Life feeds on life. This is necessary. ~ Tool
Not necesarily. Plants cover our entire globe, and feeds on water and sunshine. Life needs fuel, and since you can trust successful life to harbor lots of fuel - then your fellow life forms are an obvious source of allready gathered fuel.
The workings of the first life on earth makes this very interesting to consider. What are the first predators?
Well, the very first mobile organisms found that mobility allowed them to absorb silt and stuff at more efficiency. The first predators were those organisms who found it convenient to simply move themselves on top of another organism, and stay there, absorbing it slowly - since that organism had allready gathered a lot of energy beforehand.
Our herbivores are in many ways predators of non-mobile organisms, while what we normally consider predators are those who eat fellow mobile organisms. Plants eat nobody, but definitely benefit on the same prospect, as plants do considerably better growing in soil consisting of rotten organic vessels, full of stored up energy - but it is still not a definite prerequisite, as many life forms can survive entirely on absorbing "non-living" energy.
