I am curious to know if the shaman's spirit companion is consider the same as the shaman for effects that pertain to him. In particular, if I have a power that says something like "at the start of each of your turns, any enemy adjacent to you are blank...", will the power's effect trigger if they are next to my spirit companion instead of my player character if the power doesn't explicitly mention the companion?
Unless Specified by another source, Powers, Feats, and Features only affect what they say they affect.
Your powers won't automatically work for your spirit companion unless they say they do.
There is a rather exhaustive treatise on Spirit Companions here.