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PubMedDate not supplied

[Theoretical model of the predator-prey interaction kinetics between "Bdellovibrio bacteriovorus" and "escherichia coli" (author's transl)].

A theoretical model is suggested in order to explain the main features of the interaction kinetics between the micropredator Bdellovibrio bacteriovorus and its prey Escherichia coli. Three parametes are used in this model: the incubation time T, the fixation rate constant k, and the predator multiplication factor a. Their values can be determined from the experimental variations of the total predator concentration p, and the total density of preys (c + c'). An experimental study of the predation kinetics was performed at various temperatures (25-40 degrees C) and in media with different Ca++ and Mg++ concentrations. From the values of parameters obtained, theoretical prey and predator density curves were computer-simulated; they agree satisfactorily with the experimental curves. The parameters values are quite reasonable and in good agreement with previous findings.

Bdellovibrio↗
PubMed1978

A semi-Markovian model for predator-prey interactions.

In the study of population dynamics, the predator-prey system is recognized as a vitally important aspect in natural population control. On aspect of predator-prey interactions is studied in this paper. The attack cycle of a predator is assumed to consist of four different activities, namely, search, pursuit, handle and eat, and digestion. A semi-Markovian model is proposed to obtain the number of prey devoured by a predator during the activity of a day. The advantages of a new semi-Markovian model to the queueing model developed by Curry and DeMichele (1977) is demonstrated, as the results from the semi-Markovian model are closer to Holling's (1966) experimental data than their results, which were based entirely on Poisson assumptions.

Animals↗
PubMed1996

Toxicity of insecticides to Toxorhynchites splendens and three vector mosquitos and their sublethal effect on biocontrol potential of the predator.

Toxicity of six larvicides ie fenthion, temephos, malathion, deltamethrin, alphamethrin (Fendona), OMS 3031 and five adulticides ie malathion, fenitrothion, propoxur, deltamethrin, permethrin to Aedes aegypti, Culex quiquefasciatus, Anopheles stephensi and the predator, Toxorhynchites splendens was studied for evaluating safety margin. Concentrations of alphamethrin that killed 50% larvae of T. splendens were 53 and 12 times more than that which killed Cx. quinquefasciatus and Ae. aegypti. In case of deltamethrin, concentrations required to kill 50% larvae of T. splendens were 14 and 5 times more than that required against other two species. Other larvicides tested were equally toxic to both T. splendens and vector mosquitos. There was no significant difference in the toxicity of larvicides to T. splendens and An. stephensi. Deltamethrin was 25-132 times less toxic to adults of T. splendens in comparison to vector mosquitos. For other adulticides the range was 1-10. Immature developmental time of T. splendens was not affected by any of the insecticides tested. However, predation rate was lowered when larvae of Ae. aegypti previously exposed to fenthion and temephos were offered. Whereas, alphamethrin and OMS 3031 did not affect the feeding rate of the predator. There was a significant reduction in the pupal weight and pupation as a result of the predator feeding on the insecticide treated prey. There was a significant negative relationship between rate of pupation and dosage. The present study indicates that synthetic pyrethroids owing to their higher safety margin can be used in an integrated vector management program.

Aedes↗
PubMed2025

Adaptation in a keystone grazer under novel predation pressure.

Understanding how species adapt to environmental change is necessary to protect biodiversity and ecosystem services. Growing evidence suggests species can adapt rapidly to novel selection pressures like predation from invasive species, but the repeatability and predictability of selection remain poorly understood in wild populations. We tested how a keystone aquatic herbivore, Daphnia pulicaria, evolved in response to predation pressure by the introduced zooplanktivore Bythotrephes longimanus. Using high-resolution 210Pb-dated sediment cores from 12 lakes in Ontario (Canada), which primarily differed in invasion status by Bythotrephes, we compared Daphnia population genetic structure over time using whole-genome sequencing of individual resting embryos. We found strong genetic differentiation between populations approximately 70 years before versus 30 years after reported Bythotrephes invasion, with no difference over this period in uninvaded lakes. Compared with uninvaded lakes, we identified, on average, 64 times more loci were putatively under selection in the invaded lakes. Differentiated loci were mainly associated with known reproductive and stress responses, and mean body size consistently increased by 14.1% over time in invaded lakes. These results suggest Daphnia populations were repeatedly acquiring heritable genetic adaptations to escape gape-limited predation. More generally, our results suggest some aspects of environmental change predictably shape genome evolution.

