Predators, are they important?

I saw a preview for an episode that PBS was going to be putting on in the next few days. The show was about the importance of the predator in nature. It will be talking about what effects predators have on ecosystems and what happens when there is a lack of predators. The predators mentioned range from sharks and how they effect ocean life to wolves in Yellowstone and what effects they have. Since the show has not been on yet I am not sure about everything it will talk about but I did look it up on the PBS website and you can go here to find a lot of good information. The program schedule said that the episode will be on KUED Channel-7 Wednesday April 27th at 8:00p.m. I would encourage you to watch, I also recommend the show on any other day.