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PubMed2005

Omnivory and the stability of food webs.

The ecological concept of omnivory, feeding at more than a single trophic level, is formulated as an intermediate stage between any two of three classical three-dimensional species interaction systems-tritrophic chain, competition, and polyphagy. It is shown that omnivory may be either stabilizing or destabilizing, depending, in part, on the conditions of the parent systems from which it derives. It is further conjectured that the tritrophic to competition gradient cannot be entirely stable, that there must be an instability at some level of intermediate omnivory.

Animals↗
PubMed2005

Die hard: a blend of freezing and fleeing as a dynamic defense--implications for the control of defensive behavior.

Freezing, fleeing or fighting back are general defensive responses in many taxa. These defenses are mutually exclusive, since a prey cannot simultaneously flee and fight, or freeze and flee. Each of these defenses by itself is rudimentary and probably cannot provide a completely effective means to elude predation. Freezing is efficient only if employed before the prey is spotted by the predator, otherwise the prey becomes a stationary, easy to catch target. In fleeing, the prey can move directly away and maximize its distance from the predator, move toward the predator to confine it to a single clashing point, or dodge sideways to evade the attack. Prey can also run in a straight path that is efficient against slow or distant predators, or in a zigzag path that is efficient when a raptor is close or fast. In all, freezing and fleeing constitute together a complex and flexible defensive response, and are probably controlled by different motor systems that are inter-connected to allow fast switching between these behaviors, as required for an effective and versatile response.

Animals↗
PubMed2005

The effects of predator odors in mammalian prey species: a review of field and laboratory studies.

Prey species show specific adaptations that allow recognition, avoidance and defense against predators. For many mammalian species this includes sensitivity towards predator-derived odors. The typical sources of such odors include predator skin and fur, urine, feces and anal gland secretions. Avoidance of predator odors has been observed in many mammalian prey species including rats, mice, voles, deer, rabbits, gophers, hedgehogs, possums and sheep. Field and laboratory studies show that predator odors have distinctive behavioral effects which include (1) inhibition of activity, (2) suppression of non-defensive behaviors such as foraging, feeding and grooming, and (3) shifts to habitats or secure locations where such odors are not present. The repellent effect of predator odors in the field may sometimes be of practical use in the protection of crops and natural resources, although not all attempts at this have been successful. The failure of some studies to obtain repellent effects with predator odors may relate to (1) mismatches between the predator odors and prey species employed, (2) strain and individual differences in sensitivity to predator odors, and (3) the use of predator odors that have low efficacy. In this regard, a small number of recent studies have suggested that skin and fur-derived predator odors may have a more profound lasting effect on prey species than those derived from urine or feces. Predator odors can have powerful effects on the endocrine system including a suppression of testosterone and increased levels of stress hormones such as corticosterone and ACTH. Inhibitory effects of predator odors on reproductive behavior have been demonstrated, and these are particularly prevalent in female rodent species. Pregnant female rodents exposed to predator odors may give birth to smaller litters while exposure to predator odors during early life can hinder normal development. Recent research is starting to uncover the neural circuitry activated by predator odors, leading to hypotheses about how such activation leads to observable effects on reproduction, foraging and feeding.

Animals↗
PubMed2004

Development of defensive behavior and conditioning to cat odor in the rat.

Laboratory rats show a range of defensive behaviors, including freezing, avoidance, and risk assessment upon exposure to cat odor, an unconditioned but highly effective threat stimulus. This study examined defensive behaviors, and the rapid conditioning to context plus cue, of these behaviors, in 18-, 26-, and 38-day-old male and female rats exposed to cat odor. Rats were placed individually in a runway with a cloth covered (control or saturated with cat fur/skin odor) block for a 10-min trial. On the following day, a similar trial involved an odorless block. On the odor exposure day, rats of all ages showed less contact with the odor block than with the control block. The 26- and 38-day-old rats, but not the 18-day-old rats, also showed locomotor suppression, more avoidance of the area where the odor block was located, and more risk assessment than no-odor controls. On a test of conditioned behavior 24 h following exposure, 26- and 38-day-old rats exhibited defensive behavior including avoidance and reduction of locomotion while 18-day-old pups did not.

Age Factors↗
PubMed2004

Long-lasting, selective, anxiogenic effects of feline predator stress in mice.

