Impulsiveness without discounting: the ecological rationality hypothesis

Abstract

Observed animal impulsiveness challenges ideas from foraging theory about the fitness value of food rewards, and may play a role in important behavioural phenomena such as cooperation and addiction. Behavioural ecologists usually invoke temporal discounting to explain the evolution of animal impulsiveness. According to the discounting hypothesis, delay reduces the fitness value of the delayed food. We develop an alternative model for the evolution of impulsiveness that does not require discounting. We show that impulsive or short-sighted rules can maximize long-term rates of food intake. The advantages of impulsive rules come from two sources. First, naturally occurring choices have a foreground-background structure that reduces the long-term cost of impulsiveness. Second, impulsive rules have a discrimination advantage because they tend to compare smaller quantities. Discounting contributes little to this result. Although we find that impulsive rules are optimal in a simple foreground-background choice situation in the absence of discounting, in contrast we do not find comparable impulsiveness in binary choice situations even when there is strong discounting.

Time discounting and time preference in animals: A critical review

“…The disjunction between the observed discount factors and the fundamental facts of foraging behavior has been particularly salient to field biologists, ethologists, and foraging theorists, because they are in the habit of thinking in evolutionary terms (Kacelnik, 2003;Pavlic & Passino, 2010;Stephens & Anderson, 2001;Stephens, Kerr, & Fernández-Juricic, 2004). Because severe discounting ought to be strongly disfavored by natural selection, they are reluctant to accept at face value the notion that animals make such obviously poor choices in their daily lives.…”

“…Despite the pedigree of this idea, it seems unlikely that interruption risk plays a major role in laboratory intertemporal choice tasks. First, it is implausible to imagine much interruption risk in the very small number of seconds associated with discounting in most laboratory experiments (Henly et al, 2007;Stephens & Anderson, 2001;Stephens et al, 2004). Second, empirical testing of this idea has marshaled evidence opposing it (Henly et al, 2007).…”

Subjective costs drive overly patient foraging strategies in rats on an intertemporal foraging task

“…In certain situations, both humans and other animals commit to options that will only be realized long in the future, whereas in other settings, delay seems to erode value much more quickly (2)(3)(4)(5). A large body of work has demonstrated that, when choosing between reinforcers of approximately equal magnitude, decision makers often prefer immediate to delayed outcomes (6)(7)(8)(9). However, the fundamental question of how subjects compute the trade-off between the delay and magnitude of a given option remains poorly understood.…”

Sampling and tracking a changing environment: persistence and reward in the foraging decisions of bumblebees

“…If we follow the general ideas of ecological rationality, we would expect such rules to work well in the natural environments in which bees forage (e.g. [66,67]). Thus, near complete unpredictability, such as in our q ¼ 0.60 treatment, might for instance show a failure of such a rule.…”