Our focus this week is on ecology. Ecology is the study of interactions among organisms and between organisms and their physical environments. Watch the video Some Animals Are More Equal Than Others: Keystone Species and Trophic Cascades [Video], then address the following two issues:

Why do you think that many keystone species are predators at the top of the food chain in their respective ecosystems?
What do you think is the most interesting or significant facet of the video?