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PubMed2006

Effects of group size and pine defence chemicals on Diprionid sawfly survival against ant predation.

The defence chemicals and behavioural adaptations (gregariousness and active defensive behaviour) of pine sawfly larvae may be effective against ant predation. However, previous studies have tested their defences against very few species of ants, and few experiments have explored ant predation in nature. We studied how larval group size (groups of 5 and 20 in Neodiprion sertifer and 10, 20 and 40 in Diprion pini) and variation in levels of defence chemicals in the host tree (Scots pine, Pinus sylvestris) affect the survival of sawfly larvae. Food preference experiments showed that ants do eat sawfly larvae, although they are not their most preferred food item. According to our results, ant predation significantly increases the mortality rate of sawfly larvae. Larval mortality was minor on pine tree branches where ant traffic was excluded. We also found that a high resin acid concentration in the host tree significantly decreased the mortality of D. pini larvae when ants were present. However, there was no such relationship between the chemical concentrations of the host tree and larval mortality for N. sertifer. Surprisingly, grouping did not help sawfly larvae against ant predation. Mortality risk was the same for all group sizes. The results of the study seemingly contradict previous understanding of the effectiveness of defence mechanisms of pine sawfly against ant predation, and suggest that ants (Formica exsecta in particular) are effective predators of sawfly larvae.

Analysis of Variance↗
PubMed2006

Testing for non-target effects of spinosad on twospotted spider mites and their predator Phytoseiulus persimilis under greenhouse conditions.

The compatibility of the selective insecticide spinosad (Conserve SC), at rates recommended for thrips control in greenhouses, with release of the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) to control spider mites, was investigated in a crop of ivy geranium Pelargonium peltatum, cultivar 'Amethyst 96.' Plants were inoculated with twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), 2 weeks before treatments were applied. There were three treatment variables, each at two levels: predators (released or not), spray application (water or Conserve SC at 2 ml/3.79 l), and timing of spray (1 day before or after predators were released). Twospotted spider mite populations then were sampled twice each week over a three-week period. The application or timing of spinosad had no effect on the ability of the predator to reduce the population of spider mites. Spider mite populations in the no-predator treatment continued to expand over the course of the experiment, while those in the predator-release treatment declined. We conclude that P. persimilis can be used in conjunction with spinosad on ivy geraniums without causing obvious detrimental effects to this predator or leading to a reduction in biological control.

Animals↗
PubMed2005

Chemical defense in harvestmen (arachnida, opiliones): do benzoquinone secretions deter invertebrate and vertebrate predators?

Two alkylated 1,4-benzoquinones were identified from the defensive secretion produced by the neotropical harvestman Goniosoma longipes (Gonyleptidae). They were characterized as 2,3-dimethyl-1,4-benzoquinone and 2-ethyl-3-methyl-1,4-benzoquinone. We tested the effectiveness of these benzoquinone secretions against several predator types, including invertebrates and vertebrates. Different predators were exposed to the harvestmen's gland secretion or to distilled water in laboratory bioassays. Our results indicate that secretions containing the 1,4-benzoquinones released by G. longipes can be an effective defense against predation, and that the effectiveness of the secretion is dependent on the predator type. The scent gland secretion repelled seven ant species, two species of large wandering spiders, and one frog species, but was not an effective defense against an opossum. Our study also demonstrates that the scent gland secretion of G. longipes can work as a chemical shield preventing the approach of three large predatory ants for at least 10 min. The chemical shield may protect the harvestman against successive attacks of the same ant worker and also allow the harvestman to flee before massive ant recruitment. Our data support the suggestion that chemical defenses may increase survival with some but not all potential predators. This variation in defense effectiveness may result from many interacting factors, including the attack strategy, size, learning ability, and physiology of the predators, as well as the chemical nature of the defensive compounds, type of emission, and amount of effluent released by the prey.

Adaptation, Physiological↗
PubMed2005

Impact of pesticide application on zooplankton communities with different densities of invertebrate predators: an experimental analysis using small-scale mesocosms.