Animals↗
PubMed2000

Psychopathy, criminal responsibility, and civil commitment as a sexual predator.

Recent judicial decisions regarding commitment under sexual predator statutes and commentary addressing the legal significance of psychopathy provide an interesting opportunity to reflect upon the exculpatory significance of psychopathy and the appropriate relationship between criminal conviction and police power civil commitment. This paper examines the legal significance of psychopathy for the purposes of criminal responsibility and of civil commitment under sexual predator statutes. By examining the significance of psychopathy for each of these legal institutions, it clarifies our understanding of the legal significance of psychopathy and of the relationship between these institutions. This process illuminates the defensible functions and boundaries of each institution and clarifies the nature of the impairment that should qualify an individual for confinement by each. This analysis interprets criminal conviction and police power commitment, including sexual predator commitment, as integrated institutions of social control intended to provide a coherent approach to psychopaths as well as to others who require state intervention under the police power.

Adult↗
PubMed1999

Aphids, predators and parasitoids.

A number of studies have demonstrated the role of herbivore-induced release of plant volatiles in mediating foraging behaviour of aphid parasitoids, particularly with the parasitoid Aphidius ervi, its aphid host Acyrthosiphon pisum and the aphid food plant Vicia faba. These studies have shown that feeding by the aphid alters the composition of volatiles released by the plant and that these compounds act as synomones for the foraging parasitoid. Of particular interest is the species-specificity of the herbivore-induced synomones associated with different aphids feeding on V. faba. Aphids employ various pheromones that mediate behaviour, particularly mating and alarm responses. These pheromones play important roles in reproduction and defence against predation and parasitism. Many species of aphids reproduce sexually on their primary hosts during the autumn and the sexual females produce a pheromone that attracts males. The sex pheromones for a number of aphid species have been identified and laboratory and field studies have shown that synthetic material can act as a kairomone in attracting predators and parasitoids. The aphid alarm pheromone is released from the cornicles of aphids when they are attacked by predators or parasitoids. The activity of the main alarm pheromone component, (E)-beta-farnesene, is inhibited by the related sesquiterpene hydrocarbon beta-caryophyllene, which is reported to attract the lacewing Chrysoperla carnea. In addition, electrophysiological studies have shown that the seven-spot ladybird, Coccinella septempunctata, possesses specific olfactory receptors for (E)-beta-farnesene and beta-caryophyllene. Laboratory studies show these compounds to have behavioural activity with C. septempunctata, suggesting that they may be involved in prey location.

Animals↗
PubMed1982

Ultrasounds in neonatal rats: novel, predator and conspecific odor cues.

Neonatal rat ultrasound repetition rates were monitored in response to 6 odor cues, including 1 novel, 2 predator, and 3 conspecific olfactory stimuli. Contrary to predictions of previous studies, predator odor did not elicit consistently low call rates. A significant difference was detected between litters tested with the same odor cue for the foreign and predator odor treatments. Odor was the only significant effect to explain differences in neonatal ultrasonic responses to conspecific odor treatments. Call rates recorded for the novel lactating female odor were significantly greater than those for the home bedding and adult male odors. Odors associated with the home cage or with an adult male elicited low call rates.

Animals↗
PubMed2003

An index for selective toxicity of miticides to phytophagous mites and their predators based on orchard trials.

