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Module 1: Human Ecology and Ecology of Change

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Introduction and Impacts

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Today, we begin a new module which is topics in Human Ecology. Throughout this course,
we have seen what are the different biotic and abiotic factors that play a big role in
deciding, where an organism will be found; how would that organism will be distributed,
how any organism gets energy or nutrients from its surroundings and so on. These days,
the human beings are able to exert a very large amount of influence on all of these
ecosystems because of our huge populations, because of our technological advances,
because of our affluence and so on.
So the impact of human beings on ecology becomes very important. And also we can make
use of the principles of ecology to understand how the human population is growing. So,
these are the things that we understand in human ecology.
(Refer Slide Time: 01:14)

This module is going to have three lectures. The first one is Introduction and impacts. Why
this field is important? What kind of things do we learn in this particular field? and so on.

The second lecture will be human population growth in food requirements. In this case,
we will make use of the learnings from ecology, especially the growth of populations to
understand the growth rate of the human population. What is the rate at which we are
growing? Is there a cap to this particular growth rate? or Are we going to have an ever
increasing population? or Is this population going to reduce after a time or maybe becomes
stabilized after a time? What are the factors that are responsible for that? And we will also
look at our food requirements.
There is this particular Malthusian theory that we had referred to even in our introductory
lectures; now we will look at that theory in more detail. According to Thomas Malthus,
this theory tells us that the human population increases in a geometric progression. So,
essentially from 1 to 2 from 2 to 4, then 4 to 8 and 8 to 16 and so on. So, it becomes a
geometric progression increase. Whereas the food requirements only increase in arithmetic
progression; so, from 1 to 2 then 2 to 3, then 3 to 4 and so on. Malthus had predicted that
the food requirements will ultimately act as a cap on the growth rate of human populations,
because if you do not have food; so people will get into misery and they will start dying.
But then this theory had predicted that will have a severe food shortage say in the early
19th century, but even today we do not have a food shortage. We will have a look at what
are the factors that have enabled us to move out of the Malthusian trap. We will look at
those topics in more detail when we are talking about sustainable development. Because
sustainable development is one mode of development in which we use our technologies in
such a way, that we are able to use the resources but at the same time, we are also able to
save the resources for the future generations.

(Refer Slide Time: 03:38)

Let us begin with the first lecture. Here, the question is, Are there any limits to growth? Is
there a limit to the growth rate of population? Is there a limit to the growth rate of
technology? Is there a limit to the impacts that we are going to have on the biosphere? and
so on.
(Refer Slide Time: 03:59)

In this context, Paul Ehrlich had written this book The Population Bomb. This book, it is
a bit Malthusian in its outlook, but then this book also states that the human population
growth is moving at such a rapid stance that it is a severe problem these days. And then

this is a ticking time bomb that needs to be stopped. Why do we say that human beings or
the size of our population has now becoming an issue for the biosphere?
(Refer Slide Time: 04:42)

There are a number of reasons and the most important is that these days, we are living in
the Anthropocene era. Anthropocene is a geological time scale which some scholars
believe that it started with the atom bomb testing or the trinity testing in 1945. And we
take this particular time point as that the point from where the human beings started to
have an impact on the ecosystem that was much greater than any other impact.
If we consider the impacts of say carnivores on an ecosystem and let us consider the impact
of human beings on an ecosystem; so the impact of human beings is much greater than
even those of the keystones species or those of the top carnivores or the apex predators
and so on.
When we say that our impact has become so large that we have demarcated this geological
time scale as Anthropocene. Now, anthropoce as we know is the human beings. So,
anthropocene is the time period of the human beings or the latest time period where the
human beings are having a great amount of influence.

(Refer Slide Time: 05:55)

It is a proposed epoch. Epoch is a time duration dating from the commencement of
significant human impact on human on earth’s geology and ecosystems including, but not
limited to anthropogenic climate change.
It is a proposed epoch, there are some scholars that have already started using this term.
But then there are some others who still call it a proposed epoch because it has not yet
been finalized. Whether we take this 1945 as a date from which we started to have a very
substantial impact or maybe the industrial revolution or maybe somewhere in between and
so on.
But then we define it as a proposed epoch dating from the commencement of significant
human impact on earth’s geology and ecosystems. Now, not only are we impacting the
ecosystems, the biotic organisms that are living on earth, but also the geology of the earth
and this is including but not limited to anthropogenic climate change.

