Here we have a picture of a Roller that is eating a Centipede.
Now, in the case of a centipede, if you look here closely, you have a number of segments
and all of these segments have two legs.
(Refer Slide Time: 12:11)

So, if we draw a centipede, it would be something like this. So, you have different
segments, then you have the mouth parts and maybe you will have the n region. Now, all
of these segments have two legs. What nature has done in this case is that we have this
small structure that was made and a number of copies of this structure were made and then
they were put together. This is a very similar case as that of the watches of Hora. So, you
have this small piece that is constructed from its sub elements.
And then, a number of these pieces are then put together to create the next level of
organization. Similarly, if you look at your hands, all the fingers have these three
structures. So, why these three structures, here we also we are seeing the same thing.
We are observing segmentation as we had observed in the case and these segments are also
very similar to what we had observed in the case of this Centipede. And you will observe
the same thing everywhere when you look around. You will find it in centipede, you will
find this in Millipedes, you will find this in Caterpillars, you will find this in Earthworms,
you will find it even in our bodies.

So, for instance, if you have a look at your hands, so, the fingers are having these three
segments everywhere. You have a look at the vertebral column that holds our spinal cord
and there also we have a number of bones that are very similar in shapes and then once
these bones are constructed, they are put together.
So, essentially we are observing these levels of organization when we look around in
nature and in the case of this organization, what we observe is that we have one level of
structures that is call them “a”, that are combined together to make a structure called b,
that are combined together to make a structure called “c” and so on. And whenever we
have such an organization, we also observe the emergent principle.
(Refer Slide Time: 14:33)

Now, the emergent principle says that the whole is greater than the sum of the parts or the
whole has properties that its parts do not have.
Coming back to our example of the Centipede, we will observe that this portion, this is a
small segment of a Centipede. It has got some properties, it has a particular weight, it has
a particular size and shape, it has these two legs. But once you have put all these small
parts together to construct the Centipede, the Centipede has properties that are very
different from those of these smaller segments. So, it incorporates the properties of the
segments, but by coming together as a larger organization, it also gets some new properties.
So, the whole is greater than the sum of it is parts and the whole has properties that it is
parts do not have.

(Refer Slide Time: 15:35)

Now, we look at some more examples of the emergent principle. Here is an example of
fire ants. Now, fire ants are ants that are found in South America and these ants are called
fire ants because they are extremely prone to attacking other organisms and also because
if they bite you, it will feel as if your body parts are on fire. It has got a very pungent, a
very irritating bite. In the case of these ants, we observe that these are small insects, but
then when they come together, when they form an organization that will give out some
new properties. In this paper, we see fire ants self-assemble into waterproof rafts to survive
(Refer Slide Time: 16:25)

Now, what happens in this case is that if you have a low lying area and you have an ant
and in this area, suppose you have a lot of rain and there is some amount of inundation.
Now, if you had ants that were separate from each other; all of these ants would die off
because they are all submerged with water. They would not have access to air. To avoid
such a situation, to avoid death, what these ants do is that they come together.
All of these ants will come together, they will attach themselves to each other and they
will form a new structure. In this structure, you will even have air that is trapped inside
this structure to make the whole of this structure buoyant. So, as we can observe in this
image here, you have a group of these ants that are together and inside this structure, inside
this organization will be having a number of air pockets that will make this whole structure
buoyant and if you put this structure onto the surface of water, this structure will float.
Now, once you have a structure like this, what happens is that, all these ants that are on
the top are outside of water. So, they have an access; a free access to air; whereas, even
these ants that are touching the water, their body is not completely submerged. So, in this
case, they also get some access to air and the whole colony is able to survive and if you
look at the electron micrographs of these ants that are together, we will find that their
mandibles or their mouthparts are attached together in a manner that they are not biting
the other individual, but they are together in the form of this organization.
And what happens when you have this organization is that, this organization even if you
have lots of water, this organization will float and when it floats, it will move with the
water and once it finds a tree somewhere, then this organization will then slowly disperse
and then they will climb the trees. So, this is one emergent property an individual ant might
drown in water, but because of this property, because of this emergent property, they are
able to survive. So, again here the whole is greater than the sum of it is parts.

