Why is it important for scientists who study ecosystems to study more than the organisms that live there?

Because other things effect them, like our polution, even in places where we don't live we still have an effect, our furtilizers polute water, paper mills and cars polute the air. Also some animals just pass through but aren't perminant residence but still effect what's going on, the like is a complicated web of interrelatedness, ever hear of the butterfly effect, no, not the movie, but is is something like a butterfly flapping it's wings on one side of the world will cause a tornado on the other (note note the actual saying but close enough) what I am trying to say is that even though an organism doesn't live there doesn't mean that it doesn't effect the life that is there.

Hold on to his or her beliefs even if there is no evidence for those beliefs.