Acquisition, extinction and temporal discrimination in human conditioned avoidance

Two experiments were conducted with the aim of designing a videogame for the study of human conditioned avoidance. Participants had to destroy enemy spaceships with the goal of increasing the score in a counter. Coloured signals might announce the launching of a bomb that could hit participant's spaceship producing a 30 points decrease in participant's score. Three groups of participants were trained in discriminating between a warning signal (W) and a safety signal (S) in Experiment 1. Instrumental group could avoid the loss of points by hiding the spaceship before the offset of W. Participants in the Yoked group received the same treatment received by their instrumental partners, regardless of their behaviour. In the Pavlovian group, W was always followed by the loss of points, regardless of participant's behaviour. Discrimination between W and S was better in the Instrumental groups than in the Yoked and Pavlovian control groups. Experiment 2 found extinction of avoidance when the warning signal was not followed by the bomb. Temporal discrimination was found within the participants that received the instrumental contingency in both experiments, with higher avoidance response towards the end of the warning signal. Temporal discrimination disappeared after extinction in Experiment 2.     

Effects of prefeeding, extinction, and distraction during sample and comparison presentation on sensitivity to reinforcer frequency in matching to sample

The present experiment examined the effects of several test manipulations on discrimination, accuracy and sensitivity to reinforcer frequency in a conditional discrimination. Four pigeons responded on a multiple schedule of matching to sample procedures in which the reinforcer-frequency ratio for correct comparison choice responding was varied across components within session from 1:9 to 9:1. Following stability, the effects of prefeeding, extinction, and distraction during sample and comparison presentation were assessed. Discrimination accuracy decreased under prefeeding, extinction, and distraction during sample presentation. Sensitivity to reinforcer frequency decreased under prefeeding and extinction. Decreases in sensitivity were positively related to decreases in discrimination accuracy. The decreases in discrimination accuracy and sensitivity under prefeeding and extinction are interpreted as being due to decreases in attending to the sample and comparison stimuli, respectively, possibly mediated by motivational effects of these manipulations. This interpretation is consistent with current conceptualizations of the contingencies that govern conditional-discrimination performance.     

Inbreeding and extinction: Effects of rate of inbreeding

Deleterious alleles may be removed (purged) bynatural selection in populations undergoinginbreeding. However, there is controversyregarding the effectiveness of selection inreducing the risk of extinction due toinbreeding, especially in relation to the rateof inbreeding. We evaluated the effect of therate of inbreeding on reducing extinction risk,in populations of Drosophila melanogastermaintained using full-sib mating (160replicates), or at effective population sizes(N _e) of 10 (80) or 20 (80).Extinction rates in the populations maintainedusing full-sib mating occurred at lower levelsof inbreeding than in the larger populations,whereas the two larger populations did notdiffer significantly from each other.Inbreeding coefficients at 50% extinction were0.62, 0.79 and 0.77 for the full-sib (N _e = 2.6), N _e = 10 and N _e = 20 treatments, respectively. Populations of N _e = 20 that remained extant after 60 generations, showed inbreeding depression, with the mean fitness of these populations being only 45% of the outbredcontrols. There was considerable variationamong the 31 inbred populations in fitness, butnone of the N _e = 20 populations hadfitness that was higher than the outbredcontrol. We conclude that purging may slow therate of extinction slightly, but it cannot berelied on to eliminate the deleterious effectsof inbreeding.     

Effects of extinction on food web structures on an evolutionary time scale

Extinction affected food web structure in paleoecosystems. Recent theoretical studies that examined the effects of extinction intensity on food web structure on ecological time scales have considered extinction to involve episodic events, with pre-extinction food webs becoming established without dynamics. However, in terms of the paleontological time scale, food web structures are generated from feedback with repeated extinctions, because extinction frequency is affected by food web structure, and food web structure itself is a product of previous extinctions. We constructed a simulation model of changes in tri-trophic-level food webs to examine how continual extinction events affect food webs on an evolutionary time scale. We showed that under high extinction intensity (1) species diversity, especially that of consumer species, decreased; (2) the total population density at each trophic level decreased, while the densities of individual species increased; and (3) the trophic link density of the food web increased. In contrast to previous models, our results were based on an assumption of long-term food web development and are able to explain overall trends posited by empirical investigations based on fossil records.     

