Optimal foraging theory: Prey density and travel requirements in Rattus norvegicus..

Two male Wistar hooded rats were allowed to forage for food by climbing nail ladders to a box containing prey mixed with sand (a patch) to investigate how environmental contingencies (constraints) operate to affect Ss' foraging behavior and patterns of optimal foraging. The amount of food was varied, as was the distance each patch was placed above the ground. Results show that under conditions of constant patch height and differing locations of patch densities, both Ss showed optimal usage of the patches. When travel between patches was difficult, there was greater utilization of each patch than when travel was easy, in accord with optimality theory. Under conditions of variable patch-density locations and difficult travel requirements, optimal foraging theory was congruent with the data. Under conditions of fixed patch-density locations or easy travel requirements, optimal foraging theory did not fit the data. It is concluded that the degree of optimality of behavior is governed by proximal mechanisms, and components such as sampling environmental events and travel risk must be included for an understanding of foraging behavior. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The work costs of earning food as a determinant of patch leaving.

Foraging theorists have long emphasized the role of the energy (work) costs of food items on foraging behavior. However, few experiments have measured this variable or demonstrated that animals are indeed sensitive to work costs. Experiment 1 assessed whether rats (Long-Evans) can use the work costs of food to determine whether a food patch is exhausted. Rats performed a fixed amount of work for each food item (fixed-work [FW] schedule), but food was withheld unpredictably to simulate sudden patch depletion. It was found that rats left patches only when the work costs of unsuccessful searches (giving-up work) exceeded the prevailing costs of food. The time and response costs of unsuccessful food searches (giving-up time and giving-up responses) were not predictive of patch leaving. Experiment 2 showed how rats regulated work in this paradigm by examining the exteroceptive stimuli connected with fulfilling the FW schedule. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Black-capped chickadees (Poecile atricapillus) anticipate future outcomes of foraging choices.

In 2 experiments we investigated the cognitive abilities of wild-caught black-capped chickadees (Poecile atricapillus) in future anticipation tasks. Chickadees were sensitive to anticipatory contrast effects over time horizons of 5, 10, and 30 min (Experiment 1). Chickadees also learned the order of events and anticipated that the quality of future foraging outcomes was contingent on current foraging choices. This behavior was demonstrated while foraging in a naturalistic aviary environment with a 30-min delay between the initial choice and the future outcome (Experiment 2). These results support the hypothesis that black-capped chickadees can cognitively travel in time both retrospectively and prospectively using episodic memory. This result shows the occurrence of anticipatory cognition in a noncorvid species of food-storing bird and supports the idea that cognitive time travel may have evolved in nonhuman animals in response to specific ecological selection pressures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Choice behavior of pigeons on progressive and multiple schedules: A test of optimal foraging theory.

16 pigeons were trained on a depleting progressive schedule and on a multiple schedule that produced food at 1 of 4 constant rates. Ss were then allowed to choose between the schedules presented concurrently to see if they switched from the progressive schedule to an alternate fixed component of the multiple schedule in a manner that maximized the benefit/cost ratio. The time of access to the food/number of pecks required to earn food (T/N) ratio was varied in 2 mathematically equivalent but procedurally different ways. Results reveal that the ratio group was more sensitive to the different T/N values than was the time group. For both groups, the number of reinforcers earned on the progressive schedule during choice tests was a decreasing function of the T/N value of the alternative fixed schedule. Predictions based on optimal foraging theory better approximated actual choice behavior than did those based on performance under the individual schedules. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bayesian analysis of foraging by pigeons (Columba livia).

In this article, the authors combine models of timing and Bayesian revision of information concerning patch quality to predict foraging behavior. Pigeons earned food by pecking on 2 keys (patches) in an experimental chamber. Food was primed for only 1 of the patches on each trial. There was a constant probability of finding food in a primed patch, but it accumulated only while the animals searched there. The optimal strategy was to choose the better patch first and remain for a fixed duration, thereafter alternating evenly between the patches. Pigeons were nonoptimal in 3 ways: (a) they departed too early, (b) their departure times were variable, and (c) they were biased in their choices after initial departure. The authors review various explanations of these data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats (Rattus norvegicus) modulate eating speed and vigilance to optimize food consumption: Effects of cover, circadian rhythm, food deprivation, and individual differences.

