Which factors 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

Explanation

To determine the factors that would necessarily decrease the density of a population in a given habitat, we can analyze the situation step by step.

### Step-by-Step Solution:

1. **Understanding Population Density**:
- Population density refers to the number of individuals of a species per unit area in a habitat. It is calculated by dividing the total number of individuals by the area they occupy.

2. **Identifying Factors that Decrease Density**:
- To decrease the density of a population, we need to consider factors that lead to a reduction in the number of individuals in that population.

3. **Factor 1: Immigration**:
- Immigration is the process where individuals leave a population to settle in another area. When individuals migrate out, the total number of individuals in the original population decreases, leading to a lower population density.
- Example: If a population has 10 individuals and 2 individuals emigrate, the new population size is 8, thus decreasing the density.

4. **Factor 2: Mortality (Death)**:
- Mortality refers to the death of individuals within a population. An increase in mortality rates will lead to a decrease in the total number of individuals in the population.
- Example: If a population of 10 individuals experiences 3 deaths, the new population size is 7, which also results in a decreased density.

5. **Conclusion**:
- The two primary factors that would necessarily decrease the density of a population in a given habitat are immigration (individuals leaving the population) and mortality (deaths within the population).

### Final Answer:
The factors that would necessarily decrease the density of a population in a given habitat are:
1. Immigration (individuals moving out of the population).
2. Mortality (deaths occurring within the population).