help with birth rate and mortality rate

Question

if a country lowers it mortality rate w hile its birth rate remains the same I think the size of the population of the country will inccrease.  am I correct?

 

 

 

Answer 1

I disagree with the answer Ajay Z gave, because we don't know whether the population is increasing or decreasing initially. If the population was initially decreasing (I'll use the same assumption he presented that other population factors are constant) then that means the mortality rate was initially greater than the birth rate (note that the birth rate does not have to be zero for this to be true).  Therefore, we can't answer this question with the information provided, because we must know whether the population was initially increasing or decreasing, and we must also know how much the initial difference in the rates was and by how much the mortality rate decreases. Your answer that the population will increase assumes several things:

 

It assumes other factors are constant as Ajay Z stated.

It also assumes that the birth rate was positive as Ajay Z stated.

It makes the additional assumption that the mortality rate decreases to below the birth rate. (Note that this can be the case regardless of whether the mortality rate initially was greater than, less than, or equal to the birth rate.)

 

Basically, we have 3 possible conditions for the initial population.

It can be increasing (birth rate > mortality rate).

It can be decreasing (birth rate < mortality rate).

It can also be stable (birth rate = mortality rate).

 

2 of these have an obvious answer. If the population was increasing it will increase faster if the mortality rate is lowered. If the population was stable it will increase if the mortality rate is lowered.

 

The third initial condition that the population is initially decreasing (birth rate < mortality rate) is trickier because in this case what we know for sure is that the decrease in population will go down as the mortality rate is lowered. Now it might go down to where the birth and mortality rates are equal so the population decrease will go to zero which is another way of saying the population size becomes stable or it might go down to where the mortality rate is now less than the birth rate so that the population is now increasing as you mentioned, or it might just go down to where the mortality rate is still greater than the birth rate so the population will still be decreasing, but it will be decreasing more slowly.

Answer 2

Assuming all other population variables remain constant (ie immigration, emigration etc) and assuming that the birth rate is not zero, your thinking is correct.

 

A decrease in mortality means that people are living longer and dying at a reduced rate. If the birth rate is nonzero then new members of the population are being added every day/month/year etc. That causes the population to grow. The only factor decreasing the population is mortality, which you state is lowered. The rate of adding new people remains the same while the rate of "subtracting" people drops - so therefore the population must increase.

 

If the birth rate remains constant at zero (ie, if this is a trick question) then the population would not increase - it would continue to decrease but at a slower rate of decrease.