The eating behavior of rats given food pellets of specified size was examined as a function of environmental, circadian, and experiential influences. Eating times were shorter in lighted, exposed environments than in dark, covered environments, even though in novel, exposed conditions the rats made many scanning movements as they ate. Eating time also varied as a function of the circadian cycle in that eating times were shorter in the night portion of the day–night cycle. Finally, eating times decreased if rats were food deprived, and deprivation had a small but enduring influence. Within the tests there were differences in the eating times of individual rats that were not attributable to the experimental manipulations. That rats can optimize food intake by varying eating speed is discussed in relation to physiological regulation of feeding and to optimal foraging theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feeding diversity in deer mice.

Compared the foraging behavior of 2 geographically isolated subspecies of deer mice. Laboratory-reared Peromyscus maniculatus borealis from the prairies of Alberta, Canada and P. m. blandus from the deserts of Arizona were studied in 3 tests emphasizing different aspects of foraging: approach, acquisition, and consumption. Two measures were used to compare feeding: diversity, an index of the breadth of the diet, and preference, an index of what Ss ate most. A consistent difference found between the 2 subspecies in individuals' feeding diversity suggests that this subspecific effect is due to genetic differences, as predicted by evolutionary theory. At the same time that individuals of each subspecies had roughly the same diversity, they had different preferences, which suggests that they are more variable or opportunistic in their foraging choices than predicted by theories of optimal foraging. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tracking and averaging in variable environments: A transition rule.

Sprague-Dawley rats were exposed to variable patches in 2 controlled laboratory settings where duration and magnitude of yield were systematically varied along with the time intervening between foraging experiences and choice tests. Following relatively short delays, rats chose the patch that was best at the end regardless of its average value. However, as delays lengthened, rats chose the patch with the best average irrespective of its final performance. Despite widely differing procedures, preference shifts were an orderly function of time and patch quality and were predicted with precision by the temporal weighting rule (TWR), a biologically based quantitative model that discounts patch outcomes as a hyperbolic function of time. The laboratory phenomenon of spontaneous recovery is best understood in terms of the dynamic averaging process prescribed by TWR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Central-place foraging by Rattus norvegicus on a radial maze.

We studied central-place foraging in rats (Rattus norvegicus) by placing food items that varied in size and weight at the ends of a 4-arm radial maze. In Experiments 1–3, rats increasingly tended to carry food to the center of the maze as the size of those items increased. Very large food items often were hoarded in the center. Rats consumed food faster on the arms than in the center, and rats traveled faster when carrying food than when not. Blocking arm entrances increased travel time between the center and the arms and decreased food carrying at every item weight except the largest. In Experiments 4–6, important conditions that influence the degree of food-carrying behavior were discovered; these were the intersection of maze arms, the presence of a conspecific, and the use of open vs. closed maze arms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time-dependent decisions in dogs (Canis familiaris).

Investigated whether the foraging decisions of dogs (Canis familiaris) were time dependent and consistent with a temporal weighting rule (TWR) for maximizing the reliability of information. Dogs were given information about patches whose qualities varied over time. To stimulate natural conditions, interruptions at selected points in foraging were interposed. Patch choices were time dependent and closely matched the predictions of the TWR. Dogs relied on very recent information when available, but with increasing delays they used patch averages. The TWR may be a general solution to problems faced by foragers in variable environments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactions between the prefrontal cortex and amygdala during delay discounting and reversal.

Interactions between the prefrontal cortex and amygdala are thought to be critical for reward anticipation. Alterations in reward anticipation that lead to an inability to wait for rewards or a diminished capacity to change behavior when doing so would be optimal are often termed impulsivity and compulsivity, respectively. Distinct regions of the prefrontal cortex may support decreased impulsivity through self-control and decreased compulsivity through flexibility. However, both self-control and flexibility appear to involve the amygdala. Using a delay discounting paradigm, the current investigation found that inactivation and disconnection of the medial prefrontal cortex and basolateral amygdala led rats to become more impulsive by affecting preference for smaller immediate over larger delayed rewards. Conversely, inactivation and disconnection of the orbitofrontal cortex and amygdala led rats to become more compulsive as demonstrated by an inability to flexibly reverse stimulus–reward relationships in an odor reversal task. The current findings support a double dissociation between orbitofrontal cortex–amygdala interactions for odor reversal and medial prefrontal cortex–amygdala interactions for delay discounting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats with fimbria-fornix lesions are impaired in path integration: a role for the hippocampus in "sense of direction"

