Sponsors of traumatic brain injury project.

www.sciencemag.org SCIENCE VOL 329 16 JULY 2010 249 COVER A seedling carpet dominated by Dipteryx oleifera (almendro) in the forest understory of Barro Colorado Island, Panama. Seedlings here have a lower probability of surviving when surrounded by neighbors of their own species. However, rare species suffer more from the presence of like neighbors than do common species, suggesting a mechanism that shapes species abundances in diverse tropical forest communities. See page 330. Photo: Christian Ziegler DEPARTMENTS 254 This Week in Science 258 Editors’ Choice 260 Science Staff 261 Random Samples 346 New Products 347 Science Careers page 270 EDITORIAL 257 A Volunteer Army for Science Donald G. Rea and Katherine M. Nielsen