(Refer Slide Time: 19:07)

Here is another example when they are forming these rafts you can study their properties
and how the properties change?
So, if you look at this image, here we see an ant and on this ant, we have a drop of water
that is put on the top. And here we have a raft and here also we see a drop of water that is
put on top of the raft. Now, we can study the properties of the surfaces of the ant and that
of the raft using this drop of water and by having a look at the contact angles that are being
made here.
(Refer Slide Time: 19:49)

Now, for any surface, if you put a drop of water and if the surface wets because of the
water, so it is considered a surface such as paper. Now, if you put a drop of water on the
paper, this is a water drop. So, once you put a drop of water on the paper, it will subtend
an angle that is an acute angle which would show that the paper is hydrophilic. Now, if
you put a drop of water on another surface such as the surface of wax, here water will
subtend an angle that is an obtuse angle which would give us the information that wax is
Now, hydro is water, “philic” is loving and “phobic” is hating or someone who is afraid
of. In the case of paper, because paper is hydrophilic so, it is in love with water, it wants
to have as much water as is possible. So, it attracts water to its surface because of which
we get an acute angle, @whereas, in the case of wax, because it is hydrophobic it is afraid
of water, it wants to repel water as much as possible. So, it tries to clear of these surfaces.
So, this surface is now cleared off and it wants to have as little contact with water as
possible because of which it forms an obtuse angle. Now, by looking at these angles, we
can understand the level of hydrophobicity of surfaces.
Now, if we come back to the images, here we are observing that there is a drop of water
on top of the ant and this outer surface is called the cuticle. Now, this cuticle is mildly
hydrophobic because it is subtending an obtuse angle, but if you put this drop of water on
a raft of ants, the angle that is subtended, it becomes even more obtuse.
So, the level of hydrophobicity increases, so that the amount of water repelling nature of
the ants also increases. And at the same time, we can also observe that if you put a single
ant inside water it will try to grab a small pocket of air, but if you have this whole raft that
is that is drowned using a stick, it will have so much amount of air that it will be much
more buoyant as compared to a single ant.
So, the whole will have properties that are derived from the components, but are also there
will be some emergent properties that are different from all the components that are
combined together.

(Refer Slide Time: 23:13)

Now, with this, we can also observe number of liquid like properties of these ant rafts. So,
for instance, here we have one such raft that is put on top of a Petridish, now if you put
another petridish on top and if you press this and then if you release it, it will come back
to the original shape.
So, essentially this group is now getting some properties of elasticity. Then, if you put one
such group into say a pipette and then you put a ball of lead inside this pipette, you will
observe that this ball of lead slowly moves down. It will behave very much like a very
viscous liquid, something like honey.

(Refer Slide Time: 24:01)

Suppose you have two containers and one container has water and the second container
has honey, now you are taking a ball of lead and you are dropping it in both of these
containers. In the case of water, because the level of viscosity is this, the lead will fall
down very fast whereas, in the case of honey, it will have a slower speed. Now, in the case
of ants, when you are putting them together because they are combining themselves with
each other, they are also getting the properties of viscosity which is an emergent property.
So, if you talk about a single ant, you would not have a property of viscosity because it is
a single element, but you put all of these together and they get an emergent property which
is viscosity and also emergent properties such as elasticity.
So, elasticity and viscosity are things that we are getting as emergent properties.

