Define zero population growth.

Explanation

**Step-by-Step Solution:**

1. **Understanding Population Growth**: Population growth is not a constant; it changes over time due to various factors such as food availability, predation, and environmental conditions.

2. **Key Factors Influencing Population Growth**: The two primary factors that influence population growth are:
- **Natality**: This refers to the number of births in a population. An increase in natality leads to an increase in population size.
- **Mortality**: This refers to the number of deaths in a population. An increase in mortality leads to a decrease in population size.

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