Which of the following factors influence population density under normal conditions ?

Options

A. Deaths
B. Immigration
C. Emigration
D. Both (a) and (c)

Explanation

To determine which factors influence population density under normal conditions, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Population Density**:
- Population density refers to the number of individuals of a species per unit area or volume. It is a dynamic measure that can change over time due to various factors.

2. **Identifying Influencing Factors**:
- Several factors can influence population density, including:
- Availability of food
- Environmental conditions (adverse or favorable)
- Climatic conditions

3. **Key Processes Affecting Population Density**:
- The population density is primarily influenced by four key processes:
- **Birth (Natality)**: The addition of new individuals to the population.
- **Death (Mortality)**: The removal of individuals from the population.
- **Immigration**: The arrival of individuals from other populations.
- **Emigration**: The departure of individuals to other populations.

4. **Focusing on Normal Conditions**:
- Under normal conditions, the two main factors that significantly influence population density are:
- **Birth**: Increases population density as new individuals are born.
- **Death**: Decreases population density as individuals die.

5. **Role of Immigration and Emigration**:
- While immigration and emigration can affect population density, they are generally less significant under normal conditions compared to birth and death. Immigration may play a more crucial role during events like ecological succession or when a habitat is being invaded by new species.

6. **Conclusion**:
- Therefore, the primary factors influencing population density under normal conditions are **birth (natality)** and **death (mortality)**.

### Final Answer:
The factors influencing population density under normal conditions are **birth and death**.

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