Predation compounds

The effects of pollution can be direct, such as toxic emissions providing a fatal dose of toxicant to fish, animal life, and even human beings. The effects also can be indirect. Toxic materials which are nonbiodegradable, such as waste from the manufacture of insecticides and pesticides, if released to the environment, are absorbed by bacteria and enter the food chain. These compounds can remain in the environment for long periods of time, slowly being concentrated at each stage in the food chain until ultimately they prove fatal, generally to predators at the top of the food chain such as fish or birds. 

Although no consistently effective chemical repellent has been developed for vertebrate pests, some promising materials have been tested as repellents that are based on predator avoidance, specifically compounds from the secretions of predators. In 1995, synthetic sulfur compounds (two thietanes, a thiolane, and a substituted methyl sulfide, which were originally identified from the anal glands of the stoat, ferret, and red fox) suppressed browsing by the introduced AustraUan bmsh-tail opossum in New Zealand about as well as FEP (83). Suggestions were made that these compounds can be made more effective by the use of bitter compounds in a cocktail. 

The addition of oxides to ceramic bodies and to glasses to produce color has been known since antiquity (2). The use of iron and copper oxides predates recorded history. Cobalt was introduced into Chinese porcelain about 700 AD. Chromium compounds have been used since 1800 AD. 

Aquatic organisms, such as fish and invertebrates, can excrete compounds via passive diffusion across membranes into the surrounding medium and so have a much reduced need for specialised pathways for steroid excretion. It may be that this lack of selective pressure, together with prey-predator co-evolution, has resulted in restricted biotransformation ability within these animals and their associated predators. The resultant limitations in metabolic and excretory competence makes it more likely that they will bioacciimiilate EDs, and hence they may be at greater risk of adverse effects following exposure to such chemicals. 

The cyclooligomerization of ethylene oxide to yield dioxane as well as compounds we now call crowns predates Pedersen s discovery by more than a decade ". The full utility of these cyclic oligomers was not recognized, however, and the patent reporting these early efforts remains an interesting historical footnote. The promise of utilizing cyclo-oligomerization commercially is so important, however, that attention is called to the method and the existence of the patent. 

An excellent review by Roth and Eisner (63) summarized the chemical defense substances found in arthropods up to 1962. These authors listed 31 defense substances of known structure one anhydride, three carboxylic acids, nine aldehydes, one furan, three hydrocarbons, two ketones, one lactone, eight quinones, and three inorganic compounds. Many of these same compounds (unsaturated aldehydes and quinones) have been found in other arthropods since 1962 (38). The compounds are discharged when the animal is disturbed by predators, and there can be no doubt that the action of most of them... 

Neurotoxic compounds can have behavioral effects in the field (see Chapters 5, 9, and 15), and these may reduce the breeding or feeding snccess of animals and their ability to avoid predation. A number of the examples that follow are of sub-lethal effects of pollutants. The occurrence of sublethal effects in natural populations is intimately connected with the question of persistence. Chemicals with long biological half-lives present a particular risk. The maintenance of substantial levels in individuals, and along food chains, over long periods of time maximizes the risk of sublethal effects. Risks are less with less persistent compounds, which are rapidly... 

When used in this controlled way, there is still concern that these compounds may be transferred via rodents to terrestrial predators and scavengers that feed... 

In contrast to the controlled use of these compounds in the neighborhood of farms and human habitation, they have sometimes been used in a less controlled way against rodents and vertebrate predators, which causes problems in conserved areas. In a number of conserved islands in New Zealand, for example, bait containing brodiphacoum has been used for rodent control, both at bait stations and by aerial distribution (Eason et al. 2002). In the latter case, poisoned bait is freely available, and herbivores and omnivores, as well as predators and scavengers are at high risk. This problem will be discussed further in Section 11.6. 

In summary, there is as yet no clear evidence that superwarfarins have caused any widespread declines of predators and scavengers that feed on rodents. However, the persistence and very high cumulative toxicity of these compounds suggest that they could pose a serious hazard to such species if they were to be more widely used. The situation needs to be kept under close review. 

The chloride anion is a major species in the oceans and plays an essential role in biochemistry. Compounds containing carbon-chlorine bonds occur much less frequently in nature. Volcanos emit some halocarbons, and marine algae generate chloromethane. Other marine species produce toxic organohalogen molecules that protect them from predators. Nevertheless, organic chlorine compounds are uncommon, and consequently there are few mechanisms that degrade them. 

At the other extreme, if metabolism of the xenobiotic by the organism does not occur at all—or at insignificant rates—after exposure, the compound will be persistent in the organism, and may therefore be consumed by predators. This is relevant to biomagnification. 

The relative toxicity, especially of the newer compounds, to various pests and species is of practical importance, as are also differences in species tolerance to DDT and other sprays. This is also of direct concern in relation to parasites and predators. There is interest in synergistic action and the effect of spreaders, stickers, and related products. The effect and use of repellents and attractants have received attention. 

Skunks deter predators by release of a liquid spray containing seven major volatile components classified as thiols (compounds containing the -SH functional group) and acetate derivatives of thiols (characterized by the SC(0)CH3 functionality). In particular, two of the more odiferous components responsible for the strongly repellent odor of the skunk s secretion are 2-butene-1-thiol (Fig. 13.2.1) and 3-... 

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