Final answer:
X₁ represents the population in year 1, X₂ represents the population in year 2, and so on. This convention allows for tracking changes in population over time and making predictions about future population sizes.
Step-by-step explanation:
In population biology, X1 represents the population in year 1, X2 represents the population in year 2, and so on. This convention is used to track the changes in population over time, allowing for comparisons and analysis. By assigning specific values to each X, we can calculate growth rates, study population dynamics, and make predictions about future population sizes.