(Refer Slide Time: 25:07)

Now, emergent properties are found nearly everywhere in nature. For instance, if you look
at a termite mound; so, a termite again is a small insect and such a small insect and only
do “n” number of items in its life. But you put a whole colony of termites together and
they will form of these structures, these mounds like structures which again have their own
properties. Now, these structures are made in a manner that you have ample amount of air
circulation, you have thermal regulation and so on.
If we talk about the construction of any building, there would be a supervisor that would
be coordinating the actions of all of these; all the people who are making the building
whereas, in this case there is no such supervisor. All these termites are just doing their own
jobs and by doing their own jobs they construct this structure. So, this again is an emergent
property, you just use a single termite and it will not be able to make a mount. But because
of the collective actions, they get this property that they are able to construct this particular

(Refer Slide Time: 26:21)

Now, if you look at the level of organization in the biological world. Whenever we are
talking about organization, we say that we have a sub cellular organelles, cells, tissues,
organs and so on. So, if you look at any particular linkage say cell to tissue. So, tissue will
be comprised of a number of cells. Here we will observe a hierarchical principle or
Simon’s principle that will operate. You will have cells as independent units, you put these
cells together and they form the next level of structure which is a tissue. We will observe
hierarchical structures everywhere. And second, we will observe emergent properties
everywhere. So, a cell has certain properties. But when you put all these cells together they
form the tissue. So, tissue will be comprised of cells, but we will also have a number of
properties that are not found in cells. It will also have a number of emergent properties.
When we look at organization, these are two things to keep in mind. Now, what are the
levels of organization in the biological world? So, we begin with the sub cellular
organelles. A number of these sub cellular organelles will come together and form the cell.
Now, a sub cellular organelle does not have any characteristics of life, but a cell is a living
entity. So, just by putting these organelles together, you get a new emergent property which
is life in the form of a cell.
Then, you put cells together and they form a tissue. Tissues come together to form organs.
Organs come together to form an organ system followed by an organism. Now, an
organism is the basic entity from which we can start our analysis, especially in the case of
ecology. So, you put organisms together and these organisms are of the same type. So,

they form a population. You put a number of populations together, they form a community.
Now, till community we have all the biological elements. Now, you put community which
is a biological element together with the abiotic elements and you get the ecosystem; a
number of ecosystems together will form a biome and a number of biomes together will
form the biosphere or the life sphere that is formed on our planet.
Now, we will have a look at all of these levels of organization in more detail.
A sub cellular organelle is a specialized subunit within a cell that has a specific function.
So, you might remember these from your school days, we have mitochondria which are
organelles that are responsible for the generation of energy inside cells. We have
chloroplasts that are found in the plant cells and are responsible for photosynthesis. We
have nucleus which is an organelle that stores DNA and all the hereditary information
together inside. We have vacuoles which are like waste bags or specialized containers
inside the cells to store something.
All of these are specialized subunits within the cell and all of them have a specific

(Refer Slide Time: 29:55)

Now, if we have a look at the epidermis of an onion. You take an onion, you separate out
it is outer layer, then you stain it with stains and then you have a look. Here we will observe
that there are cells. This is a plant cell and here we observe a nucleus. Nucleus is a sub
cellular organelle; sub cellular because this is at a level that is below that of the cell. So,
this is a sub cell organelle; but an organ is an organization that is performing the specific
function. Here also these organelles are performing some specific functions but because
they are very small in size we do not call them organs, we call them organelles when they
are sub cellular in size. Here we observe sub cellular organelles within a cell.
(Refer Slide Time: 30:55)

Now, a number of these sub cellular organelles will come together to form the cell and the
cell is the basic structural, functional and biological unit of all known living organisms or
the smallest unit of life. It is the basic structural, functional and biological unit. So, all the
organisms have are made up of a single cell or a number of cells.
One cell in the case of a unicellular organisms such as bacteria and multiple cells in the
case of multi cellular organisms such as human beings. This is the basic structural unit.
The structure of the body will be made by cells. These are the basic functional units
because they will be performing all the functions and they are responsible for all the
emergent functions that are there in the body and they are the basic biological units.
Because all the processes like respiration or say, cell division; they all happen at the level
of the cells. They are the basic structural, function and biological units of all known living
organisms or the smallest unit of life and we can observe cells very easily in the case of
onion, or in the case of animals if you make a smear of blood, you will be able to see the
red blood cells. If you make a smear of your cheek cells, you will be able to see a number
of epithelial cells and so on.
(Refer Slide Time: 32:23)

Now, from cells we move on to tissues. An ensemble of similar cells and their extracellular
matrix from the same origin that together carry out a specific function.

