Herbivores Subject

If herbivore attack can lead to reduced food quality of plants, then it seems reasonable that naturally attacked plants should exhibit decreased food quality compared to naturally unattacked ones. On the other hand, there is considerable evidence that herbivores preferentially attack plants or tissues of high food quality Q). In other words, plant food quality can probably act both as a dependent and an independent variable as far as degree of herblvory is concerned. Therefore, conclusions drawn from comparisons of foliage properties of naturally attacked versus naturally unattacked plants are likely to be confounded by the interaction of these two effects. To avoid this problem the following experiments were conducted by subjecting plants to attack by Insects placed on them by the Investigators. 

It is believed that the presence of secondary metabolites impacts on the survivorship of a cyanobacterial strain in reef habitats that are subject to intense herbivory. Under suitable environmental conditions, cyanobacteria undergo rapid increases in population size, generating large cyanobacterial mats which are not calcified or of tough texture and which therefore present a potential source of food for herbivorous fish and other generalist predators. By restricting predation, potent cyanobacterial toxins facilitate the formation of cyanobacterial blooms.48... 

The spatial-variation-in-consumers model (SVICM) was proposed by marine ecologists to explain both interspecific and intraspecific patterns of chemical defenses in seaweeds.111 It states that chemically defended seaweeds will be more evolutionarily persistent than undefended seaweeds in areas subject to significant herbivore impact. Likewise, this model explains intraspecifc variation in chemical defenses, in that well-defended individuals or populations will be more persistent over ecological time scales than undefended seaweeds in areas subject to significant herbivore impact. This model borrows heavily from the optimal defense theory, in that it suggests that seaweeds that occur in areas with high herbivory pressure will be vulnerable to herbivore attack and should thus be heavily defended. 

This high elevation plant diversity harbors extended animal communities which have not been sufficiently well studied. However, in as much as cross pollination and non-wind seed dispersal are fundamental mechanisms for plant species survival, this fauna is of crucial importance to vascular plant life. Although animal life is beyond the scope of the present chapter, the interested reader might find some specific reports instruetive (e.g. Pefaur and Duellman, 1980 Pefaur and Diaz de Pascual, 1985 Vuilleumier, 1986 Hoffstetter, 1986 Cei, 1986 Reig, 1986 Holloway, 1986 Villwock, 1986 Durant et al., 1994 Diaz et al., 1997). As far as arthropods and their influence in secondary plant metabolism, their species diversity has been observed to decline with elevation in some places (e.g. Fleishman et al., 1998). Some exceptions exist as the case of mite s abundance and species diversity in the Appalachians illustrates (Lamoncha and Crossley, 1998). However, more important than species richness to herbivory pressure is the number of individuals forming a herbivore population, a subject that requires further attention in high elevations before a clear picture on their influence on secondary plant metabolism may be assessed properly. 

In this review, we examine the induced chemical defenses of P. abies, defenses whose levels increase following herbivore or pathogen attack. Induced defenses have attracted much attention in recent years because of their widespread occurrence in plants and their usefulness as subjects for study. Here, we cover the induction of several different classes of induced defenses in P. abies, including terpene-containing resins, phenolic compounds, and chitinases. Our focus is not only on their defensive roles, but also on how the levels of these compounds may be manipulated by biochemical and molecular methods while minimizing other phenotypic changes. Manipulation of defense compoimds in intact plants is a valuable approach to assessing their value to the plant. 

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