Fruit Flies. Researchers tracked a population of 1,203,646 fruit flies, counting how many died each day for 171 days. Here are three-time plots offering different views of these data. One shows the number of flies alive on each day, one the number who died that day, and the third the mortality rate—the fraction of the number alive who died. On the last day studied, the last 2 flies died, for a mortality rate of 1.0.