We assessed the responses of zooplankton communities with different population densities of an invertebrate predator, Mesocyclops pehpeiensis, to insecticide (carbaryl, 0.5 mgL(-1)) in small-scale mesocosm tanks (20 L). Cladocerans were eliminated by carbaryl application at both high and low predator densities. The density of rotifers increased after the elimination of the cladocerans by carbaryl application at low-predator density but not at high-predator density. Carbaryl application increased the relative importance of predatory interactions in the zooplankton community. The results suggest that predator abundance can affect the response of a zooplankton community to carbaryl application through predation on surviving zooplankton.

Analysis of Variance↗
PubMed2006

Vulnerability to mild predator stress in serotonin transporter knockout mice.

Effect of predator stress on rat and mouse anxiety-like behavior may model aspects of post traumatic stress disorder (PTSD). A single cat exposure of wild type (C57, CFW) mice can produce lasting anxiety-like effects in the elevated plus maze, light/dark box tests and startle. In addition, female but not male C57 mice are made more anxious in the plus maze by exposure to predator odors alone, suggesting differential vulnerability to predator stressors of differing intensity. There is a link between genetic variation in the serotonin (5-HT) transporter (SERT) and anxiety in humans. This prompted the generation of SERT knockout mice [see Holmes A, Murphy DL, Crawley, JN. Biol Psychiatry 2003;54(10):953-9]. Present work used these mice to determine if there was a link between vulnerability to the anxiogenic effects of predator odors and abnormalities of 5-HT transmission induced by a life long reduction in 5-HT reuptake. Wild type (WT, C57 background), heterozygous (SERT +/-, HET) mice and homozygous knockout (SERT -/-, KO) were assigned to handled control groups or groups exposed for 10 min to a large testing room rich in cat odor. One week after handling or room exposure, anxiety testing took place in the dark phase of the light/dark cycle, in red light. Predator odor exposure was selectively anxiogenic in the plus maze and light/dark box tests in SERT -/- mice. Exposure to predator odor did not potentiate startle. Findings suggest a role for abnormalities in 5-HT transmission in vulnerability to some of the lasting anxiogenic effects of species relevant stressors and possibly in vulnerability to PTSD.

Animals↗
PubMed2006

Density-dependent effects of prey defenses and predator offenses.

Defenses protect prey, while offenses arm predators. Some defenses and offenses are constitutive (e.g. tortoise shells), while others are phenotypically plastic and not always expressed (e.g. neckteeth in water fleas). All of them are costly and only adaptive at certain prey densities. Here, I analyse such density-dependent effects, applying a functional response model to categorize defenses and offenses and qualitatively predict at which prey densities each category should evolve (if it is constitutive) or be expressed (if it is phenotypically plastic). The categories refer to the step of the predation cycle that a defense or offense affects: (1) search, (2) encounter, (3) detection, (4) attack, or (5) meal. For example, prey warning signals such as red coloration prevent predator attacks and are hence step 4 defenses, while sharp predator eyes enhance detection and are step 3 offenses. My theoretical analyses predict that step 1 defenses, which prevent predators from searching for their next meal (e.g. toxic substances), evolve or are expressed at intermediate prey densities. Other defenses, however, should be most beneficial at low prey densities. Regarding predators, step 1 offenses (e.g. immunity against prey toxins) are predicted to evolve or be expressed at high prey densities, other offenses at intermediate densities. I provide evidence from the literature that supports these predictions.

Animals↗
PubMed2006

Lasting anxiogenic effects of feline predator stress in mice: sex differences in vulnerability to stress and predicting severity of anxiogenic response from the stress experience.