(Refer Slide Time: 32:49)

In the case of a tissue, you will have a number of cells together. You have cells and these
cells are embedded in an extracellular matrix. These cells together with the extracellular
matrix will form a tissue. It is an ensemble of similar cells. These cells have to be similar,
if they are coming from different origins, if they are different cells, then probably we are
looking at multiple tissues together. But, an ensemble of similar cells and their
extracellular matrix from the same origin that together carry out a specific function.
(Refer Slide Time: 33:55)

Now, what could this function be? When we look at the onion cells, when we are looking
at the epidermis tissue of the onion cells, they are performing a very specific function and
that function is to keep water inside; that function is to protect the onion bulk from outside
environment. So, this is specific function that is being done by this tissue which is the
epidermis tissue and this tissue will comprise of a number of epidermal cells together with
the extracellular matrix that is binding these cells together and this is the matrix in which
these cells are embedded inside.
(Refer Slide Time: 34:15)

Now you put a number of tissues together, so, tissues from different origins together and
you get an organ. Now, organs are collections of tissues with similar functions. So, for
instance, intestines are organs.

(Refer Slide Time: 34:25)

In an intestine, you will have a number of different tissues.
(Refer Slide Time: 34:33)

If we look at a cross section of intestine, we will be having these tissues which are the
endothelial tissues. We will also be having some blood vessels which are vascular tissues;
we will also be having some muscular tissues. We have blood vessels, we have the
muscular tissues, we have the endothelial tissues and so on.

All of these different tissues from different origins, they are coming together to perform a
specific function. In this case, the function is to absorb nutrients that we are getting from
In this case, we are looking at the larvae of a drosophila and we have stained the intestines
using a blue coloured stain and here you can observe one organ. Another organ, say, the
mouth of the organism. So, mouth is also comprised of a number of tissues from different
sources. Even in the case of our mouth, we will be having epithelial cells on the inside, we
will also be having blood vessels, we have muscular tissues, we also have the skeletal
tissues inside and so on.
(Refer Slide Time: 36:03)

The next level of organization is an organ system; a group of organs that work together to
perform one or more functions. It is a group of organs that are working together to perform
some function. For instance, an organ system is the digestive system. Digestive system
comprises of a number of organs. It will comprise of the mouth parts, it will comprise of
the intestines, it will comprise of the stomach, in our case it also comprised of the liver, it
will comprise of pancreas, small intestines, large intestines, rectum and all these different
organs together will form an organ system which is the digestive system. Now, all these
organs are performing some specialized functions and they are put together to perform a
next higher level of function.

So, for instance, in the case of our mouth, the mouth is only chewing the food, but then
after chewing it goes through the oesophagus which is a conduit medium then it goes into
the stomach which performs the function of a reservoir in which the food items are put
into an acidic medium and then a number of enzymes are added there.
Then it moves into the small intestines which provides a basic medium and then it moves
to the large intestine which will absorb quite a lot of water from the food materials that we
have ingested. Then, it will move to rectum and anus through which those portions of the
food that are not absorbed by the body are then gotten rid off. Now, all of these different
organs are performing just one function together which is the consumption, digestion and
ejection of the food. So, all of these will together form the digestive system.
(Refer Slide Time: 37:47)

The next level of organization is an organism. An organism is an individual entity that
exhibits the properties of life. Now, when we see properties of life, what are those? This
organism should be able to get it is own food. It should be able to digest the food; it should
be able to assimilate the nutrients inside. Then, probably another function of life would be
movement. There are a number of organisms that do not move like plants, but movement
is also another function of life. So, like all the animals move. Then, another basic function
of life is procreation. So, they give rise to their offsprings. All these functions of life that
are together performed; are performed in an entity that is called the organism.