Experimental technique: Testing the hypothesis of competitive exclusion Connell observed that each spring, larval stages of both Balanus and Chthamalus settled onto rocks in the lower intertidal zone and developed into early adult stages with hard shells. However, by the end of each summer, only Balanus adults remained on the rocks in the lower intertidal zone. Based on these observations, Connell made this hypothesis: Chthamalus adults are competitively excluded from the lower intertidal zone through their interactions with neighboring Balanus adults. Connell tested his hypothesis using a four-step protocol. Step 3 is particularly important in setting up the experimental and control groups in his experiment. Which of the following choices would be the most logical third step in Connell's experimental procedure, permitting him to either accept or reject his hypothesis of competitive exclusion?