Gather all your data on the objects of your study. In the case of a study on animal populations, these would be the sightings of the animals being studied in the area being concentrated on. You will also need the same data from the same area from a previous study for the purpose of making a comparison, since a single set of numbers tells you nothing about population trends.
Draw out on paper the structure of your graph. Place the names of the animals in a line along the bottom edge of your graph, and then draw a straight line above these across the page. Then create a set of incremental numbers running up the left side of the graph. These increments can be in actual numbers, or percentages.
Use the data you have gathered to draw on a blue line for each animal that matches the numbers on the left. Then repeat this using the data from the previous study, but use a different color. At the bottom of the graph, create a color code legend to show which study is represented by which color. Save your work.