(Refer Slide Time: 07:01)

What are the kinds of impacts that we are talking about? The first impact is that of
overconsumption; more number of people, so more amount of resources that are required,
plus for every particular individual human being, the amount of consumption has increased
through the ages.
For instance, if you talk about your grandparents. Your grandparents might not be having
televisions in their homes, they probably did not have a computer in their homes, they did
not require Wi-Fi, there were very less number of air conditioners that we had in this
country.
The amount of resources that were consumed by them was much limited. They probably
either never flew in their youth or probably the only flew for a few times. But then, these
days we are using aeroplanes as a very common medium of transportation. The amount of
resources that we are consuming, so if you talk about moment on land versus moment on
an aeroplane; an aeroplane consumes much more amount of fossil fuels.
If you talk about say the consumption of cotton. The earlier generations used to have a
fewer number of clothes as compared to what we are having today. If we talk about the
amount of electrical energy that is being used. These days, our amount of electrical
consumption is much greater than those of our ancestors; or if we talk about the amount
of fossil fuel that we have been using.

These days, most of us are moving in cars and those cars are probably air-conditioned
whereas, if you talk about the earlier generations they probably were using bicycles or
maybe scooters. So, the amount of fossil fuel that has been consumed anywhere and
everywhere, it has increased drastically. When you talk about overconsumption, there are
two reasons; one is that the population has increased. So, more number of people so more
amount of resources are needed and second the per capita requirement or the per capita
usage of different resources has increased a lot; so that is overconsumption.
If we even talk about the amount of agricultural resources that we have been using, so if
we talk about say, the population of the earth say, 100 years back. So, they required less
number of food grains.
So, they required less number or less amount of water to irrigate their fields, but then these
days the amount of land is more, the amount of water requirement is more. So, there is an
overconsumption in a number of sectors. The second impact is that of habitat destruction.
Now, this is very closely related to overconsumption. If you have a requirement for more
amount of iron and steel. So, you require more amount of iron ore, you require more
amount of coal, more amount of limestone. In that case, where are you going to get all
these resources from, because you require all of these resources to satisfy the needs and
the wants of the existing population.
So, you are going to get these resources by mining in different areas. Now mining leads to
a heavy amount of habitat destruction in a number of areas. Or let us say, talk about in the
agriculture sector. In the case of agriculture, earlier we were using less amount of
fertilizers, maybe more amount of manures, less of fertilizers, then there were not many
pesticides that were available in those days and so on.
These days, because we have a huge population to feed, so it is essential that you have
more amount of food grains that are being produced. Now to produce more amount of food
grains we are using more and more amounts of fertilizers, we are using more and more
amount of pesticides. Throughout this course, we had this theme running that if you are
using pesticides and suppose the food grains now have pesticides on them and even in
those areas where the concentration of pesticide is very less, even in those areas as you
move up with the food chain. So, if there is say, a grasshopper which is there on your fields
and when you sprayed your fields with pesticides. So, a number of grasshoppers died off,

but then their carcasses still remain there. Now there could be some birds that come and
feed on these grasshoppers.
In that case, they are getting exposed to the pesticides or maybe the concentration of
pesticide that was sprayed was not large enough to kill all the grasshoppers. So, there are
a few that are still living in that area or probably there are a few grasshoppers that now
have become resistant to the impact of pesticides, because we have seen that there is this
natural selection that is acting at all times.
Even in the case of a grasshopper population, you will be having some individuals that are
more susceptible to the impact of pesticides.
(Refer Slide Time: 12:30)

Let us consider a big population of grasshoppers and suppose grasshoppers are one pest
that we are trying to counteract using the pesticides. Now, even in this population there
will be some individuals that are more resistant to the impact of pesticides and then there
are some individuals that are less resistant to the impact of pesticides. Now when you spray
pesticide on this population, there will be a large amount of mortality in this particular
population.
Suppose all of these die out, but then still there will be a few that will remain. So, these
three individuals have now remained probably because their bodies were much better at
pushing these pesticides out of their system or probably because they had a behavioral

response, so, they were sneaking into the crevices that were available in the soil so that
they were not exposed to the pesticides. So, there could be n number of reasons or maybe
the amount of metabolism in their bodies is such that they are able to counteract the
pesticides. Now in this particular situation when you have a huge amount of mortality; let
us say all of these individuals have died out.
So, all of these individuals are now dead and you are only left with three individuals and
all these three individuals are those individuals that are resistant or slightly resistant to the
impact of the pesticides. Now what would happen in the next generation?
(Refer Slide Time: 14:18)

So, there are these three individuals that are surviving. They will mate they will give rise
to eggs and then in the next generation, when we again have a large population of these
grasshoppers, now in that case, either all or probably most of these individuals will now
be more resistant to the impact of these pesticides.
Now, what happens? You spray the population with pesticides again and again those
individuals that are not resistant they die off, but here we can observe that there are lesser
number of mortalities or lesser percentage of mortality as compared to what we had seen
in the previous instance. In the previous instance, everybody except these three
grasshoppers were dead because of the impact of pesticides.

