Mathis, C. E., Johnson, D. F., & Collier, G. (1996).
Food and water intake as functions of resource consumption costs in a closed economy.
Journal of the Experimental Analysis of Behavior,
65, 527-547.
In two experiments, rats living in a closed economy were offered
continuous, concurrent access to four resources: food, water, a
nest, and a running wheel. Costs of consuming food and water were
imposed with bar-press requirements, and the price of either one
or both resources was raised. As the consumption cost increased,
less was consumed in each bout of resource use. Bout frequency
increased, but not sufficiently to compensate for the fall in
bout size, and total intake fell. Food and water tended to be
complementary resources, in that as intake of one fell with its
price, intake of the other also decreased. This interaction was
accounted for by the defense of the ratio of body water to lean
body mass. As amount consumed decreased, increases in feed
efficiency (weight gain per unit of food ingested) and the use of
stored calories compensated for the reduced energy intake. There
was evidence of competition between feeding and drinking at the
higher costs: When both commodities were expensive, the decline
in the intake of each one was greater than when only one
commodity was expensive. Although the time spent nesting,
running, and in unmonitored activity was adjusted when feeding or
drinking took more of the rat's day, there was no particular
activity that was sacrificed.
Key words: food intake, water intake, consumption cost,
fixed-ratio schedule, behavioral economics, closed
economy, lever press, rats