Economic theory predicts that cost is an inverse function of the quantity of a commodity. This has also been shown in studies of behavioral economics (Dougan, 1992). According to the law of supply and demand, competition between organisms should drive prices up more rapidly. Previous studies with rats have failed to find an effect of competition; however, the competition was indirect in those studies (Johns, unpublished thesis). In the present experiment, twelve female rats actively competed in pairs for reinforcers on each of four modified fixed interval (FI) schedules: FI 30 s, FI 60 s, FI 120 s, and FI 240 s. A modified operant chamber was used and the animals were separated by a wire barrier. For each schedule, the animals were tested both with and without competition from another rat. Competition involved a pair of animals responding on separate bars where only one would receive reinforcement on a given trial. The non-competition days served as controls. As predicted by the law of supply and demand, the competition resulted in increased cost. The results have a variety of implications for schedule behavior in general and behavioral economics in particular.



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