In this case, there are only these five individuals that die off and then, you have all these
individuals that are surviving.
(Refer Slide Time: 15:19)

What will happen in a few generations from now is that everybody that is there in this
population will have these resistance genes; because these resistance genes are what are
making these individuals more fit for survival.
When we are talking about the term fitness, here we have this particular gene or this
particular trait that is providing these grasshoppers fitness, either because of the chemical
metabolism that they have or probably because they are better at taking these pesticides
out of their system or some behavioral adaptations. If there are some grasshoppers that
they prefer living in the crevices. So, they come out, feed and then move into the crevices.
In this case, most of these grasshoppers will now have these kinds of behavioral selections.
So, they will always prefer living in the crevices and once that happens, what will happen
is that you will have to spray more and more amount of pesticides to have the desired
impact; because the farmer wants to have this field that is free of pests.
So, the farmer would have to spray pesticides, but then the amount of pesticides that will
have to be sprayed will go on increasing with every generation because with every passing
generation, the insects or the pests that are there in the system are becoming more and
more resistant. So, the amount of pesticide that needs to be incorporated will also increase.

What will happen to all these pesticides? These pesticides after a while, they will leach out
into the groundwater because you have ample amount of pesticides everywhere; so if there
is rain, so along with the rainwater that seeps and becomes a part of the groundwater table,
these pesticides will also become a part of the ground water table or probably these
pesticides will move along with the different streams.
(Refer Slide Time: 17:22)

If you have this particular area which is a farm land and when you have rainfall in this
area. So, you can always observe that there are some small streams that are moving away
from these agricultural forms. And then these streams then join together and then they
become a part of the river and from there it can move into the seas or probably this will go
and drain a small pond somewhere.
Now what will happen to all these pesticides is that they will either go into the ground or
they will start accumulating in the water bodies. Of course, there will be a large amount
that will degrade with time, because there are also a number of influences or the impact of
a number of elements such as there would be oxygenation of the pesticide which would
probably render it harmless or probably these pesticides when they are exposed to the sun’s
rays; so that will also lead to some amount of scission reactions as we had seen in the case
of plastics.
But then, whatever happens there would be some amount of pesticides that would start
leaching into the groundwater table. Here we have the groundwater, so some amount of

pesticides will start getting into the groundwater or they will start reaching into the lakes
or they will start reaching into the rivers.
Once that happens, we will see the impacts of these pesticides not only in these particular
fields, but also in the wider ecosystem as well. Let us say that even if they are not able to
reach into these water bodies, what will happen is that they will start accumulating in the
soil. Now these pesticides were meant to, say, kill off the grasshoppers which are feeding
on the crops, but then when your soil starts becoming saturated with these pesticides, they
will start impacting a number of other organisms. Probably they will start killing off the
earthworms. Now we have seen earlier that earthworms are decomposers, so they are
detritus feeders. So, if there is any amount of organic matter that is there in this soil, they
will feed on it, they will break it up into smaller portions, and then those smaller portions
will be preferentially acted upon by different microorganisms. Now what happens if you
have an ecosystem? Here we are talking about the farmland ecosystem and this farmland
ecosystem is devoid of all the detritivores or divide of all the decomposers. Now if you
have such a system, this system will start to collapse in a short while.
So, if there is any leaf that has fallen onto the soil. So, this leaf will not be eaten up; it will
start accumulating then and there. Now, there are also a number of other impacts that we
will see, so, like we talked about the fertilizers and if you have fertilizers that reached into
a lake, you will start observing algal bloom here. If they start reaching into the rivers, so
here now we are talking about the fertilizers, fertilizers will also start moving into the
rivers; once that happens again you will see a larger amount of primary productivity.
Every act of the human beings is now putting a lot of influence on the different ecosystems.
What happens to these fertilizers? So, let us talk about say ammonium sulfate. Now, if we
have ammonium sulfate and in this particular system the nitrogen is taken up by the plant,
what happens to the sulfate? This sulfate starts accumulating in the soil. Once that happens,
the soil starts to have more and more amount of these salts. It leads to salinity in the system.

