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At least 721 records · Page 40Linked to original sources
PubMed1985

Effects of post-trial injection of beta-endorphin on shock-induced fighting are dependent on baseline of fighting.

The effects of repeated post-trial administration of 10 micrograms/kg beta-endorphin on the development of mutual fighting in pairs of rats submitted to various intensities of electric shock were investigated. beta-Endorphin blocked the development of fighting responses when a low footshock intensity was used, but facilitated it when a high shock intensity was delivered. A detailed analysis of the relationship between shock intensity, baseline of fighting, and effects of beta-endorphin showed that the effects of beta-endorphin were dependent on the behavioral baseline rather than on shock intensity per se.

Animals↗
PubMed2004

Classifying life-style types of phytoseiid mites: diagnostic traits.

Several traits are useful for identifying life-style types of predaceous phytoseiid mites when either 2 (diet generalist-specialist) or 4 (specialist I and II-generalist III and IV) type models [McMurtry J.A. and Croft B.A. 1997. Annu. Rev. Entomol. 42: 291-321] are considered. Traits useful for both models are developmental time and oviposition rates when feeding on several food types. Discriminating for the 2-types model are dorsal shield setae lengths, and intra- and inter-specific predation. Another trait useful for both models is feeding preferences of adult female phytoseiids on eggs versus larvae of Tetranychus urticae Koch. In this paper, we review established and other traits that need more study such as mouthpart types, other morphological features, spider mite webbing effects, distributions relative to prey-foods, plant-host relationships including domatia and sap feeding, density-dependent responses to prey and predator-prey ratios required for biological control. Uses of life-style data in biological control decision-making are discussed.

Animals↗
PubMed1995

Patterns of individual diet choice and efficiency of foraging in wedge-capped capuchin monkeys (Cebus olivaceus).

Capuchin monkeys (Cebus olivaceus) exhibit extensive intragroup variability in foraging and diet. To consider how age, sex, and individual identity contribute to this variability, the authors examined foraging and diet in 18 wedge-capped capuchin monkeys in 1 social group in the wild. Age-sex classes did not differ in the time spent ingesting food, the reliance on plant foods, the foraging actions used or substrates exploited, or in the efficiency of exploiting animal foods. They did differ, however, in the time spent finding food, time devoted to animal foods and to vigorous foraging, and the efficiency of foraging. The sexes differed more than age groups. Individual differences within age-sex class were less extensive than expected and were more evident in juveniles than adults. Within-group variability in foraging reflected catholic selection and equivalent treatment of substrates by all individuals, rather than individual specializations.

Age Factors↗
PubMed1978

Garter snake trailing behavior: effects of varying prey-extract concentration and mode of prey-extract presentation.

In a multiple-choice maze, garter snakes were trained to follow earthworm-extract trails for worm bit rewards. In Experiment 1, they were tested for their abilities fo follow extract trails that had been dried or extract trails that were removed from direct lingual access by a perforated floor. Snakes were able to follow the dry trails and unable to follow removed trails. In Experiment 2, snakes were tested for their behavioral responses to different concentrations of extract trails. Snakes trailed more accurately, moved more slowly, and exhibited much higher tongue flick rates on the intense concentration trails. The results are interpreted in terms of the assumption that effective trails are perceived by the tongue flick delivery of odorants to the vomeronasal organs.

Animals↗
PubMed2005

Asymptotic prey profitability drives star-nosed moles to the foraging speed limit.

Foraging theory provides models for predicting predator diet choices assuming natural selection has favoured predators that maximize their rate of energy intake during foraging. Prey profitability (energy gained divided by prey handling time) is an essential variable for estimating the optimal diet. Time constraints of capturing and consuming prey generally result in handling times ranging from minutes to seconds, yet profitability increases dramatically as handling time approaches zero, providing the potential for strong directional selection for increasing predator speed at high encounter rates (tiny increments in speed increase profitability markedly, allowing expanded diets of smaller prey). We provide evidence that the unusual anatomical and behavioural specializations characterizing star-nosed moles resulted from progressively stronger selection for speed, allowing the progressive addition of small prey to their diet. Here we report handling times as short as 120 ms (mean 227 ms) for moles identifying and eating prey. 'Double takes' during prey identification suggest that star-nosed moles have reached the speed limit for processing tactile information. The exceptional speed of star-nosed moles, coupled with unusual specializations for finding and eating tiny prey, provide new support for optimal foraging theory.

