Note: If your PI already has a grant on this topic, you are not likely to be funded; If “existing funds” are available for the proposed work, you are disqualified. The important point being that these proposals are used to gauge the independence of the PhD candidate from the PI’s major research thrust.
Why else consider writing a DDIG? The fame …The glory…The practice and most importantly…Excellent odds (25-30% funding rate)
1. The NSF DDIG Page
2. Links to the two sections of NSF through which DDIG's are funded: DEB and the Behavior cluster at IOS.
3. Student resources at the Indiana University Biology Department for DDIG submissions
*warning, some of the links on that page are out of date but the advice documents are still useful
4. Successful DDIG's from Stonybrook
5. One and Two posts from Joan Strassman's blog.