Animals can locate their present position in relation to a starting point and return to that starting point using cues generated by self-movement, a navigation strategy called dead-reckoning. Because contemporary research on spatial navigation suggests that some aspects of spatial navigation depend on the integrity of the hippocampal formation, whereas others do not, the present study examined whether dead-reckoning is hippocampally dependent. The task capitalized on the proclivity of foraging rats to carry large food pellets to a shelter for eating. Control rats and rats with fimbria-fornix (FF) lesions left a hidden burrow to search for one piece of food located somewhere on a circular table. The accuracy with which they returned to the burrow with the food was measured. In three experiments, rats received probe trials in which they (1) started from novel locations, (2) wore blindfolds to obscure visual cues, and (3) foraged under a condition in which surface cues, e.g., odors left by their outward searches, were displaced. Both sighted control and FF rats preferentially used visual cues for guidance when foraging from a familiar location. Control rats were accurate and FF rats were impaired in returning to novel starting locations (1) when sighted, (2) when blindfolded, and (3) when blindfolded in tests in which surface cues were displaced. These results, as well as detailed observations on the behavior of the animals, are consistent with the hypothesis that rats can use dead-reckoning to solve spatial problems, and this ability depends on the integrity of the hippocampal formation.     

RAGE mRNA expression in the diabetic mouse kidney

Data are accumulating that insulin acting in the central nervous system is a physiological regulator of food intake and body weight, presumably via its effect in the hypothalamus. The present study investigated whether infusion of a small dose of insulin into two major hypothalamic insulin-binding areas also has an effect on diet selection and behavior. At the beginning of the dark period, rats received local bilateral infusions of 4 microU of insulin or vehicle during 34 min into the arcuate (ARC) or paraventricular (PVN) nucleus of the hypothalamus. Consumption of carbohydrate (C)-, protein (P)-, and fat (F)-enriched food and time spent on certain behaviors (drinking, resting, grooming, rearing, exploring/sniffing) were assessed during the first nocturnal hour. In addition, 21-h diet selection was assessed. The percentage contribution of macronutrients (C/P/F) to total energy content of the C-, P-, and F-enriched diets was 71.9/17.2/10.9, 45.8/43.4/10.8, and 47.1/17.5/35.4, respectively. During the first hour, infusion of insulin into the PVN increased grooming behavior compared to infusion of the vehicle. Although infusion of insulin had no effect on diet selection during the first hour, insulin infused in the ARC caused a reduction in F-enriched food consumption and total intake of F (as a macronutrient) over the 21-h period without altering total food intake. Infusion of a higher dose of insulin (10 microU) into the third ventricle had no effect on any of the assessed parameters. The data are explained to indicate that insulin (being an indicator of a positive energy balance) adjusts body weight homeostasis by modulating the preference for fat, at least at the level of the ARC, but not at the PVN.     

Conditional copying fidelity in capuchin monkeys (Cebus apella).

In the last two decades, it became largely accepted that monkeys show little, if any, copying fidelity. However, some recent studies have begun to challenge this notion. To explore reasons for such contrary findings, we designed a foraging apparatus so that in each of two experiments with capuchin monkeys (Cebus apella), a model would demonstrate one of two alternative methods to obtain food. The apparatus had a V-shaped track on which a panel could be slid up left or right from the center to reveal food. In Experiment 1, food was located in a cup directly behind the center panel. In Experiment 2, sliding the panel left or right revealed food either in left or right ends of the V-track. Since this sliding movement led directly to one food location exclusive of the other, we predicted capuchins would show greater copying fidelity in this second Experiment. Instead, subjects were significantly more faithful to the model’s method in Experiment 1, which provided strong evidence of capuchins copying what they had observed. We suggest that the contrasting results of Experiment 1 may have occurred because capuchins prioritize exploratory behavior when alternative foraging locations are accessible. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anticipatory cues can interfere with inhibitory operant behavior in the rat

In four separate experiments a total of 24 male rats were trained for 30 min. daily in the same temporal order to inhibit their responses for at least 6 sec. before a response-contingent reward was delivered (DRL-6 sec.). The rats tested as the second group each day displayed about twice the number of errors (effect size = 40%) shown by rats tested in the first or third groups. These results suggest that anticipatory cues, acquired within two sessions, interfere with response inhibition during an appetitive task for a limited time (between a few minutes to about one hour). The results are consistent with the hypothesis that learned anticipation of reward may decrease inhibitory mechanisms by facilitating limbic lability.     

