Predation sensitivity

Second, the increased movement necessary for locating widely dispersed feeding sites should increase contact rates with enemies. Movement makes insects more conspicuous to parasitoids or predators sensitive to it (50,51). Random encounters with arthropod predators or parasites should increase with searching activity, as would risk of dislodgement and fallout. 

In addition to reproductive effects, fish exposed to endocrine disrupters may have a decreased response to stress or decreased growth and metabolism which can affect their ability to survive, or to defend themselves against predators. All of these factors can affect the ability of the species to survive and to reproduce itself in sufficient numbers to maintain the stocks on which our commercial and sport fisheries are based. Not all fish species will be equally susceptible to the effects of endocrine disrupters. Selective sensitivity to such effects, especially those affecting reproduction, may well lead to major changes in the flora and fauna of some of our major aquatic ecosystems as the balance between fish, mammals, invertebrates and plants, and between predators and prey, is destabilised... 

Sensitive sites would include sites that are receiving high inputs of atmospheric Hg deposition and sites with aquatic ecosystems where top end predators have high levels of Hg. We also recommend that urban sites with elevated atmospheric Hg deposition and forest sites with shallow hydrologic flowpaths, wetlands, and unproductive aquatic ecosystems should strongly be considered as candidate sites. 

Invertebrate species have been widely used in toxicity studies of pesticides [61]. Zooplankton play a key role in the food chain because they occupy a central position. Therefore, their responses to natural and anthropogenic stresses are intimately linked with other food predator organisms. The most widely accepted bioassays employ species such as Ceriodaphnia dubia, Daphnia magna, Artemia salina, or Thamnocephalus platyurus [62-64]. D. magna has been used for many years as a standard aquatic test species and formally endorsed by the major international organizations such as the EEC, OECD, and ASTM [65-67]. Its choice is mainly because it represents the zooplankton community and is a species of worldwide occurrence. In addition, it has a greater sensitivity to toxicants, particularly pesticides, compared with other aquatic species [61,68] (Table 1). 

The ability of olfactory systems to cope with this plenitude of stimuli together with the fact that specific volatile compounds became associated with different plants and animals and different body sites, glands, and metabolites, provided exquisitely sensitive and accurate cues to the identities of places, trails, individuals, prey, predators, mates, social groups, and food. Olfaction permitted the development of a heretofore unparalleled perceptual talent. 

Like pit vipers and wall lizards, various mammals are also sensitive to a predator s scent. Oftentimes, their best defense is retreat, and so frightened deer and squirrels withdraw quickly when they... 

Several predation tests especially with spiders and blister beetles [121,313, 314], show that spiders exhibit a wide range of sensitivities to meloid beetles as prey. In the racoon Procyon lotor it was shown that they quickly form an aversion to blister beetle prey, which is induced by cantharidin [314]. 

This does not mean that the thyroid hormones are normally detrimental to survival in starvation. Laboratory animals are protected from factors such as marked fluctuations in ambient temperature, the need to find food, and from predators such problems in the wild require the action of triiodothyronine, to increase the sensitivity of regulatory mechanisms to aid the response to such problems. High rates of energy expenditure are therefore, essential for survival in the wild ... 

Acidification of acid-sensitive waters is accompanied by severe changes in biological communities. Effects range from reductions in diversity without changes in total biomass to elimination of all organisms. In many cases the immediate cause of the changes is unknown. Some effects are the result of H" toxicity itself or of the toxicity of metals mobilized from the watershed, others have more indirect causes such as changes in predator-prey interactions or in physical conditions of lakes (ex. transparency). [14]... 

The most celebrated mammalian olfactory detector is the dog s nose. As a predator, the dog locates its prey by air scenting (following a gradient of airborne odors) and tracking. Practitioners are familiar with the extreme olfactory sensitivity of the dog. The detection threshold for butyric acid has been determined as 9 x 10 molecules/cm air (Neuhaus, 1953). Considering that... 

Deer mice, P. maniculatus, on an island (Moresby Island, Gulf Islands, British Columbia) that now lacks their usual predator, the short-tailed weasel, M. erminea, still respond to its odor. However, they only show the more delayed and prolonged stress-type, opioid-sensitive behavior. By contrast, this island population has lost its fear and flight responses, which are benzodiazepine sensitive and more immediate. Mainland deer mice that are sympatric with weasels show both types of response (Kavaliers, 1990). 

The purpose of the venom is offensive while that of a poison is defensive, which in turn influences the characteristics of the toxin. Venoms, either large or small molecules, are usually variants of essential biological molecules such as lipids, steroids, histamines or other proteins. They are often mixtures with a specific mechanism of action such as paralyzing the nervous system. Poisons are designed to teach a predator that this is not a good meal. They usually cause more localized pain to discourage a predator, but depending on the dose and sensitivity of the individual, the poison can be deadly. 

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. 

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