Previous work in male Swiss Webster (CFW) mice demonstrated a long lasting effect of predator stress on risk assessment in the elevated plus maze (EPM). Most severe effects (increases in risk assessment) were seen following a brief unprotected exposure to a cat. Lesser effects were produced by a brief exposure of mice to the cat exposure room without a cat in the room (room stress). This graded response is analogous to the covariation of symptom severity and severity of the precipitating stressor in posttraumatic stress disorder (PTSD). The present study extended these findings to another strain of mice, C57/BL6, and a broader range of tests of anxiety-like behavior, including EPM, acoustic startle response and light/dark box test. Sex was introduced as a variable to investigate if females might be more susceptible to the effects of stressors than males, as has been suggested in human PTSD. Graded and lasting (7 days) effects of a 10 min exposure to a cat (predator stress) or to the cat exposure room only (room stress) were observed on lighted chamber avoidance in the light/dark box. Room stress was without effect on startle responses, but predator stress enhanced peak startle amplitudes measured in the light or in the dark. There was no evidence of light-enhancement of startle in C57 mice. Female mice were more susceptible to the effects of predator and room stress, depending on the measure. Females only responded to cat exposure with a lasting increase in average startle amplitude. This was due to an increased and more prolonged multipeak response to startle after the first and maximal peak startle response. In addition, in females, room and predator stress were equally anxiogenic in measures of open arm avoidance in the EPM. In contrast, room stress was without effect on open arm avoidance in males, but cat exposure was as anxiogenic in males as it was in females. These findings suggest EPM anxiety in females is affected more by the milder stress of room exposure. Severity of effects of predator stress on anxiety-like behaviors in EPM and startle were well predicted (60% of the variance) by measures of cat behavior and probability of mouse defensive response to particular cat behaviors during the cat exposure. Finally, factor analysis indicated that different tests of anxiety-like behavior may be measuring different and independent aspects of mouse affect. Moreover, stressors had no lasting effects on sugar solution consumption. Implications of these findings for modeling PTSD and using transgenic strains of mice to study lasting effects of stress on affect are discussed.

Analysis of Variance↗
PubMed2004

A predator-prey model with infected prey.

A predator-prey model with logistic growth in the prey is modified to include an SIS parasitic infection in the prey with infected prey being more vulnerable to predation. Thresholds are identified which determine when the predator population survives and when the disease remains endemic. For some parameter values the greater vulnerability of the infected prey allows the predator population to persist, when it would otherwise become extinct. Also the predation on the more vulnerable prey can cause the disease to die out, when it would remain endemic without the predators.

Animals↗
PubMed2006

Effects of predation pressure on species packing on a resource gradient: insights from nonlinear dynamics.

The classical case of three competitors arranged on a resource gradient such that the central competitor will be excluded due to competition from the other two is studied from the point of view of the effects of added predators. The basic formulation is motivated by a desire to understand the effects of asymmetries in multidimensional Lotka-Volterra systems. We first study the effects of perfectly specialist predators and find a rich collection of possible behaviors of the system including (1) extinction of all predators and subsequent extinction of the subordinate competitor, (2) dominant competitors and their predators coexist but the subdominant competitor goes extinct, (3) all species except the predator of the subordinate competitor coexist in coordinated phase-reversed chaos, (4) exclusion of one or more species occurs through an expanding heteroclinic cycle, and (5) all species coexist in an uncoordinated chaos. We then study the effects of five qualitatively distinct forms of polyphagy. In one case, corresponding to the well-known vulnerability to predation versus competitive ability trade-off, it is possible to have the subordinate competitor be the only survivor in the system. The other three cases of polyphagy lead to distortions in the basic pattern seen in the previously analyzed specialist case. Studying this case of ecologically motivated asymmetries in the basic Lotka-Volterra formulation is a step in the direction of fully understanding interacting populations.

Animals↗
PubMed2005

Modelling nitrification, heterotrophic growth and predation in activated sludge.