Lasting increases in anxiety-like behavior (ALB) are produced by brief exposure of rats to a cat [Adamec RE, Shallow T, Lasting effects on rodent anxiety of a single exposure to a cat, Physiol. Behav., 54 (1993) 101-109.]. Mice also respond defensively to natural predator stimuli. Moreover, chronic exposure of mice to rat odor has immediate anxiogenic effects in plus maze and lasting (7 days) and effects on acoustic startle. The present study examined the lasting (7 days) after effects on ALB of a brief unprotected exposure of male CFW mice to a cat. Lasting effects on ALB of exposure to the cat exposure room were also assessed. Effects on behavior were studied in the hole board and elevated plus-maze (EPM). An ethological analysis of behavior revealed that risk assessment in the EPM was increased the most in predator-stressed mice. Mice exposed to the cat exposure room showed increased risk assessment falling between controls and cat exposed mice. Behavior in the hole board was unaffected, as were most other behaviors in the plus maze. Factor analysis revealed independence of risk assessment from other measures of ALB, activity and exploration, consistent with findings in rats. Aspects of the stress experience were highly predictive of later response to the cat. Cat biting and pawing, mouse fleeing and mouse weight measured at the time of cat exposure together accounted for 71% of the variance of risk assessment in cat exposed mice. The significance of these findings for vulnerability to cat predator stress of mice and for the use of predator stress in mice as a model of aspects of posttraumatic stress disorder (PTSD) are discussed.

Animals↗
PubMed2003

Parasite altered micro-distribution of Gammarus pulex (Crustacea: Amphipoda).

In a river survey, Gammarus pulex amphipods both unparasitised and parasitised with the acanthocephalan Echinorhynchus truttae were distributed similarly with respect to flow regimen, tending to be more abundant in faster, shallower, riffle patches. However, there was a higher prevalence of parasitism in faster, shallower areas than in slower, deeper areas and abundance correlated with macrophyte coverage for unparasitised but not parasitised amphipods, indicating subtle differences in habitat usage. A laboratory 'patch' simulation indicated that parasitism influenced micro-distribution. There were higher proportions of unparasitised amphipods in/under stone substrates and within weed. In contrast, there were higher proportions of parasitised amphipods in the water column and at the water surface. As the experiment progressed, unparasitised but not parasitised amphipod habitat usage shifted from those micro-habitats above the substrate and in the water column to those in/under the substrates. Experiments also demonstrated that parasitised amphipods were more active and had a greater preference for illumination. Previous studies of the effects of acanthocephalan parasitism of amphipod hosts have focussed on how drift behaviour is altered, now we show that subtle differences in micro-habitat usage could translate to greatly increased vulnerability to fish predation. We discuss how aggregation of parasitised individuals within specific habitats could promote parasite transmission.

Acanthocephala↗
PubMed2003

Parasite-induced trophic facilitation exploited by a non-host predator: a manipulator's nightmare.

Parasites with complex life cycles, relying on trophic transmission to a definitive host, very often induce changes in the behaviour or appearance of their intermediate hosts. Because this usually makes the intermediate host vulnerable to predation by the definitive host, it is generally assumed that the parasite's transmission rate is increased, and that the modification of the host is, therefore, of great adaptive significance to the parasite. However, in the ecological "real world" other predators unsuitable as hosts may just as well take advantage of the facilitation process and significantly erode the benefit of host manipulation. Here we show that the intertidal New Zealand cockle (Austrovenus stutchburyi), manipulated by its echinostome trematode (Curtuteria australis) to rest on the sediment surface fully exposed to predation from the avian definitive host, is also subject to sublethal predation from a benthic feeding fish (Notolabrus celidotus, Labridae). The fish is targeting only the cockle-foot, in which the parasite preferentially encysts, reducing the infection intensity of manipulated cockles to levels comparable with those in non-manipulated, buried cockles. Based on the frequency and intensity of the foot cropping and predation rates on surfaced cockles by avian hosts, it is estimated that 2.5% of the parasite population in manipulated cockles is transmitted successfully whereas 17.1% is lost to fish. We argue that the adaptive significance of manipulation in the present system depends critically on the feeding behaviour of the definitive host. If cockles constitute the majority of prey items, there will be selection against manipulation. If manipulated cockles are taken as an easily accessible supplement to a diet composed mostly of other prey organisms, behavioural manipulation of the cockle host appears a high risk, high profit transmission strategy. Both these feeding behaviours of birds are known to occur in the field.

Animals↗
PubMed2001

Does long term potentiation in periacqueductal gray (PAG) mediate lasting changes in rodent anxiety-like behavior (ALB) produced by predator stress?--Effects of low frequency stimulation (LFS) of PAG on place preference and changes in ALB produced by predator stress.

