t can be difficult to determine the exact size of wild animal populations. This is why biologists use a variety of sampling strategies to estimate the size of populations in an area. Mobile animal populations can be estimated by using the mark and recapture method. This method involves tagging, marking, or banding the animals being studied. Like the transect and quadrat methods of sampling, the mark and recapture method uses random sampling procedures. Care must be taken to ensure that randomness occurs when the sampling is performed; otherwise, erroneous population estimates will result. Biologists can then determine, by repeating sampling procedures over time, whether a population is growing or declining. Materials You will need an opaque jar or coffee can with a lid, about 14 cup of uncooked white rice grains, a felt-tipped marker, and a calculator. Procedure 1. In this exercise, the 14 cup (50 mL or 55 grams) of white rice represents an animal population. You do not know how many grains of rice are in this measured amount of rice, just as you would not know the size of the wild population of animals that was being studied in a particular habitat. Place all the rice in