The effects of varying procurement costs on food intake in baboons.

Food intake of four adult male baboons (Papio anubis), ranging in weight from 18 to 33 kg, was monitored during daily experimental sessions lasting 22 hours. Food was available under a two-component operant schedule designed to mimic food availability in the natural ecology. The first component was a "procurement" component which consisted of pulling the manipulandum a set number of times under a fixed-ratio (FR) operant schedule. Following completion of the procurement response requirement, access to food, i.e., a meal, became available under the second "consumption" component during which each response produced a food pellet (one-gram banana-flavored pellets, 3.1 kcal/g). After a 10-minute interval in which no response occurred, the consumption component was terminated. In order to gain access to another meal, the baboon had to complete the ratio requirement of the procurement component. Increasing the ratio requirement of the procurement component from 10 to 200 had no significant effect on mean total daily intake, but significantly reduced the number of meals from 7.4 under the FR10 requirement to 3.6 under the FR200 procurement component. There were no differences among baboons in mean meal size, or intermeal-interval under each procurement requirement. Similar patterns of cumulative daily intake were observed within baboons under all ratio requirements of the procurement component, and there were few significant correlations between meal size and postmeal-interval, or premeal-interval and meal size in any baboon.