Predator avoidance defense

Kavaliers et al. (1992) demonstrated that predator odors can elicit analgesia in mice. Temperature sensitivity was determined 15 min prior to, immediately after, and 15 min after exposure to predator odors for either 30 s or 15 min. Sensitivity was measured as the latency of a foot-licking response to a thermal stimulus (50° hot plate). Animals were significantly less sensitive (i.e., greater delay in response) when tested after odor exposures than when tested in the absence of predator odors. 

The role of chemoreception in antipredator defenses can be demonstrated by comparing the response of intact and chemosensory impaired subjects to predator scents. Laboratory studies indicate that subjects with chemosensory impairments are less responsive to predators than are intact subjects. Naive intact rats presented with cat scent exhibited freezing and micturition more frequently than did rats whose olfactory bulbs had been removed (Sieck et al. 1974). Mollenauer et al. (1974) placed intact and bulbectomized rats in a cage adjacent to a cat separated by a wire mesh. Olfactory-impaired rats exhibited fewer signs of fear, defecating less and exploring more than did intact rats. A similar approach could be implemented in the field, and survivorship of intact subjects could be compared to that with individuals whose chemical senses have been impaired (Weldon 1990). 

Response to food can be used as an indirect measure of prey response to predator scents. Stimuli can be placed either directly on the food or in close proximity to the food. For example, choice-tests were used to assess the avoidance of lion fecal odors by rabbits (Boag Mlotkiewicz 1994) and deer (Abbot et al. 1990). In both cases, subjects were offered a choice between treated and untreated pelleted food and relative intake was taken to reflect avoidance. Likewise, arena tests have been used to demonstrate that domestic livestock will investigate but reduce their ingestion of feed in the presence of predator odors (Pfister et al. 1990). Odors also can be applied to natural forage to assess whether target species avoid the treated plants (Sullivan et al. 1988 Calder Gorman 1991). Epple et al. (1995) monitored caching behavior to assess the response of mountain beaver to food resources associated with predator odors. 

Relative capture success of clean and predator contaminated traps can be an indicator of avoidance. Stoddart (1976) assessed the effects of weasel odors on trap success in a mixed community of rodents. Two traps were placed at 10-m intervals on a 6 x 6 grid. Paired traps were placed as close as possible to each other and a pretreatment period indicated either trap was as likely as the other to capture a rodent. One trap in each pair then was randomly selected to be treated with weasel and gland secretion during the treatment period. Robinson (1990) found that trapping patterns made little difference in small mammal response to mink odors. Tests results were similar regardless of whether the traps were placed in pairs immediately adjacent to each other or in rows at 10-m intervals. Tobin et al. (1995) compared the capture rate of rats in traps known to have previously captured a mongoose to that of clean traps. 

Chemical cues emitted by one species have been shown to alter the reproduction status of another species. Similar paradigms discussed above for intraspecific interactions can be used to assess whether behavioral patterns are altered because of interspecific odors. 

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Predatory fish may also be affected by alarm pheromones (Section 7.2) of the prey, both directly and indirectly. The alarm odor may act as defense compoimd that inhibits predator attack or reduces capture rate by inducing predator avoidance in school members of the prey species. 

Arnold, E. 1988. Caudal autotomy as a defense. In Biology of the Reptilia 16, Ecology B Defense and Life History (Ed. by C. Cans R. Huey), pp 235-273. New York Alan R. Liss. Brodie, E.D., Jr., Formanowicz, D.R., Jr. Brodie, E.D., III. 1991. Predator avoidance and antipredator mechanisms distinct pathways to survival. Ethol. Ecol. Evol, 3, 73—77. 

Rodents do not like to be out in the middle of a large open space. This makes sense, because going into open spaces increases the likelihood that the rodent will be spotted by a predator. Scientists can use the natural desire rodents have to avoid open spaces as a measure of how anxious a rat or a mouse is. In the defensive withdrawal test, rats or mice are placed in a bright open space that has an enclosed dark box off to one side. The amount of time that the rodent spends inside the box compared with the amount of time the rodent spends outside is thought to be a measure of anxiety. This test has been shown to be fairly sensitive to drugs. 

For most marine invertebrates that readily consume chemically defended seaweeds, it is not known whether they are actually resistant to, or simply tolerant of, algal secondary metabolites. In the case of specialist consumers (e.g., nudibranchs, ascoglossans, some amphipods or crabs see Section IV.B), a means of resistance to specific chemicals seems likely. However, for marine invertebrates that consume a diverse array of prey that produce different chemical defenses against a broad suite of predators,85,86 perhaps tolerance or less-specific mechanisms of resistance (i.e., gut pH) become more important. The actual mechanisms by which marine consumers avoid harmful effects of consuming chemical defenses (detoxification or dietary mixing) are even less well understood (see Section II.B.2). 

Other physiological effects of defensive chemicals have not been observed or studied for plant-herbivore interactions. For example, studies of chemically defended sessile invertebrates have shown that some compounds have emetic properties against fish predators, and that fishes can learn quickly to avoid these chemicals after regurgitating ingested food.206,258 Macroalgal compounds could potentially act in similar ways, but such effects have never been documented. 

In between bites, we talk about other compounds in food. Because plants are rich in sugars, proteins, vitamins and minerals, they make obvious and tempting treats for various predators. Plants cannot run away, so instead they have evolved a set of defenses to protect themselves. Celery is seemingly benign, yet it produces toxic compounds called psoralens to discourage predators and avoid being a snack too early in its life cycle. Sometimes humans are the accidental victims of psoralen poisoning. 

On the other hand, microorganisms and herbivores rely on plants as a food source. Since both have survived, there must be mechanisms of adaptations toward the defensive chemistry of plants. Many herbivores have evolved strategies to avoid the extremely toxic plants and prefer the less toxic ones. In addition, many herbivores have potent mechanisms to detoxify xenobiotics, which allows the exploitation of at least the less toxic plants. In insects, many specialists evolved that are adapted to the defense chemicals of their host plant, in that they accumulate these compounds and exploit them for their own defense. Alkaloids obviously function as defense molecules against insect predators in the examples studied, and this is further support for the hypothesis that the same compound also serves for chemical defense in the host plant. 

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