6) If the Brown Rat was taken out of the ecosystem, all the other biotic and abiotic factors would be affected. Since the Brown Rat eats everything except the barn owl, the deer mouse, meadow vole, eastern mole and northern pocket gopher populations would increase rapidly. With the increase in these populations, the number of seeds and the amount of fruit would decrease making less food for these growing populations. With no new seeds, no more trees and vegetation would grow making less food and shade in the ecosystem. With no shade the grass would soon dry out and die. Then when they start to all die out because of no food, there would be no food for the barn owl and they would die out. The whole ecosystem would be affected.

In the Discovery Bay part of Planet Earth, I would say there are three major populations integral to the story of this ecosystem. The three populations, in order, are humans, large predator fish, and small herbivore fish. The main problem is that the habitat of these fish are being destroyed because of destructive, unsustainable fishing methods. Their habitat, the coral reef, is being hurt due to the taking away of large predator fish. Predation is the main thing among these three populations, the humans take the large predator fish as their prey and the large predator take the small herbivore fish as their prey and the small herbivore fish feed on the algae to protect the coral reef. The relationship between the small fish and the coral reef might be better known as mutualism, small fish feed on algae while the reef offers them protection. 

The ripple effect is that since the humans fish out all the large fish the next closet thing is the small fish since the large fish have fled the scene. Since the small fish are gone there is nothing left to eat that algae that would otherwise suffocate the reef. With the reef suffocated there is no more habitat and no more thriving ecosystem. What has helped relieve this decline is the making of protective zones which has started to bring back some of the larger predators.