The Effect of Herbivory on Plants

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Intense grazing by herbivores can drastically affect the amount of seaweed present. Having secondary metabolites can be used as a defence mechanism. Many different genres of algae were studied, having many different types of chemical compounds found on many different parts of the world. Most studies harvested and purified samples then exposed these samples to different herbivores. The herbivores varied in size from large fish to smaller organisms such as amphipods. Aspects such as survivorship, behaviour and chemical composition were analyzed. All the studies have shown that there was an avoidance and low survivorship when herbivores were feed these samples. There also seems to be variation in chemical composition and palatability depending on where the plant is located geographically. These studies have shown that secondary metabolites can deter herbivores.


Herbivory on plants can be intense. The need for mechanisms to defend themselves against this damage is needed for the species to persist. Generally the plant has three ways strategies it can have to lessen the affects of herbivory. It can escape in time and space, decrease attractiveness and adapt to just tolerate the herbivore attack. (Duffy & Hay 1990) Although the plant may rely on strategies such as growing in large abundances, chemical adoptions still seem to play a large influential role in deterring herbivores. Using chemical compounds is just one way this organism can make itself less attractive to the herbivore. Analysis of the stomach contents in fish indicate that there is a preference of some algae and not others, this may be due to the secondary metabolites contained in certain species of algae. (Paul & Hay 1986) In the past secondary metabolites...

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...uggested that these factors may contribute to the production and distribution of these metabolites. How the algae were chemically analyzed has flaws. Although chromatography is very useful, it gives very little information about the quantitative information and concentrations of the metabolites. Also, highly polar metabolites are not as effective at detecting, and water soluble metabolites are not detected at all. This is due to their rapid degradation. (Paul & Hay 1986)

Investigations of interactions between predator and plant were common. However, the affects of these interactions on the entire community was not heavily reviewed. Although authors did mention and suspect that these relationships may have contributing factors that affect distribution, abundance of the seaweed population as well as affect other relationships that are also involved with the seaweed.

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