Residence Time and Choice in Concurrent Foraging Schedules

Abstract

Five pigeons were trained on a concurrent-schedule analogue of the "some patches are empty" procedure. Two concurrently available alternatives were arranged on a single response key and were signaled by red and green keylights. A subject could travel between these alternatives by responding on a second yellow "switching" key. Following a changeover to a patch, there was a probability (p) that a single reinforcer would be available on that alternative for a response after a time determined by the value of lambda, a probability of reinforcement per second. The overall scheduling of reinforcers on the two alternatives was arranged nonindependently, and the available alternative was switched after each reinforcer. In Part 1 of the experiment, the probabilities of reinforcement, rho(red) and rho(green), were equal on the two alternatives, and the arranged arrival rates of reinforcers, lambda(red) and lambda(green), were varied across conditions. In Part 2, the reinforcer arrival times were arranged to be equal, and the reinforcer probabilities were varied across conditions. In Part 3, both parameters were varied. The results replicated those seen in studies that have investigated time allocation in a single patch: Both response and time allocation to an alternative increased with decreasing values of lambda and with increasing values of rho, and residence times were consistently greater than those that would maximize obtained reinforcer rates. Furthermore, both response- and time-allocation ratios undermatched mean reinforcer-arrival time and reinforcer-frequency ratios.

Residence Time in Concurrent Foraging With Fixed Times to Prey Arrival

“…These ''overstaying'' results were replicated with pigeons by Davison and McCarthy (1994) and McCarthy, Voss, and Davison (1994). Jones and Davison (1996) introduced a concurrent variant of the ''some patches are empty'' procedure in which two discriminated patches were available, with potentially different times to reinforcers (preyarrival times) and different probabilities of reinforcers in the two patches. Despite the increased complexity of the task, their results closely replicated the results of Kamil et al, Davison and McCarthy, and McCarthy et al Brunner, Kacelnik, and Gibbon (1992) reported results from a modified procedure in which up to four prey items could be obtained on a single entry to a patch, each scheduled on equal successive fixed-interval (FI) schedules and terminating in a prey-absent trial.…”

“…Ϯ15 g of their ad lib body weights. The subjects were the same as those used by Jones and Davison (1996). The subjects were fed amounts of mixed grain, immediately after sessions, sufficient to maintain their designated body weights.…”

“…The apparatus was the same as used by Jones and Davison (1996). All experimental contingencies were arranged on an IBMcompatible computer, situated remote from the experimental chamber, and running MED-PC software.…”

“…Although they are presumably present, the precise effects of reinforcement for exiting are unclear in the standard ''some patches are empty'' procedure because the reinforcer parameters of future patches are the same as those arranged in the present patch, so that changes in present-and alternative-patch parameters are confounded. In contrast, the concurrent analogue of this procedure, introduced by Jones and Davison (1996), has the potential to separate the relative contributions to patch residence of both reinforcerarrival times in the present patch and arrival times following travel in alternative patches. If two patches with different reinforcer-arrival times are signaled by discriminative stimuli and arranged according to the Jones and Davison procedure, residence times in one patch may well be shortened when the arrival time in the alternative patch is made relatively short and be lengthened when the alternative arrival time is made relatively long.…”

“…The present experiment investigated residence time in a modification of the concurrent ''some patches are empty'' procedure used by Jones and Davison (1996). The purpose of the present experiment was to investigate more closely timing in patch residence by arranging fixed, rather than variable, times to reinforcers in patches.…”