Ethics of the Goal of life

Aristotle's approach to ethics was, "If life is worth living... it must surely be for the sake of something that is an end in itself" (Encyclopedia Britannica, Aristotle: happiness, 22).

Aristotle talks of ethics and virtue in human, that we all must have a function and it has to be more than nourishment and growth, because plants and animals do the same, so reason must come into play.  "The highest human good is the same as good human functioning"(same as above). 

Is this saying that only humans can be virtuous.  Considering all organisms, how does ethics play a roll in the goal of life, for all creatures? Can Micro organisms reason? Can animal and insects reason? Why must one connect all organisms when ethics is being discussed.