Just a little aside, when I approach a jam circle, I'll stand to the side and either watch or play quietly. I will only join in if so invited. Sometimes if the partcipants in the jam are way above my level, I graciously decline. When I'm in a jam, I try not to play too loudly, over the singer or soloist or not play at all if I don't know the chords to a particular song.
While I'm not a hot player by any means, I can play a simple melody or improvise enough so it sounds OK. What I find happens at the closing jam circle, is that some players, once they hear you're not up to their speed, will try to edge you out. I have other players complain about the same thing, especially about one group of jammers.
Las Vegas, NV
"Every day brings a chance for you to draw in a breath, kick off your shoes and play your mandolin."