Effects of local conspecific density on reproductive success in Penstemon digitalis and Hesperis matronalis

We investigated the effects of plant density on reproductive success for tw o insect-pollinated plant species-the native North American wildflower Pens temon digitalis (Foxglove-leaved Penstemon), and the showy introduced weed Hesperis matronalis (Dame's Rocket). We found no indication that local dens ity (within 3.0 m) affected reproductive success (seeds per fruit, proporti on fruit set, total seeds per plant) for either species. Penstemon digitali s suffered heavy fruit predation from micro-lepidopterans, and such damage tended non-significantly to increase with density. We discuss the reasons f or our results, and suggest that an understanding of those causes is import ant for conservation.