A top-down cascade is a trophic cascade where the top consumer/predator controls the primary consumer population. In turn, the primary producer population thrives. The removal of the top predator can alter the food web dynamics. In this case, the primary consumers would overpopulate and exploit the primary producers. Eventually there would not be enough primary producers to sustain the consumer population. Top-down food web stability depends on competition and predation in the higher trophic levels.
I thought learning about the top-down cascade is intriguing to learn about, especially seeing how invasive species and humans have an effect on the trophic cascades (webs). Would invasive be considered, in some sense, to be keystone species because they can alter cascades by removing or becoming a top predator?