Manipulating pre-feed, density of reinforcement, and extinction produces disruption in the Location variation of a temporal discrimination task in pigeons

When pharmacological and non-pharmacological agents are used to disrupt temporal discrimination, two major findings have emerged in the literature. One result reveals lateral shifts of the psychophysical curve for time due to disruptors, while the other is a decrease in accuracy for classifying short and long intervals and a flattening of the psychophysical curve. These results represent a discrepancy within the timing literature that requires clarification. The current study determined the effects of pre-feed, increased density of reinforcement during session, and extinction on the Location variation of a temporal discrimination procedure. The results showed that extinction and pre-feed (at higher levels), when presented in an acute fashion, led to right-ward shifts in the psychophysical curve. Our results, when compared to similar studies in the literature, suggest that lateral shifts are more likely to be found due to disruptors when the Location variation is being used and when procedures are less complicated.     

Effects of temperature and food quality on isotopic turnover and discrimination in a cladoceran

Our experimental study was designed to assess the effects of temperature on nitrogen isotope turnover and to measure the effects of temperature and food quality on the stable carbon and nitrogen isotope discrimination factors (Δ¹³C and Δ¹⁵N) in a cladoceran. For the first part of our study, Daphnia were fed with non-enriched or ¹⁵N-enriched Scenedesmus obliquus at 12, 15, 20, and 25 °C. For the second part, Daphnia were reared at 15, 20, and 25 °C on Scenedesmus or Cryptomonas sp. There were no clear effects of temperature on turnover rates of the nitrogen isotope of cladocerans. However, a general increase in Δ¹³C with increasing temperature was measured, regardless of the food source. Δ¹⁵N was also affected by temperature, but contrasting results were measured depending on the food source used. There were significant effects of food quality on Δ¹³C and Δ¹⁵N in Daphnia, as values obtained for Daphnia fed Scenedesmus were always higher than those obtained for Daphnia fed Cryptomonas. Our experiments produced discrimination factors that were very different from those usually considered in isotope studies and showed that the values used for isotope model implementation to analyze field data need to be adapted to environmental conditions.     

Effects of food availability on temporal activity patterns and growth of Atlantic salmon

1. Patterns of sheltering and activity are of fundamental importance in the ecology of animals and in determining interactions among predators and prey. Balancing decreased mortality risk when sheltering with increased feeding rate when exposed is believed to be a key determinant of diel patterns of sheltering in many animals. 2. Despite lower foraging efficiency at night than during the day, Atlantic salmon Salmo salar parr are nocturnal during winter and at low summer temperatures. Nocturnal activity also occurs at warm water temperatures during summer, but little is known about the functional significance of this behaviour. 3. This study aimed to determine: (1) the preferred activity and shelter pattern of Atlantic salmon parr during warm summer months, and (2) their response to variations in food availability when balancing growth rate (G) and mortality risk (M), as expressed through time out of shelter. We differentiated among four potential responses to reduced food availability: (1) no response; (2) G decreases but M remains constant; (3) G remains constant but M increases; and (4) G decreases and M increases. 4. Time exposed from shelter was inversely related to food availability. Fish subject to high food availability were significantly less active during the day than those with restricted rations. However, food availability had no significant effect on the extent to which fish were active at night. There was no evidence of variation in growth rate with food availability. 5. Salmon were predominantly nocturnal at high ration levels, consistent with their previously reported behaviour during winter. Rather than switching to diurnal behaviour at high temperatures per se, as previously was supposed, it appears that the fish are diurnal only to the extent needed to sustain a growth rate, and this extent depends on food availability. 6. Atlantic salmon parr modulate the amount of time they are active rather than growth when responding to variations in food availability over an order of magnitude.     

Characterizing the effects of d-amphetamine on temporal discrimination

Although the effects of dopamine agonists on temporal discrimination have been widely studied, conclusions as to their behavioral and neurophysiological effects are difficult due to a number of discrepant findings in the literature. This study examined whether a previously unexplored procedural difference could account for some of these discrepancies. In three experiments, pigeons categorized the duration of temporal samples during two variants of the interval-bisection procedure. In the position variant, responses to a side key that corresponded to the sample duration produced food. In the color-matching variant, responses to the key color that corresponded to the sample duration produced food. Across experiments, d-amphetamine produced a general disruption of temporal discrimination not accompanied by over or underestimation of time in both procedures. This effect occurred whether pigeons were exposed to both procedures within session (Experiment 1) or across conditions (Experiments 2 and 3) and whether the pigeons were drug experienced (Experiments 1 and 2) or naïve (Experiment 3). Analyses of the cumulative normal functions fitted to the proportion-long response data indicated that d-amphetamine produced its effects by selectively decreasing stimulus control, rather than by affecting timing.     

