Influence of patch characteristics on pollinator behavior and seed production in Centaurea stoebe

Discontinuous, or patchy, landscapes may affect pollinator foraging behaviors and could potentially lower the fitness of isolated plant communities by limiting and/or altering pollination services. I tested this idea by examining changes in pollinator behavior in patches of spotted knapweed of different size, flower density, and distance from one another. Based on predictions from optimal foraging theory, I identified and measured key pollination promoting behaviors that may change when foragers are exposed to discontinuous landscape. These behaviors were pollinator visitation rates to patches, the number of visits to individual flowers within patches, and the handling time per flower. These factors were then correlated with changes in patch characteristics and plant seed set. For this study, 30 patches of spotted knapweed, Centaurea stoebe L. ssp. micranthos, were identified and surveyed across the Syracuse, New York area. These 30 patches differed in three main patch characteristics: flower density (number of flowers per m2), patch size (m2), and average patch distance from neighboring patches (m). Within each patch, observations of the key pollination promoting behaviors were documented. Statistical analyses relating these variables to seed production demonstrated that the number of visitations a flower received was the behavior most associated to seed production, with a strong positive correlation. In addition, flower visitation was influenced most by patch size and average patch distance, with patch distance also having a strong negative correlation to seed production. The results suggest that average patch distance indirectly affects seed set by influencing pollinators’ frequency of visitations per flower. Therefore, plants in patches that are more geographically isolated from other patches may experience lower fitness.