A mathematical model describing the interaction between nitrifiers, heterotrophs and predators in wastewater treatment has been developed. The inclusion of a predation mechanism is a new addition to the existing activated sludge models. The developed model considered multi-substrate consumption and multi-species growth, maintenance and decay in a culture where nitrifiers, heterotrophs and predators (protozoa and metazoa) are coexisting. Two laboratory-scale sequenced batch reactors (SBRs) operated at different sludge retention time (SRT) of 30 and 100 days for a period of 4 years were used to calibrate and validate the model. Moreover, to assess the predator activity, a simple procedure was developed, based on measuring the respiration rate with and without the presence of the predators. The model successfully described the performance of two SBRs systems. The fraction of active biomass (ammonia oxidisers, nitrite oxidisers and heterotrophs) predicted by the proposed model was only 33% and 14% at SRT of 30 and 100 days, respectively. The high fraction of inert biomass predicted by the model was in accordance with the microscopic investigations of biomass viability in both reactors. The presented model was used to investigate the effect of increasing sludge age and the role of predators on the biomass composition of the tested SBR system.

Animals↗
PubMed2000

Mortality, behavior and the effects of predators on the intertidal distribution of littorinid gastropods.

Predators can affect the vertical distribution of mobile intertidal invertebrates in two ways: they can (1) cause greater mortality of prey at certain intertidal levels, and (2) induce prey to seek safer intertidal areas. In this study, we investigate whether low-intertidal and subtidal predators affect the intertidal distribution of two congeneric species of small herbivorous gastropods of northeastern Pacific shores, Littorina sitkana Philippi 1846, and L. scutulata Gould 1849. In particular, we tested the hypothesis that predators affect the distribution of these snails by inducing them to seek higher and safer intertidal areas. On a wave-sheltered shore in Barkley Sound, British Columbia, L. sitkana and L. scutulata were both killed by predatory crabs (e.g., Cancer productus) more frequently when tethered near the lower limit of their intertidal distribution ( approximately 1 m) than when tethered where they were most common ( approximately 2.5 m), suggesting that high mortality rates are partly responsible for the lower-limit of these snails' intertidal distribution. However, two field mark-recapture experiments indicated that the snails' behavioral response to predation risk also influences their distribution. In the first experiment, snails from the 2.5-m level (low risk) transplanted to the 1.0-m level (high risk) displayed a strong and consistent tendency to move shoreward, especially L. sitkana, some traveling 10-15 m in 2-3 days to regain their original level. These shoreward movements were especially precise in the northern part of the study area, where predation rates on tethered snails were greatest. Furthermore, larger more vulnerable snails were more strongly oriented shoreward than smaller individuals, indicating that antipredator behavior might also contribute to intertidal size gradients in these species. In the second mark-recapture experiment, we manipulated predation risk using small cages and found that snails exposed to the odors of C. productus crabs foraging on conspecific and heterospecific snails displayed more precise (L. sitkana and L. scutulata) and longer (L. sitkana) shoreward movements than snails held in control conditions. These results provide the first experimental evidence that antipredator behavior may contribute to the intertidal distribution patterns of littorinids.

Journal Article↗
PubMed2000

Dynamics of prey moving through a predator field: a model of migrating juvenile salmon.

The migration of a patch of prey through a field of relatively stationary predators is a situation that occurs frequently in nature. Making quantitative predictions concerning such phenomena may be difficult, however, because factors such as the number of the prey in the patch, the spatial length and velocity of the patch, and the feeding rate and satiation of the predators all interact in a complex way. However, such problems are of great practical importance in many management situations; e.g., calculating the mortality of juvenile salmon (smolts) swimming down a river or reservoir containing many predators. Salmon smolts often move downstream in patches short compared with the length of the reservoir. To take into account the spatial dependence of the interaction, we used a spatially-explicit, individual-based modeling approach. We found that the mortality of prey depends strongly on the number of prey in the patch, the downstream velocity of prey in the patch, and the dispersion or spread of the patch in size through time. Some counterintuitive phenomena are predicted, such as predators downstream capturing more prey per predator than those upstream, even though the number of prey may be greatly depleted by the time the prey patch reaches the downstream predators. Individual-based models may be necessary for complex spatial situations, such as salmonid migration, where processes such as schooling occur at fine scales and affect system predictions. We compare some results to predictions from other salmonid models.