Animals↗
PubMed2006

Ecological networks and their fragility.

Darwin used the metaphor of a 'tangled bank' to describe the complex interactions between species. Those interactions are varied: they can be antagonistic ones involving predation, herbivory and parasitism, or mutualistic ones, such as those involving the pollination of flowers by insects. Moreover, the metaphor hints that the interactions may be complex to the point of being impossible to understand. All interactions can be visualized as ecological networks, in which species are linked together, either directly or indirectly through intermediate species. Ecological networks, although complex, have well defined patterns that both illuminate the ecological mechanisms underlying them and promise a better understanding of the relationship between complexity and ecological stability.

Animals↗
PubMed2005

Predation risk influences adaptive morphological variation in fish populations.

Predators can cause a shift in both density and frequency of a prey phenotype that may lead to phenotypic divergence through natural selection. What is less investigated is that predators have a variety of indirect effects on prey that could potentially have large evolutionary responses. We conducted a pond experiment to test whether differences in predation risk in different habitats caused shifts in behavior of prey that, in turn, would affect their morphology. We also tested whether the experimental data could explain the morphological variation of perch in the natural environment. In the experiment, predators caused the prey fish to shift to the habitat with the lower predation risk. The prey specialized on habitat-specific resources, and there was a strong correlation between diet of the prey fish and morphological variation, suggesting that resource specialization ultimately affected the morphology. The lack of differences in competition and mortality suggest that the morphological variation among prey was induced by differences in predation risk among habitats. The field study demonstrated that there are differences in growth related to morphology of perch in two different habitats. Thus, a trade-off between foraging and predator avoidance could be responsible for adaptive morphological variation of young perch.

Adaptation, Physiological↗
PubMed2004

Direct evidence for predation on trilobites in the Cambrian.

A fossil arthropod similar to Fuxianhuia and displaying an exceptionally well-preserved alimentary canal with in situ gut contents is reported from the lower Middle Cambrian (ca. 510 Myr ago) of South China. Three-dimensionally preserved, paired phosphatic nodules, arranged in series along both sides of the gut and containing spherical bacteria, probably represent serial digestive glands. The gut is filled with fragments of the eodiscoid trilobite, Pagetia. The well-developed digestive glands and the fragmentary trilobite remains suggest (i) that the arthropod was a durophagous, possibly selective predator, and (ii) that small trilobites such as eodiscoids were a major food source in Cambrian marine ecosystems. This fossil association augments the small number of previously described associations providing more or less direct evidence of predator-prey relationships in Cambrian epibenthic communities.

Animals↗
PubMed1996

Monogamy without biparental care in a dwarf antelope.

The only widely accepted explanations for the evolution of monogamy in mammals have been based on the benefits of biparental care of offspring. This is probably because, unless biparental care is important, the most competitive males would be expected to monopolize more than one female. This study investigates whether males are important for offspring survival in a monogamous dwarf antelope, Kirk's dik-dik (Madoqua kirkii), by testing three hypotheses that have been proposed to account for monogamy in mammals. In dik-diks, males could help their mates and young by: (i) defending resources; (ii) defending against infanticide by other males; and (iii) reducing predation risk. Because territorial defence was mainly sex-specific, males did not defend resources for their mates or offspring. Males also made no attempt to kill infants they had not sired, so there is no risk of infanticide. Nor was there any evidence that males reduced predation risk: females were not alerted to an approaching predator sooner when males were present, and only mothers responded to playbacks of the call of a predator which preys on juvenile but not adult dik-diks. This is the first conclusive evidence of the absence of paternal care in any monogamous mammal.

Animals↗
PubMed1996

Is spacing behaviour coupled with predation causing the microtine density cycle? A synthesis of current process-oriented and pattern-oriented studies.

Current ecological information on periodically fluctuating microtine populations are demonstrated to support a hypothesis involving both predation and intrinsic self-regulation as necessary and sufficient factors for explaining the "microtine density cycle'. The structure of the cyclic time series is largely two dimensional with strong delayed density dependence. Together with recent field studies on rodent demography, our modelling suggests that trophic interaction is a likely candidate to generate the dimensionality observed for northern microtine rodent dynamics. It is shown that the trophic interaction must be fairly strong. This suggests that specialist predation is the most likely one among the classes of trophic interactions. We also argue that some - but not too strong - self-regulation must occur to generate the structure of the available time series on northern European microtines.

