Which of the following parameters are responsible for increasing and decreasing the size of the population ?

Options

A. natality and mortality
B. mortality and natality
C. natality + immigration and mortality + emigration
D. natality + emigration and mortality + immigration

Answer

To solve the question regarding the parameters responsible for increasing and decreasing the size of a population, we will analyze the terms provided in the options and their effects on population dynamics.

### Step-by-Step Solution:

1. **Understanding the Terms**:
- **Natality**: This refers to the birth rate of a population. An increase in natality means more individuals are being born, which contributes to population growth.
- **Mortality**: This refers to the death rate of a population. An increase in mortality means more individuals are dying, which contributes to population decline.
- **Immigration**: This is the movement of individuals into a population from outside. An increase in immigration adds to the population size.
- **Emigration**: This is the movement of individuals out of a population. An increase in emigration reduces the population size.

2. **Analyzing the Options**:
- **Option 1**: Natality and Mortality - This option only considers birth and death rates, which alone do not account for the movement of individuals into or out of the population.
- **Option 2**: Mortality and Natality - This is the same as Option 1, just in a different order, and does not include immigration or emigration.
- **Option 3**: Natality plus Immigration and Mortality plus Emigration - This option correctly identifies that natality and immigration contribute to population growth, while mortality and emigration contribute to population decline.
- **Option 4**: Natality plus Immigration and Mortality plus Immigration - This option incorrectly states that both mortality and immigration contribute to population growth, which is not true.

3. **Conclusion**:
- The correct answer is **Option 3**: Natality plus Immigration (increases population) and Mortality plus Emigration (decreases population).

### Final Answer:
**Option 3: Natality plus Immigration and Mortality plus Emigration.**