Data from nine trials conducted from 1990 to 1998 in apple orchards in Nova Scotia and Quebec, Canada, were used to estimate the predator-prey selectivity of miticides and their potential compatibility with biological control of mites. The European red mite Panonychus ulmi (Koch) was the dominant and more harmful phytophagous species, followed by the apple rust mite, Aculus schlechtendali (Nalepa). Two predacious mites, the phytoseiid, Typhlodromus pyri Sheuten, and the stigmaeid, Zetzellia mali (Ewing), were often found in the orchards. We used one minus the ratio of mite-days in treated plots to those in the control plots as an index of population suppression and toxicity of the miticides. Miticides were then categorized into classes similar to those employed by the International Organization for Biological Control to rate pesticide toxicity to natural enemies of insect and mite pests. Selectivity of miticides was mostly based on toxicity to P ulmi, the major pest, versus toxicity to T pyri, the major predator, with some consideration of the two lesser species, A schlechtendali and Z mali. In most cases, our findings were in accord with other studies. Abamectin and clofentezine had favourable selectivity (more toxic to the two phytophagous mites than to T pyri). The higher recommended rate of pyridaben (450 g ha(-1)) and two rates of spirodiclofen (180 and 240 g ha(-1)) were neutral (equally toxic to pests and predators). The lower rate of pyridaben (216 g ha(-1)), dicofol, formetanate hydrochloride and propargite were unfavourably selective (more toxic to T pyri). A higher than recommended rate of pyridaben (2160 g ha(-1)) applied before bloom was disruptive--P ulmi-days after treatment were actually greater than with the untreated control. P ulmi resistance to dicofol and propargite were probable complicating factors in some of the orchard trials.

Animals↗
PubMed1998

Red squirrels, Tamiasciurus hudsonicus, produce predator-class specific alarm calls

Red squirrels, can produce alarm calls when they detect a potential predator. Observations of natural interactions between red squirrels and large birds, and predator-presentation experiments in the field, showed that red squirrels produce acoustically different alarm calls in response to aerial danger (live birds and a model hawk flown towards them) versus danger approaching from the ground (dogs and humans). The alarm call produced in response to aerial danger is acoustically convergent on the 'seet' alarm call produced by many species of passerine birds in response to raptors. The squirrels' 'seet' alarm is a short, low-amplitude, high-frequency call. These characteristics make the call difficult to localize, and is in a frequency range that is poorly perceived by raptors. Red squirrels produce much louder, wide-bandwidth bark calls in response to terrestrial danger. This is the first demonstration of predator-class specific alarm calls of red squirrels. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Soldiers effectively defend aphid colonies against predators in the field

Morphologically specialized soldiers occur in more than 50 aphid species in the families Pemphigidae and Hormaphididae. To study the effectiveness of soldiers of the gall-forming aphid, Pemphigus spyrothecae Pass., in protecting their galls against natural levels of predation, we manipulated the proportions of soldiers and non-soldiers in sets of galls still attached to poplar trees in the field. Galls with 50 soldiers and 50 non-soldiers were approximately 10 times less likely to be attacked by predators than galls that contained 100 non-soldier aphids. There were significantly fewer live aphids, and significantly more dead aphids, in galls without soldiers than in galls protected either by soldiers or by being within a bag. There were no significant differences in the survival of aphids in galls protected by soldiers compared with those protected by bagging. The soldiers did not protect the galls against invasion by the cohabiting aphid Chaitophorus leucomelas Koch. These observations provide the first demonstration that soldiers are effective in defence against natural levels of predation under field conditions. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

A reassessment of the effect of body mass upon flight speed and predation risk in birds.

A number of theoretical studies have predicted that avian predation risk is mass dependent. Models of bird flight predict that increased mass will reduce flight velocity, making birds more vulnerable to predation. Empirical studies supporting this have demonstrated a significant relationship between mass and routine flight velocity (when birds are not alarmed). Studies investigating the effects of mass upon flight velocity when birds are alarmed, however, tend to show that the mass/velocity relationship is less marked. We found a real difference in the relationship between mass and flight velocity in zebra finches, Taeniopyga guttata, when comparing flights of alarmed and unalarmed birds. Despite the strong mass/routine velocity relationship already shown for zebra finches, mass tended to be a poor predictor of the flight velocity of alarmed birds within the natural weight range of the species. This difference appeared to be partly due to alarmed birds increasing their velocity more when heavy than when light, in comparison to their respective predicted routine flight velocities for their weights. As a result, mass/velocity regression slopes tended to be more shallow for alarmed birds. Consequently, increases in body mass within the natural weight range of a bird, may have less effect on the flight velocities of alarmed birds than they do on routine flight velocities. We therefore recommend caution in the use of weight as a predictor of predation risk in birds without examining its effects upon the flight velocity of alarmed birds. We suggest some explanations for the differences in the mass/velocity relationship between the flights of alarmed and unalarmed birds. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Robot predators in virtual ecologies: the importance of memory in mimicry studies.

