hello everybody my name is Zohir Chowdhury, and today we'll talk about I equal to PAT
model as it applies to population and health so there are always limits to population growth in
nature populations cannot grow exponentially indefinitely exploding population always reach
a size limit imposed by the shortage of one or more factors such as water space and nutrients
or by adverse conditions such as disease drought and temperature extremes the factors which
act jointly to limit our populations growth are termed the environmental resistance the
interplay of biotic potential and density dependent environmental resistant keeps a
population imbalance for a given region carrying capacity is the maximum number of individuals of
a given species that an area's resources can sustain indefinitely without significantly
depleting or degrading those resources determine the carrying capacity for most organisms is fairly
straightforward for humans carrying capacity it's much more complicated and we'll have
some examples later on for population which grow exponentially growth starts out slowly
then enters the rapid growth phase and then levels off when the carrying capacity for the
species has been reached the size of the population then fluctuates slightly above
or below the carrying the carrying capacity reproductive lap time may cause a population
to overshoot the carrying capacity temporarily reproductive lag time is the time required for
the birthrate to decline and the death rate to increase in response to resource limits
in this scenario the population will suffer a crash or die back as shown in here ANILCA and
areas carrying capacity is not static the carrying capacity may be lowered by resource destruction
and degradation during an overshoot period or extended to technological and social changes
an example of dieback occurred in Ireland after fungus infection destroyed the potato crop in 1845
during this potato famine approximately 1 million people died and three million people emigrated to
other countries increase food production due to improved agricultural practices control of many
diseases by modern medicine and the use of energy to make historically uninhabitable areas of earth
inhabitable are examples of things which can extend carrying capacity the question is how
long we will be able to keep increasing our population on a planet with finite size and
resources as we move to the next slide in here we'll learn about I equal to PA T model which
is the main highlight of this presentation this equation in this equation we can see I
which stands for human impact on the environment this I is equal to P population a affluence which
also expresses consumption per capita and tea technology which is the environmental impact per
unit of consumption in the IP glue tree in the IP equal to PA T equation the variables P represents
a population of an area such as for example the world or in the city of San Diego or in the state
of California or in the entire country United States since the rise of industrial societies
human population has been increasingly increasing exponentially and as a result total environmental
impact has also been increasing the variable a in the I equal to PT equation stands for affluence
it represents that average consumption of each person in the population as the consumption of
each person increases the total environmental impact increases as well the variable T in the
I equal to PT equation represents how resource intensive the production of affluence is how
much environmental impact is involved in creating transporting and disposing of the goods services
and amenities used dynode of tea is often tailored for the situation I equal to PT has
been applied to for example for a situation where the human impact and climate change is
being measured and appropriate image for team at big greenhouse gas emissions per unit of GDP
so let's start could you do some quick concept check the maximum number of individuals that a
particular habitat can support is called carrying capacity true or false true very
good so let's look at some examples of carrying capacity so by looking in this graph can you
tell me what is the population of the deer at the carrying capacity of the environment
yes it's d because you can look in here it's overshooting and it's going up high and is
slowly balancing at the carrying capacity and that is around 70 another concept
check which graph represents the maximum carrying capacity of a bacterial colony
that's correct it's the one in here this is not showing a carrying capacity this is
growing linearly this is decreasing linearly this is growing exponentially so we don't
know whether carrying capacity is whereas in here we can see that it is overshoot then it's
there's a die back and here is the carrying capacity somewhere around here now how have
humans been able to raise the environments carrying capacity for our species yes it's
a through technology through technological innovation so a related question do you think
humans are subject to limiting factors and ultimately a fixed carrying capacity if you
believe so yes although we have raised the carrying capacity there are limits to the
number of humans the earth can support so in this is saying that there may be limits be yes
but technology will keep raising the carrying capacity so it's not much of a problem C is
no humans are no longer constrained by the environmental limits due to our technology
and ability to manipulate the environment and D I don't care it really does not affect me so
definitely C is not the answer humans we are seeing a lot of issues out there
and we definitely do not have an unlimited carrying capacity the resources are limited
in the world so between a and B we are seeing the technology definitely has been
able to increase our carrying capacity by buf by far we are seeing that the carrying
capacity even though we can increase it there is a certain limit of humans
that the earth can support the resources are limited so the answer is probably a alright