Activity 3: Do Spiders Significantly Reduce Prey Population Numbers? -Class Experiment
As a class, students will be considering the question: do spiders significantly reduce prey population numbers? Have them write a hypothesis. Students can use their spiders to study this question. They should keep a list of everything their spider eats including the date, the type of food, and the amount of food. They should pool their data to reach some conclusions about the number of insects spiders eat.
The students then conduct a field study to determine the abundance of spiders in a given area. The activity requires a "study site" and at least two class days, separated by a 2-3 day break. One day is needed to catch and mark "wild" spiders and a second day to recapture them. Fortunately spiders are common and are found almost everywhere. A study site could be a hallway with lockers, a wall, a landscaped area on campus, etc. Check ahead of time to see how many spiders are quickly found. Decide if all classes will use the same site or if different sites will be used with each class.
Students will be comparing the number of spiders they capture both times with the number of new and marked spiders they capture on the second day. They can use these numbers to estimate the population size of spiders in their study site. Scientists use this technique to obtain a population count when it is impossible or impractical to capture and count all individuals.
Pool class data for each class. Use this to calculate prey numbers eaten for each study site. For the feeding rate use the data students have been collecting with their spiders in class or use the generally accepted one insect per spider per day as cited from the reading references materials for the teacher. Later combine data from all classes for a grand total.
Other questions you may wish to discuss as a class:
Activity 4: Home Study (optional)
Survey an area at home to determine the number of spiders there. Using our calculation of prey intake from class, determine the number of prey eaten.
The University of Arizona
Department of Biochemistry and Molecular Biophysics
General Biology Program for Secondary Teachers