Cost-effectiveness, chemical defensive

Chemical vapor sensors play an ever-increasing role in the environmental monitoring, homeland security, defense, and health care. The desirable characteristics of a chemical vapor sensor include ultrahigh sensitivity, specific and rapid response to certain vapor molecules, as well as the ability for on-the-spot chemical analysis, which usually requires the sensor to be small, portable, reusable, stable, robust, and cost effective. Toward this end, various sensing techniques have been studied... 

Evolution of chemical defenses according to the optimal defense theory presumes, in addition to costly defenses, that there is genetic variation for the defensive metabolites, that herbivory is the major selective agent for such metabolites, and that the chemical trait in question is efficient in reducing herbivory (Stamp 2003). Research on macroalgal chemical defenses has strongly emphasized the last precondition, which has mainly been studied by testing the deterrence effects of secondary metabolites in bioassays. The defensive role for the trait has been assumed on the basis of deterrence it provides. Veiy little research on the first two... 

Many intertidal and shallow subtidal habitats are highly variable over space or time. Consequently, the concentrations of chemical defenses that are appropriate at one place or time may be inappropriate at another. A strategy for dealing with this variability is the detection of an environmental cue that can be correlated with an appropriate level of defense for that environment at that time. One of the best examples of environmental cues causing changes in chemical defense concentrations are herbivore-induced defenses in which chemical levels are increased in response to an attack by a consumer.136 137 Induced defenses require that herbivory be variable and unpredictable, that the inducing cues produce effective increases in defenses, and that the induction is cost-effective and rapid enough to deter further consumption.140... 

Indirect defense Chemical compounds attract natural enemies of an herbivore to locate a suitable prey after attack (also termed top-down effects or multitrophic Interactions) Indirect defense Is normally inducible and thus cost effective under a low herbivore environment. Effective only if natural enemies are within the range of spreading signals... 

Anti-predator adaptations are often mediated or induced by chemical cues (Kats and Dill, 1998), especially in aquatic systems where visual cues are limited (Smith, 1992). Chemical cues function well in this medium as a large number of compounds can dissolve in water allowing for the production of a great number of possible signals (Hara, 1994). Research, in the past decade, has indicated that the assessment of these chemical cues is highly sophisticated (reviews Chivers and Mirza, 2001). Logically, the ability to accurately assess the risk of predation would be beneficial as each anti-predator defense has an innate cost to the user and the effectiveness of each response option is dependent on the context of the encounter and the specific predator. 

---