Animals↗
PubMed1999

A trade-off between energy intake and exposure to parasites in oystercatchers feeding on a bivalve mollusc.

Models of animal dispersion between habitat patches that differ in resource density assume that animals maximize their fitness by maximizing the rate at which they consume resources. How valid is this assumption? Studies on wading birds have been central to the application of dispersion models to predator-prey systems. However, these birds do not always attempt to maximize their rate of energy intake, implying that maximization involves costs as well as benefits. Overwintering oystercatchers feeding on cockles in the Burry Inlet, South Wales, do not consume the larger more energetically profitable cockles even though consuming these prey would increase their rate of energy intake. This paper tests the hypothesis that maximizing energy intake involves a trade-off with exposure to helminth parasites. Cockles are important intermediate hosts for helminth parasites, for which oystercatchers are the definitive host. The helminth intensity of cockles increased significantly with cockle size. A functional response model was used to examine how size selection by the birds influenced energy intake and the ingestion rate of parasites. To maximize energy intake birds should selectively consume the larger size classes, but to minimize the ingestion rate of parasites they should consume the smallest size classes. In the wild, birds selectively consumed intermediate size classes, which could represent a compromise between these conflicting demands. The implications for animal dispersion models are discussed.

Animals↗
PubMed2000

Crickets with extravagant mating songs compensate for predation risk with extra caution.

Modern models for the evolution of conspicuous male mating displays assume that males with conspicuous displays must bear the cost of enhanced predation risk. However, if males can compensate behaviourally for their increased conspicuousness by acting more cautiously towards predators, they may be able to lower this cost. In the field cricket Gryllus integer, males call to attract females, and differ in their durations of uninterrupted trilling (calling-bout lengths). Differences among males in calling-bout lengths are heritable, and females prefer males with longer calling bouts. In this study, males with longer, more conspicuous songs behaved more cautiously than males with shorter songs on two different tests of predator avoidance. They took longer to emerge from a safe shelter within a novel, potentially dangerous environment, and they ceased calling for a longer time when their calls were interrupted by a predator cue. Thus, these males appear to compensate behaviourally for their more conspicuous mating displays. Additionally, latencies to emerge from a shelter in the novel environment were consistent over time for both individual males from the field and males that had been reared in the laboratory, indicating that the differences in latency among males may be heritable.

Animals↗
PubMed2000

Evidence for a rule governing the avoidance of superfluous escape flights.

When an imminent attack by a predator on a group of birds is signalled to non-detectors only by the departure of the detector, non-detectors may make time-wasting false-alarm flights in response to mistaken or non-predator-driven departures. The frequency of false-alarm flights might be reduced if group members assess the reason for single departures before responding. Immediate flights should only occur after multiple simultaneous departures, because these are only likely to be generated by an attack. The response delay between the detectors' departure and the next birds that respond should then be dependent on the number of detectors. On sparrowhawk attack, response delays in redshanks decreased significantly as detector number increased, controlling for raptor conspicuousness and proximity, and flock size and spacing. If response delay is modified because of risk dilution, it should increase with flock size and, consequently, the rate of alarm flights due to mistakes should decrease. However, response delay did not increase and flight frequency due to misidentification of non-raptors or non-predator-driven departures did not decrease with flock size. Significantly more feeding time was lost by birds in small flocks, suggesting that the dilution effect decreased the cost of each false-alarm flight rather than their frequency.

Animal Communication↗
PubMed2004

Is death-feigning adaptive? Heritable variation in fitness difference of death-feigning behaviour.

The adaptation of death-feigning (thanatosis), a subject that has been overlooked in evolutionary biology, was inferred in a model prey-and-predator system. We studied phenotypic variation among individuals, fitness differences, and the inheritance of death-feigning behaviour in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Two-way artificial selections for the duration of death-feigning, over 10 generations, showed a clear direct response in the trait and a correlated response in the frequency of death-feigning, thus indicating variation and inheritance of death-feigning behaviour. A comparison of the two selected strains with divergent frequencies of death-feigning showed a significant difference in the fitness for survival when a model predator, a female Adanson jumper spider, Hasarius adansoni Audouin (Araneomophae: Salticidae), was presented to the beetles. The frequency of predation was lower among beetles from strains selected for long-duration than among those for short-duration death-feigning. The results indicate the possibility of the evolution of death-feigning under natural selection.

Adaptation, Biological↗