Lecture 16: Food Webs & Trophic Levels Revisited

There are three essential types of food webs:

The food web below is a CONNECTEDNESS web, showing the relationships between what organisms consume other organisms. It is important to know that, due to omnivory, our basic conceptions about rigid trophic levels do not hold up, as a single organism (such as humans) can move arbitrarily among multiple trophic levels.
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The next food web is an ENERGY FLOW web, which appears to have similar connections to the connectedness web, but instead of simply showing consumption patterns, this type of web takes into consideration the trophic levels' and organisms' relative use of energy and, thus, the overall transferred energy flows that occur as a result of various degrees of predation in the food web. It can show, for instance, how an animal eating a lower trophic level organism with regularity can get significantly more energy (revealed by a thicker arrow) than it would when it occasionally eats a higher trophic level predator.

The final food web is a FUNCTIONAL web, which boils down the complicated interactions within the community's food web into showing those interactions with the most influence on determining population levels and possible growth or decline of other organisms in the community. The idea of the functional food web connects into the idea of trophic cascades based on dominant predators.

Also, I found the first half of this youtube video to be helpful in understanding bottom-up and top-down trophic cascades
http://www.youtube.com/watch?v=yg5ieYKvYI8

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