One of the hardest things I ever had to do was work for one supervisor while also managing the entry hall in an administrative building. When I was hired, I was assigned to handle one supervisor's schedule. However, since that supervisor's office was directly off the building's atrium, his administrative assistant had always managed the desk in the front hallway, serving as the first point of contact not just for people coming into the building, but also for people calling the department. When I took the job, I was pleased by the arrangement because I felt like I was right in the middle of things. However, it turned out that right in the middle meant that everyone in the entire building thought I might be working for them.
Next thing I knew, I was making copies for the lady upstairs; two other administrative assistants were forwarding their phones to me for nearly three-hour lunches and other "errands," and I had access to every calendar in the place "just to make scheduling easier." And it was not to make scheduling my boss' meetings with their supervisors easier, it was to help make sure I could access calendars and set meetings without even having to bother those other assistants. At first, I thought that I was working as a team. I was actually happy to have all of this stuff to do. However, the first time I got a real project with a real deadline from my own boss, I realized how much trouble I was in. I barely had time to read the background information on it between answering phones and putting out fires that should not have been mine in the first place! I knew I was going to miss that deadline if something did not change fast.
Fortunately, my boss was really understanding when I talked to him about it and sorted everything out without creating any serious turmoil - though the other administrative assistants were not happy about cutting their lunches back down to size. If you find yourself in a similar situation, before you agree to take on any additional responsibilities, talk to your direct supervisor and make sure that he or she approves the changes and that you have a very clear, written description of what will be required of you and, ultimately, who will make the decision about expanding or contracting those responsibilities. It is not unreasonable when you are first starting out in a job to ask, flat out, who you should report to. It is a responsible thing for you to do to insure that you understand the chain of command and to also guarantee that you are able to keep the number of people telling you what to do at a manageable level.