Which of the following would necessarily decrease the density of a population in a given habitat ?

Options

A. Natality gt mortality
B. Immigration gt emigration
C. Mortality and emigration
D. Natality and immigration

Answer

To determine which factors would necessarily decrease the density of a population in a given habitat, we need to understand the concept of population density and the factors that affect it.

### Step-by-Step Solution:

1. **Define Population Density**:
- Population density is defined as the number of individuals of a species per unit area. It is a measure of how crowded a population is in a specific habitat.

2. **Identify Factors Increasing Population Density**:
- There are two main factors that can increase the density of a population:
- **Natality (Birth Rate)**: The birth of new individuals increases the population size.
- **Immigration**: The arrival of individuals from other populations also increases the population size.

3. **Identify Factors Decreasing Population Density**:
- Conversely, there are two main factors that can decrease the density of a population:
- **Mortality (Death Rate)**: The death of individuals reduces the population size.
- **Emigration**: The departure of individuals from the population reduces the population size.

4. **Conclusion**:
- To answer the question, we need to identify which of the options provided would necessarily lead to a decrease in population density. The factors that do this are mortality and emigration.

5. **Final Answer**:
- Therefore, the correct answer is that factors such as mortality and emigration would necessarily decrease the density of a population in a given habitat.