A simple graphical technique for displaying individual fertility data and cohort survival: Case study of 1000 mediterranean fruit fly females

Abstract

1. A graphic technique is presented in which data on age-specific reproduction of individuals are portrayed using: (i) a horizontal life line, the length of which is proportional to individual longevity; (ii) colour-coded segments depicting the level of reproduction at each age; and (iii) a cohort survival schedule created by rank-ordering individual life lines from shortest- to longest-lived. 2. The resulting graphic, referred to as an event history diagram, portrays data at the individual level and thus allows visual comparisons of detailed life-history patterns such as age of first reproduction, longevity, ages of high, medium, low and zero reproduction, and post-reproductive period. 3. Example graphs are shown for reproductive and longevity data gathered on 1000 medfly females. The average female lived 35.6 days and laid 759.3 eggs and therefore the graphs display information for 35 600 fly days and the age-distribution of laying for 759 300 eggs. 4. Because the graphics provide a means for visualizing large amounts of data precisely and efficiently, they reveal details and nuances in the data that are not apparent from conventional graphic methods. 5. The advantages of longitudinal data gathered on individuals and reasons why visualizing individual-level data is important are discussed.