(Refer Slide Time: 21:39)

We had seen in the case of the Chilika lagoon; so when we talked about Chilika lagoon,
we said that we have this big sized lagoon and then, it is separated from the seeds with this
sand bars and here we have the Bay of Bengal and you have a number of streams that are
coming to the Chilika Lake.
In this case, the amount of salinity that we have will be very high here, which is close to
the seas and it will be very less here. And in this case, we say that we have different
organisms that occupy this sector, different organisms that occupy this sector and different
organisms that occupy this sector. Now in your farmlands, if you start having more and
more amount of salts, you are again changing the ecosystem in a way that it becomes
difficult for a number of organisms to live there. Now with all of these, we are talking
about the destruction of a number of habitats.
Another influence of human beings on the ecosystem is that of habitat destruction. This
habitat destruction may at times lead to desertification as well; now we have seen the
causes and impacts of desertification in earlier lectures. So, if there is a heavy amount of
over grazing in an area, or the plants are eaten up by say, goats or sheep, in that case the
soil becomes exposed; because there is no longer the root system to hold the soil. And the
soil starts moving, it starts drying and in a short time you have converted this very fertile
area into a desert; that is also another impact of human beings on the environment.

Let us talk about ocean acidification. What is happening is that we are using a huge amount
of fossil fuels in our vehicles, for power generation, in a number of industries and so on.
Now when we talk about the use of fossil fuels what we are doing is, we are taking out
these fossil fuels which are accumulated carbon which is say millions of years old. They
were forests a few million years back that because of some reason, they got submerged
into the earth. Probably, there was some amount of earthquake and because of that
earthquake, all these forests they moved inside the earth. Now with the high amount of
temperature and the high amount of pressure and over long periods of time, the other
chemical constituents started moving out and what remained was the coals.
If you take these coals out and you start to burn these coal; so in that case, you are taking
out all these carbon that was stored inside the earth for a very long period of time and by
burning this coal, you are releasing carbon dioxide into the atmosphere.
(Refer Slide Time: 24:49)

If you have carbon dioxide, so if you have CO2 and when it reacts with H2O you get
H2CO3, which is the carbonic acid. Now where do you get so much amount of water? You
have a huge amount of water that is stored in the oceans. So, by releasing a huge amount
of carbon dioxide into the atmosphere, we are increasing the concentration of carbonic
acid that is there in the oceans.
So, that is again changing the pH of the oceans and as we know for every organism there
is a very definite level of environmental conditions that it can tolerate. We talked about

the Shelford’s law of tolerance. So, probably there will be a number of organisms that will
not be able to tolerate a low pH, an acidic environment.
(Refer Slide Time: 25:43)

For instance, if you take a beaker and in this beaker, say you put a few shells of the
mollusks. Here you have a few shells of the mollusk or probably you are keeping a few
corals inside. You just keep a few corals inside and then, you fill this beaker with an acid.
Let us say you fill this beaker up with carbonic acid, what will happen is that all the calcium
carbonate that was stored in all of these animal bodies that will start releasing off the
carbon dioxide.
You will see all these carbon dioxide bubbles that will start coming out and in a short
period of time all of these organisms, their bodies will be completely dissolved in the acid.
Now when we are talking about ocean acidification, this is something that has continuously
happening in the oceans. If you want to have a shell and that shell has to be made out of
carbon of calcium carbonate. So, you need to have a basic environment or probably a
neutral environment, you cannot have an acidic environment. So, with more in more
amount of ocean acidification we are seeing the deaths of a number of organisms such as
corals.
So, we see that the coral start bleaching off and in a short period they start dying off. And
corals being keystone species they will also impact a number of other organisms. So, that

is also a big human impact on the environment or let us talk about ozone depletion. Now
if we release chlorofluorocarbons they eat up the ozone that is there in the stratosphere.
The layer of ozone is what protects the life on earth from the UV radiations of the sun.
Because that is able to use up the UV radiation and so the amount of UV radiation that
reaches to the ground is less. Now if you take off the ozone layer, more and more amount
of UV radiation will start coming to the earth, what will that lead to? That will lead to
things like cataracts or maybe burning of the skin of different animals or probably more
amount of mutations that we will start seeing in a number of organisms and so on.
So, that is another impact of human beings on the environment. Or changes in the
biogeochemical cycles such as the nitrogen cycle; naturally there is a fixed amount of
nitrogen that can be taken up by the soil because of the natural processes, such as lightning
or say biological nitrogen fixation. But then using our industrial processes such as the
Haber process that we have seen earlier, we are putting in much more amount of nitrogen
into the soils.
So, we are playing with different biogeochemical cycles such as the nitrogen cycle causing
other impacts on the environment; or loss of biodiversity and extinctions that we had
discussed before. Or changes in the distribution of organisms or changes in biodiversity,
especially because of climate change.
(Refer Slide Time: 29:04)