Foraging and spatial memory in pigeons (Columba livia).

In two experiments pigeons were studied as they foraged through a simulated patchy environment. Patches consisted of four circular groupings of feeders placed at different locations within a laboratory room. The properties of these patches varied between experiments. In Experiment 1 all feeders in all patches were baited, but the number of food pellets per feeder varied between patches. In Experiment 2 density of food was varied between patches, with 25%, 50%, 75%, or 100% of the feeders randomly baited. A number of variables that indicated pigeons' patch preferences and their behavior within patches were measured. Pigeons showed strong initial preferences for patches containing larger numbers of pellets per feeder in Experiment 1 but did not show differential preferences for patches varying in food density in Experiment 2. Within patches pigeons visited more feeders in richer patches than in poorer patches, both on initial patch entry and on repeat visits. Although pigeons showed evidence of reference and working spatial memory for patches, both experiments failed to provide evidence for the use of working spatial memory for the positions of visited and unvisited feeders within patches. The implications of these findings for spatial memory and foraging theory are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Animals foraging in the lab: Problems and promises.

Foraging has become a popular catchword in literature like that published in this Journal. Several different kinds of psychological research on foraging can be distinguished. These include tests of optimal foraging models using operant schedules and other simulations, analyses of the mechanisms assumed as constraints in optimality models, tests of the optimality of behavior on arbitrary schedules, and use of seminaturalistic laboratory situations. This kind of work is not without problems. One is that the gap between "real" and simulated foraging has been insufficiently explored. More important, accounts of behavior in terms of function (e.g., optimal foraging theory) are often confused with those in terms of mechanisms of learning, memory, and choice. The most productive research strategy in this area is to juxtapose predictions of functional and mechanistic models and attempt to understand any differences between them. Studies of foraging behavior can also reveal new or poorly studied phenomena. Because optimal foraging theory makes ideas about function explicit and precise, well-formulated investigations of foraging behavior can contribute substantially to understanding learning, memory, and decision processes as biological adaptations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The rat's anticipation of two meals a day.

Studied anticipation behavior of 12 female rats that were maintained on 2 meals a day, at 10:00 AM and 4:00 PM, for 1 mo while confined to activity wheels. During this time the Ss developed anticipatory running, i.e., increased activity just prior to each meal. Because the anticipation effect was found in Ss with minimal weight loss, it is interpreted as an incentive-motivation effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A naturalistic investigation of eating behavior in bulimia nervosa.

This study investigated the parameters of eating behavior in subjects meeting the diagnosis of bulimia nervosa (BN). Twenty BN and 24 female comparison (FC) subjects monitored hourly over a number of consecutive days their food intake, mood, hunger, social circumstances, and experiences of unpleasant events. Compared with FC subjects, BN subjects reported more positive moods relative to their typical moods in the hour prior to consuming a meal. Within the BN group, subjects reported more negative moods in the hour prior to a binge episode compared with their moods prior to consuming a snack or meal. The BN subjects were also calorie deprived in the hour prior to a binge episode relative to FC subjects at an equivalent time of the day. These results are discussed within the framework of restraint theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Creeping dispositionism: The temporal dynamics of behavior prediction.

Four studies tested the hypothesis that temporal distance increases the weight of global dispositions in predicting and explaining future behavior. Study 1 found that the correspondence bias was manifested more strongly in predictions of distant future behavior than of near future behavior. Study 2 found that participants predicted higher cross-situational consistency in distant future behavior than in near future behavior. Study 3 found that participants sought information about others' more global dispositions for predicting distant future than near future behavior. Finally, Study 4 found that participants made more global causal attributions for distant future outcomes than for near future outcomes. The results were interpreted as supporting the assumption of construal level theory that perceivers use more abstract representations (higher level construals) to predict and explain more distant future behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)