An important means of investigating gains and losses to prey caused by mimicry is through mathematical or computer constructs which represent and explore limited aspects of mimicry situations. Such studies use virtual predators which are usually simple automata, 'robots' that, through simple rules, vary virtual attack rates on virtual insect prey. In this paper I consider the effect of variations in predator memory and learning on mimicry dynamics. When there is mimicry between unequally noxious prey, the way that memory is modelled is shown to be crucial. If forgetting rates are fixed, an increase in the density of the least defended prey produces monotonic gains or losses in protection. However, if forgetting rate is inversely related in some way to degree of noxiousness of the prey then attack rates initially rise with the density of the least defended prey, reach a cusp and then fall. I show that the generation of this highly unconventional up-down result appears to be independent of variations in learning rate. This work shows how sensitive the predictions of virtual predators may be to relatively small changes in behavioural rules. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

The response of water voles, Arvicola terrestris, to the odours of predators.

We investigated the response of water voles to the odours of predators in outdoor enclosures. Water voles were given access to two food cages, one containing the odour of a predator and the other containing no odour, and were videotaped for 22 h. Sheep odour was also used as a control for novel odour. The predators were American mink, Mustela vison, and brown rat, Rattus norvegicus. There was no difference in the voles' response to sheep odour and no odour. The voles entered the treatment cages containing the mink's odour significantly fewer times than they entered the control cages, indicating avoidance of the former. They also gathered less food from, and stayed a shorter time inside, the treatment cages. The voles avoided the mink's odour more than the rat's odour. The fact that the experimental animals had not had previous contact with American mink suggests that the response is innate. These results also suggest that water voles perceived mink as a greater risk than rats, although they avoided odours of both these species. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Cardiac and behavioural responses of mussels to risk of predation by dogwhelks.

We used noninvasive, infrared phototransducers to record continuously the heartbeat of common mussels, Mytilus edulis, experiencing successive phases of interaction with the predatory gastropod Nucella lapillus, from initial threat to attack and consumption. Coupling physiological monitoring with behavioural analysis allowed us to investigate in detail the responses of mussels to predation threat. Compared to values of normal feeding activity, heart rate increased significantly when mussels were in the presence of effluent from dogwhelks. When attacked by dogwhelks, mussels increased their heart rate further, together with the rate of valve gaping. Considering the heart rate as a reliable estimator of respiratory function, these cardiac responses might be a mechanism to compensate for increased energy demand in order to cope with predation hazard. If so, the theoretical importance of trading off energy balance against risk of predation is supported by our results. Cardiac and behavioural responses varied throughout the attack according to the penetration method adopted by dogwhelks. When mussels were attacked through a drilled hole, heart rate tended to increase and periods of cardiac pausing appeared close to the point of death. In contrast, mussels attacked by penetration between the valves showed decreasing heart rate throughout the attack, together with relatively earlier cessation of valve gaping and appearance of cardiac pausing. These differences clearly support the hypothesis that dogwhelks penetrating between the valves are able to induce muscular paralysis of prey by injecting toxins. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Warning signals, receiver psychology and predator memory.

This review identifies four receiver psychology perspectives that are likely to be important in the design and evolution of warning signals. Three of these perspectives (phobia, learning and prey recognition) have been studied in detail, and I include a brief review of recent work. The fourth, a memory perspective, has received little attention and is developed here. A memory perspective asks, 'how might warning signals function to reduce forgetting of avoidances between encounters?'. To answer this question I review data from psychology literature that describe important features of animal long-term memory. These data suggest that components of warning signals may function to reduce forgetting (and therefore increase memorability) by (1) preventing forgetting of learnt prey discriminations; (2) jogging the memories of forgetful predators; and (3) biasing forgetting in favour of prey avoidance when the warning signal of a defended aposematic species is copied by an edible Batesian mimic. A combination of a learning and a memory perspective suggests that the features of aposematic prey that accelerate avoidance learning may also be the features that decelerate forgetting processes. If correct, this would have important implications for the comprehension of signal design. Finally, I suggest that the cryptic appearance of an edible prey may decelerate predator learning and accelerate predator forgetting, to the benefit of the prey. In terms of learning and memory, crypsis may be an antisignal. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2001

How predation can slow, stop or reverse a prey invasion.

