How wolves change rivers: variables and causation

This four and a half minute video, with splendid filming of animals in Yellowstone National Park in the USA, could be effective in a TOK class on the topic of the search for cause in the natural and human sciences: http://youtu.be/ysa5OBhXz-Q  It could be used to stir thoughts (or summarize them) about causes, variables, experimental controls, and the limits of experiments outside a lab. It's not often that in nature, with all its intricately interconnected variables, one variable can be be traced ...