Economic analysis of the effects of caloric alternatives and reinforcer magnitude on "demand" for food in baboons.

In a study examining "demand" for food, the responses of six adult male baboons (Papio c. anubis) were maintained under a fixed ratio schedule of food reinforcement during daily 22-h experimental sessions. Completion of the ratio requirement resulted in the delivery of a single 1-g food pellet. Caloric intake was studied under four food-access conditions: a single source of 1-g food pellets, two sources of pellets with different response costs, one source of pellets and one source of dextrose solutions with different response costs, or a single source of multiple pellets. Total daily caloric intake under minimal response-cost conditions did not vary across these four conditions. Increasing the response requirement for a single pellet decreased daily food intake. Compared to this single-pellet condition, increasing the response requirement: (a) decreased intake of multiple pellets to a much smaller extent; (b) decreased pellet intake to a larger extent when dextrose was available on an alternate lever and (c) decreased pellet intake to the greatest extent when pellets were available on an alternate lever. Changes in pellet intake were fitted to a theoretical equation derived by Hursh et al. (1988) to describe changes in demand for a commodity. Increasing the number of pellets per delivery decreased the rate of change in intake as cost increased, indicating decreased elasticity. Dextrose availability increased the rate of change in intake as cost increased, indicating increased elasticity. Availability of an identical food source increased the initial slope of intake without effecting the rate of change, thus also increasing elasticity. Mathematical analysis of demand curves provide a means of comparing the effects of diverse environmental manipulations on feeding behavior.