The present paper reviews studies of frequency-dependent predation in which predators tend to feed on common prey rather than rare one. This feeding pattern has been observed in a wide variety of species from protozoa to humans. Models of frequency-dependent predation have been proposed by biologists and one of these models proposed by Elton and Greenwood is mathematically similar to the generalized matching law developed in psychology. A modified version of the generalized matching law, replacing the obtained reinforcer frequency ratios with the programmed reinforcer frequency ratios, can handle the strength of the observed feeding pattern. While biologists have not attempted systematically to find factors affecting frequency-dependent predation in the wild, laboratory simulation of foraging behavior based on operant conditioning has been successfully applied to examine several factors thought to influence frequency-dependent predation, such as prey frequency, profitability, and conspicuousness. Studies with pigeons as subjects have suggested that frequency-dependent predation is affected by prey conspicuousness as well as prey profitability.

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In order to examine the role of the hippocampus in use of spatial information, fimbria-fornix lesioned (FF) rats and control rats were trained for the place learning tasks in a Morris water maze. In experiment 1, FF rats were impaired in the retention of the task in which extra-maze stimuli were available, but control rats were not. In experiment 2, the water maze was enclosed by curtains, and two objects of different appearance were hung on the water surface as intra-maze stimuli. The hidden platform was distant from the two objects, but the spatial relationship of the platform and two objects was kept constant in the pool throughout the training. The performance of the FF rats was inferior to that of control rats, although they could solve this task using only response strategy. Control rats could solve the task using both the spatial information in the maze (the place strategy) and the response strategy. These results indicated that the hippocampus plays an important role in using the spatial relationship among available stimuli, whether extra-maze (distal) stimuli or intra-maze (proximal) stimuli.

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The present study investigated the effect of MK-801 on openfield activities and object exploratory behavior in a circular openfield by using Sprague-Dawley rats. In Experiment 1, when a novel object was placed in a central zone (CZ) of the openfield, CZ-stay-time and CZ-stay-time-per-entry significantly increased, and no sex difference was shown for object exploratory behavior. In Experiment 2, MK-801 (0.05, 0.1, 0.2 mg/kg) was administered i.p.. Marked dose-dependent sex difference in object exploratory behavior and openfield activities. CZ-stay-time, CZ-stay-time-per-entry, locomotion, rearing, and leaning of males were affected by 0.1 and 0.2 mg/kg of MK-801. Females given 0.05 mg/kg of MK-801, which did not affect locomotion in males, displayed hyperactivity, and those given 0.2 mg/kg a significant reduction of activity. Females, 0.1 and 0.2 mg/kg of MK-801 affected object exploratory behavior, locomotion, rearing and leaning even on the next day of administration. These results suggested that the effect of MK-801 in female rats tends to be longer than in males, and that females are more susceptible to non-competitive NMDA receptor blockade than males.

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Photoperiodic response to a short photoperiod (SP, LD 8 : 16) was reported in Mongolian gerbils (Meriones unguiculatus). The change of testicular and epididymal weight as well as body weight was measured as a function of SP exposure of LD 8 : 16. The present findings demonstrated that Mongolian gerbils could discriminate between a long photoperiod (LP, LD 16 : 8) and a short photoperiod (SP, LD 8 : 16). Their testes as well as epididymides regressed and spontaneously redeveloped under SP exposure. Mongolian gerbils were determined from the present findings to be classified as a photoperiodic species.

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A naive rat (an observer) that interacts with a recently fed conspecific (a demonstrator) subsequently exhibits an enhanced preference for whatever food its demonstrator ate. In the present study, we investigated the effects of relationships between demonstrators and observers on the social induction of food preferences. Observer rats were exposed to two demonstrators that had just eaten different foods having flavors unfamiliar to observers, then subsequent preferences by the observers for these foods were tested in a choice situation. Observers preferred foods transmitted by unfamiliar demonstrators to those transmitted by familiar demonstrators and foods transmitted by subordinate demonstrators to those transmitted by dominant demonstrators. These differences were not due to differences in the duration of physical interactions between demonstrators and observers. Both observed preferences seem to be adaptive to the rats ; the first one works to broaden the diet and the second one reduces potential costs of obtaining food.

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Long-Evans rats were trained to lick saccharin solution or tap water through a drinking tube. Two experiments examined whether the burst licking rate is faster for saccharin than for water under a condition of water deprivation. In. Experiment 1 the burst rates of two of the three subjects were faster for saccharin than water. Volume per lick was smaller for saccharin. And the decreasing period of the burst rate was confirmed during the initial period of drinking. Experiment 2 investigated the effect of the distance between an opening for drinking and a spout of a tube outside the opening. The burst rates of two of three subjects were faster for saccharin. The difference of the burst rates for saccharin and water was not related to the distance between the opening and the spout.

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