Among the following which causes the increase in population density?

Options

A. Natality
B. Mortality
C. Immigration
D. Both (1) and (3)

Answer

To solve the question regarding which factors cause an increase in population density, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Population Density**:
- Population density is defined as the number of individuals living per unit area. An increase in population density means that there are more individuals in a given area.

2. **Analyze the Options**:
- The options provided are:
- Option 1: Natality
- Option 2: Mortality
- Option 3: Immigration
- Option 4: Both 1 and 3

3. **Evaluate Natality**:
- Natality refers to the birth rate of a population.
- If the birth rate increases, it leads to more individuals being born, which contributes to an increase in population density.
- Therefore, **natality can cause an increase in population density**.

4. **Evaluate Mortality**:
- Mortality refers to the death rate of a population.
- An increase in the death rate would lead to a decrease in the number of individuals in the population, thereby reducing population density.
- Conversely, a decrease in mortality would allow more individuals to survive, potentially increasing population density.
- However, since we are looking for factors that directly cause an increase, **mortality does not contribute positively to an increase in population density**.

5. **Evaluate Immigration**:
- Immigration is the movement of individuals into a population.
- When individuals immigrate into a population, it increases the number of individuals in that area, thus increasing population density.
- Therefore, **immigration also causes an increase in population density**.

6. **Conclusion**:
- Based on the evaluations, both natality (birth rate) and immigration (movement into the population) contribute to an increase in population density.
- Therefore, the correct answer is **Option 4: Both 1 and 3**.

### Final Answer:
**The correct answer is: Both 1 and 3 (Natality and Immigration)**.