Monday, August 3, 2009

PS 19-161: Lupine seed predation: The effects of seed color and substrate

Ellen F. Wakeley and Helen J. Michaels. Bowling Green State University


Lupinus perennis (Wild blue lupine) is an integral part of midwestern oak savannah ecosystems. Because lupine provides food and habitat for the animals of the oak savannah, including several endangered or threatened butterflies, it is necessary to understand what happens to seeds after they disperse to determine the long-term viability of populations. Lupine populations are often managed by fire, which alters litter and vegetation density as well as soil characteristics. We hypothesized that the rate of seed removal by animals would be affected by seed coat color and substrate color; specifically, that those seeds that are similar in color to the substrate will be taken less often because they are more difficult for predators to see. A four-week pilot study documented variable seed removal, after which a five-week seed color/substrate experiment tested for differences in seed removal rates using light vs dark colored seeds and substrates created using field collected surface material from burned and unburned patches. Spatial patterns in seed removal rates were also assessed using GPS points and ArcGIS.


In the seed color/substrate experiment, both seed color and week were significant in determining seed removal rates. Removal rates increased as the weeks progressed.  Seed removal rates averaged 62% across all treatments. Analyses showed that dark-colored seeds had higher predation rates than light-colored seeds, regardless of substrate. Dark seeds on the sand background had the highest removal rates, while white seeds on the sand background had the lowest, consistent with trends predicted from our hypothesis. This study suggests that seed predation rates may significantly impact recruitment, and that these effects may vary depending on population-specific seed coat patterns and management history of the site.  Results from the spatial data are in progress.