Food and water intake as functions of resource consumption costs in a closed economy.
Higher response cost shrinks both food and water intake even when animals try to compensate with more frequent, smaller bouts.
01Research in Context
What this study did
The team put six rats in a closed economy.
The rats had to press a bar for every food pellet or water drop.
The scientists raised the bar-press cost every few days: 5, 20, 40, 80, 160 presses.
They watched how much the rats ate and drank over the study period.
What they found
When the bar cost went up, the rats took smaller bites and sips.
They started eating and drinking more often, but the tiny bites could not keep the totals up.
Total food and water dropped by half at the highest cost.
Food and water acted like best friends: when one went down, the other followed.
How this fits with other research
Ballard et al. (1975) showed that fewer food pellets make rats drink more after each pellet.
Cryan et al. (1996) flips that idea: when you make the pellet harder to get, both eating and drinking fall.
The difference is simple: 1975 kept the work easy and cut the payoff; 1996 kept the payoff the same and raised the work.
Castilla et al. (2013) later echoed 1975: hungry rats on fast schedules lick more.
Together the trio shows that deprivation boosts adjunctive drinking, but added response cost kills it.
Why it matters
Your client may stop eating or drinking if the response cost is too high.
Check the effort required for bites and sips in token or contingency systems.
If intake drops, lower the cost first—don’t just add more prompts.
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02At a glance
03Original abstract
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.
Journal of the experimental analysis of behavior, 1996 · doi:10.1901/jeab.1996.65-527