A trophic cascade is the trickle down changes in a food chain or food web caused by addition or removal of organisms at the top of the chain or web. For example, if sharks were added to a new ecosystem, the number of fish that they feed on would decrease, and the number of primary producers like algae would increase. If a renewable resource is also used by certain organisms in an ecosystem, or one of the organisms is the resource, then a trophic cascade could help show the effects of introduction of a new top level species to an ecosystem, or the effect of increased human predation of a particular species.