The effects on rodent behavior of low frequency bilateral stimulation (LFS, 900 pulses at 1 Hz) of periacqueducatal gray (PAG) was investigated. The first experiment examined aversive qualities of LFS in a place preference paradigm. There was no evidence of a place preference after 1 or 7 applications of LFS. After the first LFS, rats showed longer latencies to leave the conditioned chamber, suggesting a positively reinforcing effect of LFS. Latency differences were not accounted for by freezing or immobility prior to leaving. Rats with electrodes outside the PAG did not show these effects. After repeated LFS, stimulated rats did not differ from controls in place preference or in anxiety-like behavior (ALB). Experiment 2 studied the effects of predator stress in unimplanted rats on an extended battery of measures of ALB in hole board, plus maze and light/dark box tests of rodent anxiety. Effects of electrode damage in the PAG on ALB was also examined. In addition, the effect of 7 applications of bilateral LFS of PAG on ALB following a 5 min unprotected exposure of rats to a cat (predator stress) was examined. Predator stress lastingly changed a wide variety of behaviors in the plus maze, [Rodgers, Behav. Pharmacol. 8 (1997) 477] replicating and extending previous reports. A new finding is an increase in light avoidance in the light/dark box test. Moreover, factor analysis revealed open arm avoidance, risk assessment, light avoidance and cautious exploration loaded on independent factors, replicating and extending previous findings. Bilateral, but not unilateral, damage specific to PAG was also found to be anxiolytic in plus maze measures of ALB. Bilateral implants in the PAG seemed to prevent many of the effects of predator stress on ALB measured 8 days later. Nevertheless, predator stress did decrease head dips in the open arm and LFS reversed this effect. Light avoidance also increased following predator stress and LFS reversed this increase. These findings suggest the PAG occupies an important position in the final common path of substrate changes mediating effects of predator stress on a range of behaviors in the rodent. The fact that LFS in the PAG can reverse stress induced changes in behavior supports the idea that LTP in PAG mediates stress induced increases in anxiety in rodents, as it does in the cat [Adamec, Neurosci. Biobevav. Rev. 21(6) (1997) 755; Adamec, J. Psychopharmacol. 2000 (in press); Adamec, J. Psychopharmacol. 2000 (in press); Adamec, J. Psychopharmacol. 12(2) (1998) 129; Adamec, J. Psychopharmacol. 12(13) (1998) 227].

Animals↗
PubMed2001

Delayed effects of embryonic exposure of zebrafish (Danio rerio) to methylmercury (MeHg).

Since previous short-term bioassays of methylmercury (MeHg) indicated no morphological effects in zebrafish (Danio rerio) after embryonic exposures below 20 microg/l MeHg, studies were done to determine whether embryonic exposure to MeHg at lower concentrations would induce behavioral effects. Newly fertilized embryos were exposed to 0, 5, 10 or 15 microg MeHg/l for selected exposure durations: single day, multiple day or continuous exposure from fertilization through hatching. Larvae were maintained in an essential salt solution after hatching. Spontaneous swimming performance and prey capture experiments were conducted. Continuous embryonic exposure to 15 microg/l caused delayed mortality syndrome (DMS). These larvae hatched normally and appeared normal, but beginning at Day 3 post-hatch (ph), general activity was severely reduced and by Day 5 ph, larvae were completely moribund; many had faint heartbeats, severely enlarged body cavities and upward flexures of the spinal cord. Most of these larvae were dead by Day 6 ph. Multi- and single-day embryonic exposures to 15 microg/l caused reduced swimming activity and prey capture ability, and by Day 4 ph, these larvae also began to show signs of DMS. Continuous embryonic exposure to 10 microg/l significantly reduced spontaneous swimming activity, which did not improve after 5 days in clean water. Similar results were seen in larvae exposed during the last 24 h of embryonic development. Prey capture ability was also impaired in larvae exposed continuously to 10 microg/l, even after 4 days in clean water. Single-day exposures to 10 microg/l did not affect prey capture ability. Larvae from the 5-microg/l exposures were not significantly different from controls for either parameter. This study reinforces the idea that functional impairment is a more subtle response to developmental toxicants than mortality or the production of morphological defects.

Animals↗
PubMed1985

Coyote control and taste aversion.

Studies in which conditioned taste aversion was used as a non-lethal method to suppress coyote predation are reviewed in light of the controversy that surrounds such research. It is concluded that the negative results obtained to date may have been due to theoretical and methodological problems in the studies. Uncritical acceptance of those results has slowed progress on an effective and inexpensive method of coyote management.

Animals↗
PubMed1985

Coyote control and taste aversion: a predation problem or a people problem?

Failures to suppress coyote predation on domestic livestock using the conditioned taste aversion paradigm may be due to such factors as poor livestock management procedures and overestimated coyote predation data, in addition to theoretical and methodological problems as indicated by Forthman Quick, Gustavson and Rusiniak.

Animals↗
PubMed1997

The role of nasal chemical senses in garter snake response to airborne odor cues from prey.

Garter snakes increase tongue-flick rates in the presence of airborne odorants (amyl acetate, limonene, earthworm wash vapor, fish water vapor, earthworms, goldfish) but not water vapor. Main olfactory (MO) nerve lesions result in loss of this tongue-flick rate elevation in the presence of airborne odorants. Vomeronasal (VN) nerve lesions result in a diminution of tongue-flick rate elevation. Garter snakes discriminate between the 2 arms of a maze containing airborne earthworm odor as compared with a blank control. Following MO nerve lesions, snakes fail to make this discrimination. Following VN nerve lesions or VN duct suture, snakes are initially able to make the discrimination but may eventually cease to prefer the prey-odor side of the maze and may stop eating prey rewards. These results support the idea that airborne odorants are detected by the main MO system and that such detection does not require a functional VN system.

Animals↗