Observations on Mount St Helens indicate that the spread of recolonizing lupin plants has been slowed due to the presence of insect herbivores and it is possible that the spread of lupins could be reversed in the future by intense insect herbivory [Fagan, W. F. and J. Bishop (2000). Trophic interactions during primary sucession: herbivores slow a plant reinvasion at Mount St. Helens. Amer. Nat. 155, 238-251]. In this paper we investigate mechanisms by which herbivory can contain the spatial spread of recolonizing plants. Our approach is to analyse a series of predator-prey reaction-diffusion models and spatially coupled ordinary differential equation models to derive conditions under which predation pressure can slow, stall or reverse a spatial invasion of prey. We focus on models where prey disperse more slowly than predators. We comment on the types of functional response which give such solutions, and the circumstances under which the models are appropriate.

Animals↗
PubMed1997

Predator-prey relationships in a two-species toxicity test system.

In a two-species toxicity test system survival and reproduction of both the predator Hypoaspis aculeifer (Gamasida) and the prey Folsomia fimetaria (Collembola) were studied after 21 days of residual exposure to a soil contamination of the insecticide dimethoate. Additional experiments were run to analyze which species-species and compound-species relationships determine the outcome of this two-species experiment. Number of adult F. fimetaria were reduced by both predation and dimethoate exposure, whereas mites preyed less efficiently on adults than on juveniles. At 0.357 mg dimethoate/kg soil, numbers of juvenile F. fimetaria were mainly reduced by predation on adults and juveniles. At 0.7 mg/kg, an additional dimethoate effect was found, which was attributed to an effect on the reproduction of F. fimetaria, mainly due to lethality of adults. It was reasoned that lethal effects on juvenile springtails are less important. Adult H. aculeifer was not affected by dimethoate exposure, whereas numbers of juvenile H. aculeifer demonstrated a decline only at the highest concentration of 0.7 mg/kg. It is hypothesized that this latter effect is possibly due to food depletion caused by a decreased availability of prey, rather than to the lethal effects of dimethoate on juvenile mites. Such a secondary effect of a pesticide application could not have been derived from a single-species toxicity experiment and demonstrates the additional value of a two-species toxicity test system.

Animals↗
PubMed2001

Brief exposure to female odors "emboldens" male mice by reducing predator-induced behavioral and hormonal responses.

In rodents, where chemical signals play a particularly important role in determining intersexual interactions, various studies have shown that male behavior and physiology is sensitive to female odor cues. Here we examined the effects of brief (1 min) and more prolonged (60 min) preexposure to the odors of a novel estrous female on the behavioral and hormonal responses of sexually experienced and inexperienced male mice, Mus musculus, to subsequent predator (cat and weasel) odor exposure and potential predator risk. Brief, but not prolonged, preexposure to the odors of an estrous female decreased the aversion and avoidance responses of male mice to cat odor in a Y-maze preference test, with the extent of responses being affected by a males prior sexual experience. Similarly, brief, but not prolonged, preexposure to female odors markedly attenuated the analgesic responses elicited in male mice by weasel odor. Brief exposure to a novel estrous female by itself had no significant immediate effects on either corticosterone or testosterone levels in the males. However, brief, but not prolonged, preexposure to the odors of an estrous female attenuated the marked increase in corticosterone and decrease in testosterone that were induced in males by exposure to weasel odor. The decreases in aversive responses to, and effects of, predator odor exposure that are induced by brief exposure to a novel estrous female may reflect a greater risk taking and boldness in males that could directly facilitate access to an immediately, and possibly transiently, available novel sexually receptive female.

Animals↗