The role of temporal generalization in a temporal discrimination task

Two experiments trained rats to discriminate two or three stimulus durations using a temporal discrimination task. A standard peak shift effect was observed when training was administered with short versus long signals in Experiment 1. Both discrimination accuracy scores and the generalization gradients revealed that shorter intervals were discriminated more accurately, which may be due to the scalar property of timing. In Experiment 2, three signals (short, medium, and long) were associated with three different responses, or two of the intervals were associated with one response (short and long or short and medium) and the other interval with a different response. Here, the short/medium versus long discrimination was learned most readily of the three tasks. The results of both experiments indicated a strong contribution of learning of individual durations combined with scalar generalization gradients, but Experiment 2 indicated that categorical encoding of durations may have also been operating.     

Spatial and temporal extinction dynamics in a freshwater cetacean

Geographical range contraction is a fundamental ecological characteristic of species population decline, but relatively little investigation has been conducted into general trends in the dynamic properties of range collapse. The Yangtze River dolphin or baiji (Lipotes vexillifer), probably the first large mammal species to have become extinct in over 50 years, was believed to have experienced major range collapse during its decline through progressive large-scale range contraction and fragmentation. This range-collapse model is challenged by a new dataset of 406 baiji last-sighting records collected from across the baiji''s historical range during an interview survey of Yangtze fishing communities. Although baiji regional abundance may have varied across its range, analyses of the extensive new sighting series provide comprehensive evidence that baiji population decline was not associated with any major contraction in geographical range across the middle–lower Yangtze drainage, even in the decade immediately before probable global extinction of the species. Extinction risk in baiji was therefore seemingly not related to evidence of range collapse. Baiji apparently underwent large-scale periodic and seasonal movements across their range, and we propose that range contraction and fragmentation may not be general biogeographic characteristics for declining populations of mobile species in connected landscapes.     

Effects of delays on human performance on a temporal discrimination procedure: evidence of a choose-short effect

Studies of temporal discrimination in non-human subjects have reliably shown a choose-short effect: higher matching accuracy on short-duration-sample trials than on long-duration-sample trials. This effect occurs as a function of increasing the delay between the onset of sample and comparison stimuli in a delayed matching-to-sample procedure. The present experiment investigated whether the choose-short effect could be demonstrated in human subjects under conditions which paralleled those used with non-human subjects. Subjects responded under a discrete-trial procedure in which they were required to push one of two buttons depending on the duration of a sample stimulus (a blue square on a computer monitor). Delays (0, 8, 16, and 32s) separated sample and comparison stimuli (two white boxes) and were tested both within and across several sessions. Intermediate durations (probe stimuli between 2 and 4s) were also presented. The addition of a delay between the sample and comparison stimuli produced a bias to judge intervals as short when the 8 and 32-s delays were tested across sessions and when the 0, 16, and 32-s delays were tested within the same session. Thus, the choose-short effect was produced in human subjects using the interval bisection procedure regardless of delay length.     

Effects of food quality on maturation rate in Arctic charr, Salvelinus alpinus (L.)

The effects of food quality on maturation rate were followed in progeny from wild Arctic charr, caught in Lake Fattjaure, northern Sweden. The fish were reared at five different food quality levels. In the first summer, the fry were given feed of three qualities: diluted with cellulose in three proportions (0, 15 and 25%). During the second winter the impact of changed food quality level was studied by transferring half the fish from the high (control) to the low food quality level and vice versa.
Maturation rate was lower in males reared at the high and improved food quality levels than in males reared at the medium, low and reduced food quality levels. The maturation rate in females was similar at all levels, though the rate tended to increase at the reduced food quality level.
Fish reared at the high and medium levels had similar growth rates, whereas fish at the low food quality level experienced slower growth. Reduced food quality did not arrest the growth offish, whereas improved food quality enhanced their growth.     

