Chapter 4, Problem 32A

Summary Introduction

To analyze:

The reason for population growth not stopping immediately when ZPG is reached.

Introduction:

ZPG or zero population growth is the condition when a population neither declines nor grows. It is the situation when the immigration plus birth rate equals the emigration rate plus death rate in the population. The population is thus said to be in equilibrium with approximately equal number of individuals in all, pre-reproductive, reproductive, and post-reproductive ages.

Explanation of Solution

When a population reaches ZPG, there are still slightly more number of individuals in pre-reproductive and reproductive age as the population must be previously in growing state. When shifting from growing state, the population still grows for some time till the number of individuals of all the reproductive age groups become approximately equal.

Also, if more people are immigrating in the population as those that are emigrating, the population will still grow. This is because there will be more number of individuals getting added to the population than getting subtracted.

Conclusion

The population won’t stop growing immediately when ZPG is reached because as shifting from the state of growing population, there will be more number of individuals in pre-reproductive and reproductive age. Also in instances where rate of immigration exceeds emigration, there will be slight growth in the population.