Answer: You can see if the graphs of the two populations meet at a given point.
Explanation:
If we have a graph of population vs time
such that y = population and x = time, two different populations will be exactly the same for a given time if we have an intersection of the two graphs. The value (x0, y0) where the graphs cross is the time = x0 and the population y0, this means that both populations have y0 individuals at the same time.