Effects of environmental variation on extinction and establishment

Theoretical models predict that increasing environmental variation increases the probability of extinction, decreases the probability of establishment, and influences the distribution of times to extinction or establishment. We conducted an experiment with 281 independent populations of Daphnia magna under controlled laboratory conditions to test these predictions. Consistent with the theory, the fraction of populations going extinct increased and the fraction of populations establishing self‐sustaining populations decreased under higher levels of environmental variation compared with controls. Time to extinction decreased under higher levels of environmental variation, but we found no effect on time to establishment. These results are consistent with theoretical predictions from models of extinction. They therefore support the use of stochastic population models to predict the fates of introductions of non‐indigenous species or native endangered species based on historic fluctuations and/or expected future conditions.     

Effects of microhabitat and metabolic rate on food intake,growth and fecundity of two competing coral reef fishes

Spinyhead blennies (Acanthemblemaria spinosa) and roughhead blennies (A. aspera) are planktivorous hole-dwelling fishes that live in dead coral skeletons. Both species are known to choose shelters high above the reef surface (although spinyheads displace roughheads downwards). To test the hypothesis that this preference is due to greater plankton availability in higher locations, fish were placed on artificial habitats located 15 cm and 100 cm above the surface of a natural reef. Both species experienced higher feeding rates, growth rates, and fecundities in high locations, and spinyhead rates generally exceeded roughhead rates at a given height. Under laboratory conditions, oxygen consumption by spinyheads was 1.6 times greater than that of roughheads and this corresponds well with the 1.8 ratio of feeding rates under controlled aquarium conditions. This information provides a partial explanation for the observed microhabitat distribution and resulting coexistence of these competing species: it is hypothesized that spinyheads have an advantage in agonistic interactions because of their higher metabolic rates, thus excluding roughheads from high sites, but that roughheads can persist at low sites because their lower metabolic rates result in lower food demands. A model is presented that predicts varying occurrences and vertical distributions of these species in locations with different zooplankton densities.     

Reinforcer devaluation by extinction depends on the food restriction protocol

A common feature of reinforcer devaluation studies is that new learning induces the devaluation. The present study used extinction to induce new learning about the conditioned reinforcer in a heterogeneous chain schedule. Rats pressed a lever in a heterogeneous chain schedule to produce a conditioned reinforcer (light) associated with the opportunity to obtain an unconditioned reinforcer (food) by pulling a chain. The density of food reinforcement correlated with the conditioned reinforcer was varied in a comparison of continuous and variable-ratio reinforcement schedules of chain pulling; this had no noticeable effect on conditioned reinforcer devaluation produced by extinction of chain pulling. In contrast, how rats were deprived appeared to matter very much. Restricting meal duration to 1h daily produced more lever pressing during baseline training and a greater reductive effect of devaluation on lever pressing than restricting body weight to 80% of a control rat's weight, which eliminated the devaluation effect. Further analysis suggested that meal-duration restriction may have produced devaluation effects because it was more effective than weight restriction in reducing rats' body weights. Our results exposed an important limitation on the devaluation of conditioned reinforcers: slight differences in food restriction, using two commonly employed food-restriction procedures, can produce completely different interpretations of reinforcer devaluation while leaving reinforcer-based learning intact.     

Effects of light on circadian pacemaker development

The effects of raising cockroaches, Leucophaea maderae, in non-24-h light cycles on the response of the circadian system to light was examined. 1. Phase response curves (PRC) were measured for 6-h light pulses for animals raised in LD 11:11 (T22), LD 12:12 (T24), and LD 13:13 (T26). The delay portion of the PRC was found to be significantly reduced in T22 animals (compared to T24 animals) while the advance portion of the PRC was reduced in T26 animals. Compared to T26 animals, phase shifts were more positive at every phase for animals raised in T22. 2. When transferred from constant darkness (DD) to constant light (LL) the freerunning period lengthened significantly less for T22 animals than T24 animals, and in some cases tau in LL was actually shorter than tau in DD in T22 animals. Animals raised in LL were inactive when exposed to LL as adults, and unlike T24 animals, were consistently reset to the beginning of the subjective night (near CT 12) when transferred to DD. 3. Roaches raised in T22 would entrain to LD 6:18, but a few animals exhibited periods of relative coordination indicating that the 24-h light cycle was near the limits of entrainment. These results indicate that the circadian system's responsiveness to light, as well as its freerunning period (Barrett and Page 1989), is dependent on the lighting conditions to which the animals are exposed during development.