A RATE COMPARISON MODEL OF CONCURRENT SCHEDULE PERFORMANCE
A rate comparison model of concurrent schedule performance and foraging is proposed. The model is a molecular equalizing theory of matching, based on results from optimal foraging theory and corresponding data from behavioral ecology. It state that animals leave one concurrent alternative for another whenever their estimates of current local food rates fall below a criterion based on habitat-wide average rates. Linear operator rules are offered as among the most plausible rate estimation strategies. The model may be applicable to both schedule performance and foraging in patchy natural environments, even though differences between these situations may result in variations in how rate comparison processes are employed. The model predicts that stay times in alternatives within concurrent schedules should reveal several consistent patterns when analyzed as giving-up times, i.e., those times between the last food encounter (or entry) in an alternative and a switch. These predictions were applied to an experiment with pigeons using concurrent variable interval schedules and other schedules based on continuous responses with explicit travel requirements for switching. In agreement with predictions, giving-up times increased with decreasing overall food density, and provided evidence for strategies such as linear operator rules which incorporate rate estimation and comparison rather than simpler time-based switching rules. Giving-up times were much shorter than average interfood intervals in variable interval schedules, but closer to interfood intervals in a similar condition in which local food rates were constant, demonstrating that locally high food probabilities affect switching criteria. The chief differences between concurrent schedule results and foraging data were seen as due to the differing extents to which animals can use cues signalling the quality of alternatives in the two situations.
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