Effects of seed density and proximity to refuge habitat on seed predation rates for a rare and a commonLupinusspecies.
OBJECTIVE
Biotic interactions such as seed predation can play a role in explaining patterns of abundance among plant species. The effect of seed predation will depend on how the strength of predation differs across species and environments, and on the degree to which seed loss at one life-cycle phase increases fitness at another phase. Few studies have simultaneously quantified predispersal and postdispersal predation in co-occurring rare and common congeners, despite the value of estimating both for understanding causes of rarity.


METHODS
We quantified predispersal seed predation on the rare, herbaceous speciesLupinus tidestromii(Fabaceae) and its common, shrubby congenerL. chamissonisacross multiple years in the same community. We experimentally measured postdispersal seed predation at two seed densities and locations near or far from an exotic grass housing high densities of deer mice (Peromyscus maniculatus), their primary, native seed predator.


RESULTS
The commonL. chamissonishad the lowest predispersal seed predation of the two lupine species, potentially because of its height: its high racemes received less predation than those low to the ground. By contrast, the same species experienced higher postdispersal seed predation, and at predators traveled long distances away from refuge habitat to consume their seeds. Across both plant species, mice preferentially predated high-density seed sources.


CONCLUSIONS
Our results show differences in the magnitude and direction of seed predation between the species across different life-cycle phases. We demonstrated possible roles of proximity to refuge habitat, seed density, and seed size in these patterns. Congeneric comparisons would benefit from a comprehensive framework that considers seed predation across different life-cycle phases and the environmental context of predation.
Environmental Studies, Washington University in St. Louis, 1 Brookings Drive, Box 1137, St. Louis, Missouri 63130, USA epardini@wustl.edu.
Eleanor A
EA
Pardini
Romberg Tiburon Center for Environmental Studies, San Francisco State University, 3150 Paradise Drive, Tiburon, California 94920, USA.
Melissa V
MV
Patten
Institute of Biology, Martin Luther University Halle-Wittenberg, Am Kirchtor 1 06108, Halle (Saale), Germany.|Department of Community Ecology, Helmholtz Centre for Environmental Research-UFZ, Theodor-Lieser-Straße 4 06120, Halle (Saale), Germany.|German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e 04103, Leipzig, Germany.
Tiffany M
TM
Knight
D000818:Animals; D002140:California; D017753:Ecosystem; D031297:Lupinus / Q000502:physiology*; D010542:Peromyscus / Q000502:physiology*; D011157:Population Dynamics; D058614:Seed Dispersal; D012639:Seeds / Q000502:physiology; D061350:Sympatry
Lupinus; Point Reyes National Seashore; apparent competition; congeneric comparisons; plant height; rodent seed predation; seed density; seed size