Animals↗
PubMedDate not supplied

Unilateral block of NMDA receptors in the amygdala prevents predator stress-induced lasting increases in anxiety-like behavior and unconditioned startle--effective hemisphere depends on the behavior.

Lasting increases in anxiety-like behavior (ALB) in the elevated plus-maze are produced by a single 5-min exposure of a rat to a cat. Rats become more anxious in the plus-maze for up to 3 weeks after the exposure. The first study in this series demonstrated that blockade of NMDA receptors in rats with MK-801, AP7, or CPP, given systemically 30 min prior to exposure to a cat prevents the increase in ALB assessed 1 week later in the elevated plus-maze. To localize the site of action of systemic MK-801, MK-801 was injected in the amygdala 30 min prior to predator stress. Injections were given either unilaterally in either hemisphere, or bilaterally in both hemispheres. The target of the injection was the basolateral amygdala. The effects of injection depended on both the type of behavior and the hemisphere of injection. Injections of MK-801 in a variety of sites in the basolateral amygdala had no effect on the suppression of open-arm exploration produced by predator stress. Other amygdala nuclei or other limbic sites likely mediate the effects of systemically administered MK-801 on this behavior. In contrast, NMDA receptors in the left lateral amygdala mediate lasting suppression of risk assessment. MK-801, in a variety of sites in the left but not right lateral amygdala, blocked the effects of predator stress on risk assessment. This is clear evidence of separability of neural mechanisms controlling open-arm exploration and risk assessment. Different NMDA-dependent amygdala circuitry mediated effects of predator stress on unconditioned acoustic startle 1 week after cat exposure. The data indicate that integrity of the left lateral amygdala is necessary for potentiation of startle amplitude by predator stress, though NMDA receptors are not involved in this function. Nevertheless, NMDA receptors in the right, but not the left lateral amygdala, mediate initiation of changes in startle. The data also suggest that the right amygdala action is "downstream" from the left amygdala contribution. These findings are consistent with the view that NMDA receptors are involved in initiation, but not maintenance, of neural changes mediating lasting increases in anxiety following severe stress. Finally, the findings of the importance of the right amygdala in stress-induced enhancement of the startle response provides neurobiological face validity to predator stress as a model of aspects of posttraumatic stress disorder.

Amygdala↗
PubMed1999

Facultative control of avian unihemispheric sleep under the risk of predation.

Birds and aquatic mammals are the only taxonomic groups known to exhibit unihemispheric slow-wave sleep (USWS). In aquatic mammals, USWS permits sleep and breathing to occur concurrently in water. However, the function of avian USWS has been unclear. Our study is based on the premise that avian USWS serves a predator detection function, since the eye contralateral to the awake hemisphere remains open during USWS. If USWS functions as a form of predator detection, then birds should be able to control both the proportion of slow-wave sleep composed of USWS and the orientation of the open eye in response to changes in predation risk. To test these predictions we recorded eye state and the EEG of mallard ducks (Anas platyrhynchos) sleeping in groups of four birds arranged in a row. Birds at the ends of the row were more exposed than those in the central positions, who were flanked on both sides by other birds, and thus should perceive a greater risk of predation. Consistent with a predator detection function, when compared to birds in the group's center, birds at the exposed ends of the row showed a 150% increase in USWS and a preference for directing the open eye away from the group, the direction from which a predator is most likely to approach. Furthermore, during USWS mallards responded rapidly to threatening visual stimuli presented to the open eye. This ability to facultatively control sleep and wakefulness simultaneously in different regions of the brain probably involves the neuroanatomical interhemispheric separation responsible for independent hemispheric functioning during wakefulness in birds.

Animals↗
PubMed2000

The nature of predation: prey dependent, ratio dependent or neither?

