General Information on NIH Funding Mechanisms
First, visit http://grants.nih.gov/grants/funding/funding_program.htm
NIH is broken up into institutions. Check out the different institutes at http://www.nih.gov/icd/
Particular institutes of interest for population biologists include:
Study Sections review grants.
You can search for opportunities at: http://grants.nih.gov/Grants/guide/search_results.htm?year=active&scope=pa
Types of Awards for Faculty and Institutions
Resources Specific to Graduate Students
The main NIH funding mechanism for individual grants to graduate and postdoc students are Ruth L. Kirschstein National Research Service Awards (NRSA). The NRSAs come in two flavors, F31 and F32. F31 are for graduate students. F32 are for postdoctoral students. More information to get you started can be found at: http://grants.nih.gov/training/nrsa.htm.