Mortality and _________ contribute to a decrease in population density.

Explanation

To solve the question "Mortality and _________ contribute to a decrease in population density," we need to identify the factors that lead to a reduction in population density.

### Step-by-Step Solution:

1. **Understanding Mortality**:
- Mortality refers to the death rate within a population. When individuals die, the number of organisms in that population decreases, leading to a lower population density.

2. **Identifying Other Factors**:
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