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 determine which parameters are responsible for increasing and decreasing the size of a population, we can analyze the key terms involved:

### Step-by-Step Solution:

1. **Understanding Population Dynamics**:
- Population size is influenced by various factors that can either increase or decrease it.

2. **Identifying Key Terms**:
- **Natality**: This refers to the number of births in a population over a specific time period. Higher natality contributes to an increase in population size.
- **Mortality**: This is the number of deaths in a population during a given time period. Higher mortality contributes to a decrease in population size.
- **Immigration**: This is the arrival of individuals from other areas into a population. Immigration increases the population size.
- **Emigration**: This refers to individuals leaving a population to settle elsewhere. Emigration decreases the population size.

3. **Analyzing the Options**:
- **Option A (Natality and Mortality)**: This option includes one factor that increases population (Natality) and one that decreases it (Mortality).
- **Option B (Mortality and Natality)**: This is essentially the same as Option A, just reversed.
- **Option C (Natality + Immigration and Mortality + Emigration)**: This option correctly identifies factors that increase (Natality + Immigration) and decrease (Mortality + Emigration) population size.
- **Option D (Natality + Immigration and Mortality + Immigration)**: This option incorrectly repeats Immigration, which does not contribute to a decrease in population.

4. **Conclusion**:
- The correct answer is **Option C**: Natality + Immigration (which increase population size) and Mortality + Emigration (which decrease population size).

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