http://www.nytimes.com/2007/03/30/science/30sharks.html?_r=1&ref=science&oref=login

The food chain is a perfect example of a natural graph. This dependency network graphs different species as nodes, and links them to other species/nodes that they consume. However, what would happen if you increased the “flow” along one of these edges? How would this effect the rest of the chain? In a recent study, researchers are concluding that the decrease in shark population has caused scallop beds in North Carolina to be practically wiped out. The absence of these large predators is mostly due to overfishing and an increased demand for meats and fins, something that humans can be entirely attributed to. This has all caused sharp declines in the shark population, which in turn has caused an increase in all the creatures that sharks consume. These creatures mainly consist of smaller sharks, skates and rays. The increase in these animals has in turn caused a decrease in their prey. In this article, the decrease in sharks led to an increase in cownose rays, which has led to the nearly wiped out scallop beds in North Carolina. This entire process demonstrates the idea of trophic cascades. This occurs when the predators in a food chain suppress the majority of their prey, and thus, free the next lower level in the chain from predation. The abundance of cownose rays during their southward migration along the Eastern seaboard resulted in the depleted scallop beds.
By drastically decreasing one node in this graph, you get an accordion effect on the rest of the graph. The level just below it will increase and the level just below that one will decrease, and so on and so forth. Researchers are trying to determine how long this effect stretches down the food chain, and how meaningful it actually is. It is interesting to see how the decrease of an extremely large predator, which is high up on the food chain, can cause so many problems for the rest of the ecosystem. This trophic cascade could stretch even further than the scallop beds, if other animals depend on those scallops for survival. The entire food web is affected because of the drastic impact that the decrease of large sharks have on the ecosystem.