In this case we have seen that if you have certain organisms which have say, this particular
range and this is south, this is north and then if you have more amount of global warming
or more amount of climate and then probably the range will shift more northward so that
there is a lower temperature that is available for these organisms.
So, changes in distribution of organisms, changes in biodiversity, also things like soil
erosion and changes in geo morphology or deposits that are derived from concrete, lime,
mortar and other calcareous materials outside the cave environment. Here what we are
seeing is that if you have more amount of tillage on the ground, if you are ploughing your
fields often so there will be more amount of soil erosion; because now the soil is more or
less unbound.
If there is any wind or if there is water flow, this soil will get eroded away and then it will
move to other areas. It will lead to changes in the geomorphology. For instance, if we talk
about the Sundarbans area.
(Refer Slide Time: 30:15)

In the case of any delta so let us say that here we are representing the Sundarbans delta.
You have a number of distributaries that are coming out of the rivers and then, because
these rivers have been bringing huge amount of sediments; in these deltas because you are
now exposed to a saline environment because it is close to the seas.

These sediments start coming out of the water and they start getting deposited here which
is how we form a delta. So, in the case of a delta the sediments that were brought by the
rivers from the upper areas such as the mountains or the plains, they come to these delta
areas and they get deposited here. Now if we play with the amount of sediment load, say
if you have more amount of ploughing in the upslope area. There are a number of
agricultural fields and they are not being managed properly. So, there is a heavy amount
of sediment that is coming into the rivers, what happens in that case? The size of the delta
increases, because you have more amount of sediments that are now available in this area
or suppose you reduce the amount of sediments. Let us say, we constructed a dam here
and because of this dam all the sediments that this river was bringing it gets accumulated
here only.
So, it does not reach the deltas; in that case, the size of the deltas will start reducing. These
impacts of human beings are leading to soil erosion, they are leading to changes in the
geomorphology; also because we have created a number of artificial materials such as
concrete, lime and mortar, we are seeing some amount of stalactite like substances that are
coming, not in the cave environment, but outside.
(Refer Slide Time: 32:32)

What are stalactites? If you have say a cave and in this cave this area is a full of calcium
carbonate and you have water that is dripping from the top to this bottom. In this case,
some amount of calcium carbonate will start accumulating here because it is getting

deposited along with the water and if it is getting crystallized there. And then, we will also
see some amount of calcium carbonate deposit that starts building up at the bottom. So,
the upper portions are known as stalactites and the bottom portion is known as stalagmite
and if both of these continue for a very long period of time. So, they go on increasing in
their sizes and then after a while, they will meet each other and once that happens; the
whole thing will be called a column.
Now, these formations such as stalactites,stalagmites and columns which were earlier seen
only in the cave environments produce some very specific ecosystems and very specific
habitats for a number of organisms. But now, what is happening is that, you go to a parking
lot and in this parking lot, you see some amount of water that is dribbling out and then you
will start seeing these formations that are there in the parking lots as well. So, we are
changing the habitats in a number of areas which is also a big impact of human beings on
the environment.
(Refer Slide Time: 34:22)

Let us talk about the changes in stratigraphy due to increased sediment load and deposition
as in the case of deltas or talking about the changes in the elements in the atmosphere, such
as Carbon-12 that is released from the fossil fuels and radionuclides that are released from
nuclear fallout and atomic reactors. What we are talking about here is that, if we consider
the element carbon and carbon is there present in the case of carbon dioxide.

(Refer Slide Time: 34:44)

So, carbon is present in two isotopes: so carbon can be either carbon-14 or it can be carbon-
12. Now carbon-14 is continuously being produced and this element which is radioactive

element, it starts degrading with its own half life. And so the amount of carbon-14 to
carbon-12 that is there in the atmosphere, it remains constant because you have a constant
amount of carbon-12 and there is carbon-14 that has been produced at a continuous
constant rate. Now what happens when we burn up the fossil fuels is that the carbon that
was stored for a very long period of time so that has a very low amount of carbon-14.
Practically, you can say that it is more or less pure carbon-12, when you are burning it off,
so, you are changing the elementary or the isotope composition that is there in the
atmosphere, because you are increasing the amount of carbon-12 that is there in the
atmosphere.
When we talk about other radioactive nuclides or elements that have being released
because of the nuclear fallout in atomic reactors. Let us say you talk about strontium.
Strontium is not something that you normally find in the atmosphere or in the soil, but then
if there is a nuclear fallout say because of fukushima. So, you will see that there is a huge
amount of strontium that has been released into the atmosphere and has come into the soil.
What is very specific about strontium is that it is able to replace calcium that is there in
our bodies.