Stimulating Predator-Prey Interactions
Overview:
A predator (a blindfolded participant) hunts for prey (pieces of paper). This stimulates a
number of real situations, including for example a wading bird probing a beach for
invertebrates in the face of rising tide. The purpose is to determine and interpret the
relationship between prey density and number of prey taken by the predator which is
known as the functional response. The simulation can be modified to explore the effects
of changes in predator behavior and prey distribution on the shape of the functional
response curve.
Procedure:
Each group of students (2 or 3) should receive 50 pieces of 7 cm2 pieces of paper, a
blindfold, and a watch to keep time. One person in the group should be
designated as the predator. Five trials will be run. Each trial will be done with a
different prey density (5, 10, 15, 20, and 25). It is vital that both the prey
densities and the position of the papers on the table surface be randomized. This
will control for the possible effect of predator learning.
Blindfold the designated predator. Other members of the group randomly spread the prey
on the table top (number varies per prey density chosen). The blindfolded
predator should begin searching by tapping with the fingers of one hand on the
surface of the table to locate the prey. Sliding the fingers or palms over the
surface rapidly to sweep up the prey is cheating! The aim is to capture as many
prey as possible in 2 minutes. Once encountered, each prey is captured, killed,
and eaten by picking up the paper, folding it into quarters and dropping it into the
stomach (group member’s cupped hands). The predator resumes the search.
When the time is up the number of prey eaten is recorded, the prey for the next
trial are positioned, and the procedure is repeated until all prey densities have
been investigated.
Graph your results. The number of prey eaten is plotted against prey density. (prey
density is the vertical axis and prey eaten/unit of time is the horizontal axis).
Draw the curve. Participants will be asked to explain the shape of the curve.
Source: Investigating Biology in the Laboratory, pp. 94-99, National Association of
Biology Teachers, Reston, VA
Based on an original activity by M.C. Calver and R.D. Wooler