To describe a predator-prey relationship, it is necessary to specify the rate of prey consumption by an average predator. This functional response largely determines dynamic stability, responses to environmental influences and the nature of indirect effects in the food web containing the predator-prey pair. Nevertheless, measurements of functional responses in nature are quite rare. Recently, much work has been devoted to comparing two idealized forms of the functional response: prey dependent and ratio dependent. Although we agree that predator abundance often affects the consumption rate of individual predators, this phenomenon requires more attention. Disagreement remains over which of the two idealized responses serves as a better starting point in building models when data on predator dependence are absent.

Journal Article↗
PubMed2003

The role of differential reinforcement in predator avoidance learning.

Little is known about how predator recognition develops under natural conditions. Predispositions to respond to some stimuli preferentially are likely to interact with the effects of experience. Convergent evidence from several studies suggests that predator-nai;ve tammar wallabies (Macropus eugenii) have some ability to respond to vertebrate predators differently from non-predators and that antipredator responses can be selectively enhanced by experience. Here, we examined the effects of differential reinforcement on responses to a model fox (Vulpes vulpes), cat (Felis catus) and conspecific wallaby. During training, tammars experienced paired presentations of a model fox and a simulated capture, as well as presentations of a wallaby and a cat alone. Training enhanced responses to the fox, relative to the conspecific wallaby, but acquired responses to the two predators did not differ, despite repeated, non-reinforced presentations of the cat. Results suggest that experience interacts with the wallabies' ability to perceive predators as a natural category.

Journal Article↗
PubMed2005

The role of eyespots as anti-predator mechanisms, principally demonstrated in the Lepidoptera.

Eyespots are found in a variety of animals, in particular lepidopterans. The role of eyespots as antipredator mechanisms has been discussed since the 19th Century, with two main hypotheses invoked to explain their occurrence. The first is that large, centrally located eyespots intimidate predators by resembling the eyes of the predators' own enemies; the second, though not necessarily conflicting, hypothesis is that small, peripherally located eyespots function as markers to deflect the attacks of predators to non-vital regions of the body. A third possibility is also proposed; that eyespots intimidate predators merely because they are novel or rarely encountered salient features. These hypotheses are reviewed, with special reference given to avian predators, since these are likely to be the principal visually hunting predators of the lepidopterans considered. Also highlighted is the necessity to consider the potential influence of sexual selection on lepidopteran wing patterns, and the genetics and development of eyespot formation.

Animals↗
PubMed2001

Laboratory and field evaluation of predator odors as repellents for kiore (Rattus exulans) and ship rats (R. rattus).

Predator odors may serve to stop rats from entering conservation areas or to decrease predation, food consumption, and other damage by rats in areas tainted with predator odor. We compared the efficacy of real predator odors and synthetic odors (derived from the urine and feces of carnivores) as rat repellents with real herbivore odors as controls in a Y maze. We tested six predator odors: cat (Felis catus) urine and feces, mongoose (Herpestes auropunctatus) feces, n-propylthietane, S-methyl, methyl butanol, and isopentyl-methyl sulphide. The herbivore odors we used were: red deer (Cervus elaphus) urine, guinea pig (Cavia porcellus) feces, and white rabbit (Oryctolagus cuniculus) urine. Ship rats (Rattus rattus) and kiore or Polynesian rats (R. exulans) showed no aversion to any of the six predator odors when compared with herbivore odors. Ship rats, however, may have avoided synthesized odors more than real ones. We applied two odors (S-methyl, methyl butanol and n-propylthietane) to purpose-built feeders in native forest but recorded no change in either visitation rate or duration of visits for rodents [rats and mice (Mus musculus)] or possums (Trichosurus vulpecula). The consumption of maize at feeders was correlated with the number and duration of possum visits, but only weakly correlated with the number of visits by rodents. Consumption of maize was unaffected by the odor associated with the feeder. It is unlikely that the odors we tested will be useful in deterring rodents or possums from areas where they have been removed for economic, public health or conservation reasons.

Animals↗