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 for its consequences (a “trophic cascade”) as persuasively as the re-introduction of wolves into Yellowstone.  Hmmm….  Am I overstating?  I suppose it could easily be argued that we’re changing variables within the natural world all the time and that we are confronted only too dramatically, far too often, with appalling consequences! But this example, unlike many, involves action deliberately chosen with prediction of good consequences for the natural world.  And, unlike many, it is beautiful and hopeful to take into class.