So you can give in. Get territorial and defensive. Freak out about losing your job and start hoarding your knowledge so that they need you. Work long hours and get snappy because you're getting tired and/or burned out.
Or don't. Don't get me wrong, this particular downward spiral is easy. But boy will it kill you and your career.
So decide not to.
Instead of hoarding information, find new ways to share it.
Instead of worrying out loud, be enthusiastic.
Instead of working extra long hours, work more efficiently during your normal hours (close that RSS reader!).
Choose not to engage in battles that aren't about the product and making it better.
Choose not to engage at a personal level but only at a professional level.
Remember that sometimes you win by not being the one who has to have the last word.
And every day, find a way to get yourself and someone else to smile. It's still okay to enjoy your work.